application

model grammar version 89

model	105	application
interface	20	interface
auto-webclient	xindi.1	generator_settings
		generator_annotations
		phrases
		query
		translations
		parameters
connector	36.5	processor
		variables
datastore	113	consumed_interfaces_mapping
		provided_interface_implementation
		migration_mapping
		regular_expression_engine
relational-database-bridge	109	database
		database_transformation
sql-mirror	109.1	sql_mapping
webclient	xindi.1.1	views
		widget
		client bindings
		gui_model
		phrases
		translations
		settings
		parameters
project-build-environment	41	wiring
		deployment

The minimal model
Data model structure
1. The root rule
2. Node types
References
Derived values
1. Upstream, downstream, and sibling dependence
2. Expressions
Permissions and Todos
Commands and Timers
Metadata
Navigation
User interface annotations
1. Overview
2. Actions
3. Commands
4. Groups
5. Collections
6. Numbers
7. Files
8. Texts
9. State groups
10. States
11. Todo items
12. Numerical types

The minimal model

Every valid Alan model instantiates the root rule. From that rule we can extract a minimal model. In the application language, the minimal model is

users
	anonymous
interfaces
root { }
numerical-types

Thus, every application model defines users for access control, interfaces specifying operations and data from external systems, a root type, and numerical-types. The next section explains the minimal model in more detail.

Data model structure

The `root` rule

Application users

The language supports two classes of users: anonymous users and dynamic users. Anonymous users do not require login; dynamic users do.

The keyword anonymous enables anonymous user access to your application. If you do not plan to support anonymous users, you just leave it out: the 'no' state for 'allow anonymous user' is the default, requiring no code at all.

If your application supports a dynamic collection of users, you can enable user sign-up and authentication. Enabling user sign-up means that your application will have a sign-up page for new users.

User authentication can either be application-specific, or it can be done via a single application for single sign-on. For an application that handles user authentication, you need to specify:

a collection that holds Passwords and some required properties, or
an Authorities collection listing third parties that handle authorization using the OAuth standard (Google, Microsoft, etc.). For application-specific user authentication, you need to specify which collection and text property holds (hashed) user passwords. In addition, you have to specify states for the ‘active’ and ‘reset’ status of the password.

The following model expresses an application that supports all aforementioned features:

user sign-up, by providing a user-initializer
password authentication, by specifying a Passwords collection and required properties
third party authentication, by specifying an Authorities and Identities collection

users
	dynamic: .'Users'
		user-initializer: (
			'Type' = create 'Unknown' ( )
		)

		passwords: .'Passwords'
			password-value: .'Data'.'Password'
			password-status: .'Data'.'Active'
				active: 'Yes' ( )
				reset: 'No' ( )
			password-initializer: (
				'Data' = ( )
			)

		authorities: .'Authorities'
			identities: .'Identities'>'User'
			identity-initializer: ( )

root {
	can-update: user .'Type'?'Admin'

	'Users': collection ['Name'] {
		'Name': text
		'Type': stategroup (
			'Admin' { }
			'Unknown' { }
		)
	}
	'Passwords': collection ['User'] {
		'User': text -> ^ .'Users'[]
		'Data': group {
			can-update: user is ( ^ >'User' )

			'Password': text
			'Active': stategroup (
				'No' { }
				'Yes' { }
			)
		}
	}
	'Authorities': collection ['Authority'] {
		'Authority': text
		'Identities': collection ['Identity'] {
			'Identity': text
			'User': text -> ^ ^ .'Users'[]
		}
	}
}

The initializers are for setting initial values for a user, password or identity node. For example, the user-initializer sets the Type of users that sign up to Unknown. Thus, users cannot sign up as an Admin; Admin permissions are required to make a new user Admin.

'allow anonymous user': [ users ] stategroup (
	'no' { }
	'yes' { [ anonymous ] }
)

'has dynamic users': stategroup (
	'no' { }
	'yes' {
		'users collection path': [ dynamic: ] component 'descendant property path'
		'supports user sign-up': stategroup (
			'yes' {
				'user initializer': [ user-initializer: ] component 'user initializer'
			}
			'no' { }
		)
		'has password authentication': stategroup (
			'yes' {
				'passwords collection path': [ passwords: ] component 'descendant property path'
				'password text path': [ password-value: ] component 'descendant property path'
				'password status': [ password-status: ] group {
					'state group path': component 'descendant property path'
					'active state': [ active: ] group {
						'state': reference
						'initializer': component 'command object expression'
					}
					'reset state': [ reset: ] group {
						'state': reference
						'initializer': component 'command object expression'
					}
				}
				'password initializer': [ password-initializer: ] component 'password initializer'
			}
			'no' { }
		)
		'has external authentication': stategroup (
			'yes' {
				'authorities path': [ authorities: ] component 'descendant property path'
				'identities path': [ identities: ] component 'descendant property path'
				'user reference': [ > ] reference
				'identity initializer': [ identity-initializer: ] component 'identity initializer'
			}
			'no' { }
		)
	}
)

Interfaces

If your application consumes data from external sources, you will have defined an Alan interface. In order to consume an interface, you have to mention it in the interfaces section. This way, you can reference the interface when configuring permissions. The path is for specifying on which node the interface conformant data will be imported at runtime.

The node itself may only be modified via the interface: the value source has to be interface. You express that at the node type with can-update: interface '<imported interfaces id>'.

interfaces
	'Supplier' = .'Supplier Data'

root {
	'Supplier Data': group {
		can-update: interface 'Supplier'

		'Delivery Time': number 'days'
	}
}

'imported interfaces': [ interfaces ] dictionary {
	'path': [ = ] component 'descendant node path'
}

The `root` node type

Alan models are hierarchical models specifying hierarchical data. An Alan model is a hierarchy of nested types with a single root type:

root { }

The root type (short for node type) is a complex type that nests other (complex) types. Types are surrounded by curly braces, and their identification is a path which starts from the root type. We refer to an instance of a type as a node. The rule for defining a type carries the same name: node; it should be read as the node type rule, as we define node types in a model (for legacy reasons it is called the 'node' rule).

'root': [ root ] component 'node'

Numerical types

Numbers in an application model require a numerical type. Also, computations with numbers of different numerical types require conversion rules. Divisions require a division conversion rule, products require a product conversion rule, and so on. Some examples of numerical types, with conversion rules are

'date' in 'days' @date
'date and time' in 'seconds' @date-time
'days'
'milliseconds'
	= 'seconds' * 1 * 10 ^ 3 // rule for converting 'seconds' to milliseconds
	@numerical-type: (
		label: "sec"
		decimals: 3
	)
'minutes' @duration: minutes
'seconds'
	= 'seconds' * 'factor' // 'seconds' times a 'factor' produces 'seconds'
	= 'seconds' / 'factor'
	= 'milliseconds' * 1 * 10 ^ -3
	= 'minutes' * 60 * 10 ^ 0
	@duration: seconds
'factor'
	= 'factor' * 'factor'
	= 'seconds' / 'seconds'

Annotations like @date map numerical types to formats for easy modification in the GUI. With @factor you can present 1000 milliseconds as 1 second to the application user.
If you do so, be sure to set @label: to "sec" as well!

'numerical types': [ numerical-types ] dictionary {
	'type': stategroup (
		'relative' {
			'timer resolution': stategroup (
				'none' { }
				'seconds' { [ : time-in-seconds ] }
			)
			'range type': [ in ] reference
		}
		'absolute' {
			'product conversions': dictionary { [ = ]
				'right': [ * ] reference
			}
			'division conversions': dictionary { [ = ]
				'denominator': [ / ] reference
			}
		}
	)
	'singular conversions': dictionary { [ = ]
		'type': stategroup (
			'factor' {
				'invert': stategroup (
					'no' { [ * ] }
					'yes' { [ / ] }
				)
				'factor': integer
				'base': [ * ] integer
				'exponent': [ ^ ] integer
			}
			'base' {
				'offset': [ + ] integer
				'base': [ * ] integer
				'exponent': [ ^ ] integer
				'unit conversion': stategroup (
					'no' { }
					'yes' {
						'conversion rule': [ in ] reference
					}
				)
			}
		)
	}
	'ui': component 'ui numerical type'
}

Node types

Node types contain a permissions definition for controlling read and update permissions, a todo definition to mark a node as a todo-item, and attributes. An attribute is of type property, reference-set, command, or action.

Property attributes

A property specifies a part of the data structure. Alan supports six different property types: text, file, number, collection, stategroup, and group.

Text, file, and number are primitive property types. Text properties hold an unbounded string value. File properties hold two unbounded string values: a file token and a file extension. Number properties hold an integer value, with an optional positive annotation to ensure values greater zero. For ensuring that number values have a predefined accuracy, Alan does not support number values with a fractional component. For expressing the accuracy of a number, number properties reference a numerical type.

'Name'        : text
'Price'       : number 'euro'
'Release Date': number positive 'date and time'

A collection property holds a map of key-value pairs. Keys are text values that have to be unique such that we can reference them unambiguously. A key field has to be specified explicitly, after the keyword collection; values are nodes of an inline defined type that specifies the key field:

Customers : collection ['Customer ID'] {
	'Customer ID': text
	... /* other attributes of this type */ ...
}

A state group property holds a value indicating a state. States are the alternatives to an aspect that a state group property indicates. For example, red, orange, or green for a color property of a traffic light. The type of the property value corresponds to one out of multiple predefined state types, such as simple or assembled:

'Product Type': stategroup (
	'Simple' { ... /* attributes of this type */ ... }
	'Assembled' { ... /* attributes of this type */ ... }
)

A group property groups related property values, which is useful for presentational purposes:

'Address': group {
	'City': text
	'State': text
	'Zip Code': text
}

Derived values. Properties hold either base values or derived values (derivations). Derived values are computed from base values and other derived values. Application users cannot modify derived values. Properties holding derived values require an expression for computing their values at runtime:

'City': text					// property holding a base value
'copy of City': text = .'City'  // property with an expression for deriving its value

The derivations section provides the grammar for derivation expressions, detailing the different types of computations that the language supports.

Presentation options. The ui component properties reference GUI annotation rules for tweaking and tuning the behaviour and presentation of properties in the generated GUI. Some examples of GUI annotations are

@hidden: hides a derived property from the UI.
@description: "a description": describes the property in more detail to the user. Useful in combination with validation rules!
@validate: "[a-b]+": sets a regex for text properties that defines what values are acceptable.
@min: and @max:: limits number values.
@identifying: marks a property to always be displayed in addition to an collection entry’s key.
@default: 'Assembled': specifies a default state for a state group property.
@default: today|now: sets date or date-time number value to the current time.
@default: guid: initializes a text property with a generated unique id string.
@small: displays (small) collections inline, and includes them when pressing ‘Duplicate’.
@multi-line: presents a multi-line text area for a text property.

Reference set attributes

A reference-set is for creating bidirectional references. A reference set attribute holds the inverse of a reference which is by default unidirectional. References determine the values for reference sets; they create inverse references when your model specifies it. Derivation expressions refer to them for computations (e.g. derived numbers).

Command attributes

A command is a complex parametrized atomic operation on the dataset. The application engine executes a command in a single transaction. A command attribute specification consists of a definition of parameters for the command and an implementation.

Action attributes

An action is a sequence of operations that a webclient (GUI) executes. That is, unlike a command, an action can perform multiple different operations, interactively. Actions provide users with wizards to guide them through their processes. For an action, you can specify parameters that users have to provide before starting the execution of the action. After the parameters, you have specify which operations should be performed.

'node' { [ {, } ]
	'permissions definition': component 'node permissions definition'
	'todo definition': component 'todo definition'
	'has attributes': stategroup = node-switch .'attributes' (
		| nodes = 'yes' {
			'first' = first
			'last' = last
		}
		| none  = 'no'
	)
	'attributes': dictionary {
		'has predecessor': stategroup = node-switch predecessor (
			| node = 'yes' { 'attribute' = predecessor }
			| none = 'no'
		)
		'has successor': stategroup = node-switch successor (
			| node = 'yes' { 'attribute' = successor }
			| none = 'no'
		)
		'type': stategroup (
			'reference set' { [ : reference-set ]
				'referenced type path': group { [ -> ]
					'evaluation': component 'evaluation phase annotation'
					'head': component 'ancestor attribute path'
					'root type': stategroup (
						'simple' { }
						'sibling' { [ sibling ] }
					)
					'tail': component 'plural descendant node path'
				}
				'value source': [ = ] stategroup (
					'reference' {
						'reference': [ inverse ] component 'entry reference selector'
					}
					'union branch' {
						'branch': [ branch ] reference
					}
				)
			}
			'command' { [ : command ]
				'type': stategroup (
					'global' {
						'ui': component 'ui command attribute'
					}
					'component' { [ component ] }
				)
				'permission definition': component 'command permission definition'
				'parameters': component 'node'
				'implementation': stategroup (
					'external' { [ external ] }
					'internal' {
						'implementation': component 'command'
					}
				)
			}
			'action' { [ : action ]
				'parameters': component 'node'
				'action': component 'ui action'
			}
			'property' { [ : ]
				'type': stategroup (
					'group' { [ group ]
						'type': stategroup (
							'base' { }
							'derived' { [ = ] }
						)
						'ui': component 'ui group property'
						'node': component 'node'
					}
					'collection' { [ collection ]
						'key property': [ [, ] ] reference
						'type': stategroup (
							'base' {
								'graph constraints': component 'graph constraints definition'
							}
							'derived' { [ = ]
								'evaluation': component 'explicit evaluation annotation'
								'key constraint': stategroup (
									'no' {
										'branches': [ flatten (, ) ] dictionary {
											'expression': [ = ] component 'flatten expression'
											'variable assignment': component 'optional named object assignment'
											'node initializer': component 'node initializer'
										}
										'separator': [ join ] stategroup (
											'dot' { [ . ] }
											'dash' { [ - ] }
											'colon' { [ : ] }
											'greater than' { [ > ] }
											'space' { [ space ] }
										)
									}
									'yes' {
										'expression': component 'plural reference expression'
									}
								)
							}
						)
						'permissions': component 'item permissions definition'
						'ui': component 'ui collection property'
						'node': component 'node'
					}
					'number' { [ number ]
						'set type': stategroup (
							'integer' { }
							'natural' { [ positive ] }
						)
						'numerical type': reference
						'type': stategroup (
							'base' {
								'type': stategroup (
									'causal' {
										'type': stategroup (
											'mutation' { [ = mutation-time ]
												'watched property': [ . ] reference
											}
											'creation' { [ = creation-time ] }
											'destruction' {
												'destruction operation': stategroup (
													'set to lifetime' { [ = life-time ] }
													'add lifetime' { [ add life-time ] }
													'subtract lifetime' { [ subtract life-time ] }
												)
												'watched stategroup': [ . ] reference
												'watched state': [ ? ] reference
											}
										)
									}
									'simple' {
										'metadata recording': component 'metadata recording'
									}
								)
							}
							'derived' { [ = ]
								'value source': stategroup (
									'parameter' { [ parameter ] }
									'expression' {
										'evaluation': component 'explicit evaluation annotation'
										'expression': component 'derivation expression'
									}
								)
							}
						)
						'behaviour': stategroup (
							'none' { }
							'timer' { [ timer ontimeout ]
								'implementation': component 'command'
							}
						)
						'ui': component 'ui number property'
					}
					'file' { [ file ]
						'type': stategroup (
							'base' {
								'metadata recording': component 'metadata recording'
							}
							'derived' { [ = ]
								'value source': stategroup (
									'parameter' { [ parameter ] }
									'expression' {
										'evaluation': component 'explicit evaluation annotation'
										'expression': component 'derivation expression'
									}
								)
							}
						)
						'ui': component 'ui file property'
					}
					'text' { [ text ]
						'has reference': stategroup (
							'no' { }
							'yes' {
								'behaviour': component 'reference behaviour'
								'expression': component 'entry reference definition'
								'rules': dictionary { [ where ]
									'has predecessor': stategroup = node-switch predecessor (
										| node = 'yes' { 'rule' = predecessor }
										| none = 'no'
									)
									'type': stategroup (
										'optional entry reference' { [ ~> ]
											'expression': component 'entry reference definition'
										}
										'node reference' {
											'behaviour': component 'reference behaviour'
											'path': group {
												'context': stategroup (
													'referenced node' { [ $ ] }
													'sibling rule' {
														'rule': reference
													}
												)
												'node path': component 'object path tail'
											}
										}
									)
								}
							}
						)
						'type': stategroup (
							'base' {
								'metadata recording': component 'metadata recording'
							}
							'derived' { [ = ]
								'value source': stategroup (
									'parameter' { [ parameter ] }
									'derived key' { [ key ] }
									'expression' {
										'evaluation': component 'explicit evaluation annotation'
										'expression': component 'derivation expression'
									}
								)
							}
						)
						'ui': component 'ui text property'
					}
					'state group' { [ stategroup ]
						'type': stategroup (
							'base' { }
							'derived' { [ = ]
								'value source': stategroup (
									'parameter' { [ parameter ] }
									'expression' {
										'evaluation': component 'explicit evaluation annotation'
										'expression': component 'derivation expression'
									}
								)
							}
						)
						'ui': component 'ui state group property'
						'first state': reference = first
						'states': [ (, ) ] dictionary {
							'has successor': stategroup = node-switch successor (
								| node = 'yes' { 'successor' = successor }
								| none = 'no'
							)
							'record lifetime': stategroup (
								'yes' { [ life-time ]
									'meta property': [ = . ] reference
									'creation timestamp': [ from ] reference
								}
								'no' { }
							)
							'rules': dictionary { [ where ]
								'has predecessor': stategroup = node-switch predecessor (
									| node = 'yes' { 'rule' = predecessor }
									| none = 'no'
								)
								'behaviour': component 'reference behaviour'
								'path': group {
									'context': stategroup (
										'this node' {
											'evaluation': component 'explicit evaluation annotation'
											'head': component 'context object step'
										}
										'sibling rule' {
											'rule': reference
										}
									)
									'node path': component 'object path tail'
								}
							}
							'permissions': component 'item permissions definition'
							'ui': component 'ui state'
							'node': component 'node'
						}
					}
				)
			}
		)
	}
}

References

References indicate relations between different parts of your application data. For example, suppose that you have Orders and Products, where Orders reference a Product. You can express that reference in your model, such that your users can see it, and such that you can use it in computations:

'Products': collection ['Name'] {
	'Name': text
	'In Stock': stategroup (
		'No' { }
		'Yes' { }
	)
}
'Orders': collection ['ID'] {
	'ID': text
	'Product': text -> ^ .'Products'[]          // reference rule for text
		where 'In Stock' -> $ .'In Stock'?'Yes' // additional reference rule for the text
	'Ready': stategroup (
		'No' { }
		'Yes' { }
	)
	'Sent for Delivery': stategroup (
		'No' { }
		'Yes' where 'Order Ready' -> .'Ready'?'Yes' { } // reference rule for state
	)
}

The example indicates that you can specify multiple references at a text property. You can also specify additional rules for the ‘main’ reference with keyword $, which refers to the referenced node.

In order for the text value to reference an item in a collection, its value has to equal the key value of an item in the specified collection. At runtime, reference expressions always produce a single specific node (or none at all, if the reference is broken). The language ensures that. In the GUI, references translate to a select list from which the application user has to choose an item.

Alternatively, sometimes a specific state for a state group is related to another node. The where-rule Order Ready expresses that: an order can be Sent for Delivery if and only if it is Ready.

Reference behaviour

The reference behaviour that you specify, determines how the runtime treats a reference. Mandatory references (specified with keyword ->) are constraints that are enforced by the runtime: they have to resolve to a node. Optional references (specified with keyword ~>) do not have to resolve to a node.

'reference behaviour' {
	'type': stategroup (
		'mandatory' { [ -> ] }
		'optional' { [ ~> ] }
	)
}

The language ensures that references either point to a single specific node, or none at all. Thus, mandatory references unambiguously point to a single specific node. Because of that, derived value computations and command invocations can safely use them.

Optional references are especially useful when you want user data to reference imported data (can-update: interface '...'). Mandatory references are not allowed among data from different sources, such that data import is always successfull.

Upstream & downstream

Reference constraint expressions exist in two different flavours: (1) upstream reference expressions that use earlier defined attributes and (2) downstream reference expressions that freely use earlier and later defined attributes. Downstream references require an explicit annotation: downstream after the arrow (->/~>) specifying the reference behaviour.

The runtime evaluates references in a predefined order in several different phases. The order and the different phases ensure that resolution can be done deterministically, and in such a way that references do not depend on other unresolved references. First, mandatory upstream references are resolved. Then, mandatory downstream references are resolved. For that reason, mandatory upstream references cannot depend on mandatory downstream references.

Optional references follow a similar approach, but are evaluated in separate phases. That is because they are only used for derived values, as the runtime does not enforce them.

'evaluation phase annotation' {
	'phase': stategroup (
		'upstream' { }
		'downstream' { [ downstream ] }
	)
}

'explicit evaluation annotation' {
	'phase': component 'evaluation phase annotation'
	'sibling navigation': stategroup (
		'no' { }
		'yes' { [ (, ) ]
			'graph traversal': [ sibling ] stategroup (
				'no' { }
				'yes' { [ in ]
					'traversal type': stategroup (
						'base order' { }
						'inverse order' { [ inverse ] }
					)
					'ancestor path': component 'ancestor node path'
					'graph': reference
				}
			)
		}
	)
}

Below we explain the annotation for sibling navigation.

Bidirectional references

Text references are either unidirectional or bidirectional. For bidirectional references, you specify a reference-set. If a reference is downstream reference, then the reference-set holds upstream references. Conversely, if a reference is upstream, then the reference-set holds downstream references:

'Products': collection ['Name'] {
	'Name': text
	// reference-set holding downstream references to Orders added by Product references,
	'Orders': reference-set -> downstream ^ .'Orders'* = inverse >'Product'
}
'Orders': collection ['ID'] {
	'ID': text
	// a (bidirectional) upstream reference:
	'Product': text -> ^ .'Products'[] -<'Orders'
}

The expression ^ .'Products' is a navigation expression that produces exactly one collection at runtime. The Alan runtime interpretes such navigation expressions as follows: starting from the Orders node, go to the parent node (as expressed by the navigation step ^); then select the Products collection found on that node. Thus, at runtime, navigation expressions are executed relative to the context node for which the expression should be evaluated.

Sibling references

If you want references from Products to other Products, you will find that this line gives an error:

`Other Product`: text -> ^ .'Products'[]

The compiler requires that you reference an earlier defined property, and not the Products property that defines the expression. For references from Products to other other Products, you need special sibling references.

'entry reference definition' {
	'evaluation': component 'explicit evaluation annotation'
	'type': stategroup (
		'simple' {
			'head': component 'context object step'
			'collection path': [, [] ] component 'object path tail'
		}
		'sibling' {
			'context': stategroup (
				'operation' { [ @ ] }
				'dataset' { }
			)
			'ancestor path': component 'ancestor node path'
			'graph participation': [ sibling ] stategroup (
				'no' {
					'support self reference': stategroup (
						'no' { }
						'yes' { [ || self ] }
					)
				}
				'yes' { [ in ]
					'graph': [ (, ) ] reference
				}
			)
		}
	)
	'tail': component 'descendant object path'
	'inversion': stategroup (
		'no' { }
		'yes' { [ -< ]
			'reference set': reference
		}
	)
}

The following model expresses sibling references from Products to other Products which are corresponding (Parts), and also from Orders to a Previous Order:

'Products': collection ['Name']
	'assembly': acyclic-graph
{
	'Name': text
	'Parts': collection ['Product'] {
		// an 'upstream' sibling Product reference that partakes in the 'assembly' graph:
		'Product': text -> ^ sibling in ('assembly')
		'Part Price': number 'euro'
			= ( sibling in ^ 'assembly' ) >'Product'.'Product Price'
	}
	'Product Price': number 'euro'
		= ( sibling in 'assembly' ) sum .'Parts'* .'Part Price' // recursion!
}
'Orders': collection ['Year']
	'timeline': ordered-graph .'Is First Order' ( ?'Yes'|| ?'No'>'Previous Order' )
{
	'Year': text
	'Price': number 'euro'
	'Is First Order': stategroup (
		'Yes' { }
		'No' {
			'Previous Order': text -> ^ sibling in ('timeline')
		}
	)
	'Total Sales Value': number 'euro' = ( sibling in 'timeline' ) switch .'Is First Order' (
		|'Yes' => .'Price'
		|'No' as $'no' => sum (
			.'Price',
			$'no'>'Previous Order'.'Total Sales Value' // recursion!
		)
	)
}

Graph constraints

The model above also expresses graph constraints. Graph constraints ensure termination for recursive computations traversing a graph. Graph constraints ensure that a set of references (edges) together form a graph satisfying a specific property. For example, an acyclic-graph constraint ensures that references that partake in the graph, form a directed acyclic graph. For a detailed explanation, see AlanLight.

'graph constraints definition' {
	'graphs': dictionary {
		'type': [ : ] stategroup (
			'acyclic' { [ acyclic-graph ] }
			'ordered' { [ ordered-graph ]
				'ordering property path': group {
					'ordering state group path': component 'descendant property path'
					'ordering states': [ (, ) ] group {
						'sink state': [ ? ] reference
						'edge state': [ || ? ] reference
						'edge reference': [ > ] reference
					}
				}
			}
		)
	}
}

The example model expresses that Products form an acyclic assembly graph via their Parts: Product references of Parts partake in the acyclic assembly graph on Products. The constraint ensures that recursive Product Price computations terminate.

For orders, the model expresses an ordered timeline graph, which means that a strict total ordering exists for all Orders. That is: only one Orders item does not have preceding Order. All other Orders do. For ordered graphs, the application language supports deriving the source and the sink of the graph: the first Order and the most recent Order.

Note that the Product Price expression starts with an annotation: ( sibling in 'assembly' ). When you want to use a sibling reference in a computation, you have to provide the ( sibling ) annotation. In order to succesfully compile recursive computations, you have to add the in 'assembly' part, such that the compiler knows that an acyclic graph will be traversed. That is: that the computation is guaranteed to be finite.

Sometimes, computations traverse the inverse of a graph (by using a reference-set attribute). For such computations, you need to add the annotation inverse: ( sibling in inverse 'assembly' ).

Derived values

Derived values (derivations) are computed from base values and other derived values. The application language supports derived texts, numbers, files, states, references, and collections. Derived texts, numbers, files, states, and references share common grammar rules: the derivation expression rule and corresponding parts presented below. The language has special rules for deriving collections.

Upstream, downstream, and sibling dependence

In the references section we already discussed upstream, downstream, and sibling references. A reference is a downstream reference or has a sibling (node of the same type) dependency when the model expresses that with an annotation. The annotations are part of our solution for ensuring termination of derived value computations, without needing the compiler to do complex analyses. It also requires you to think about the flow of data through your application, which we think leads to more well-structured data models.

In summary, computations are divided over the following four different phases:

upstream constraints (mandatory upstream references)
downstream constraints (mandatory downstream references)
upstream derivations
downstream derivations

During both upstream phases, the runtime traverses your model from top to bottom. During the downstream phases, the runtime traverses your model in a compiler-optimized order.

NOTE: the order of properties in your model is important to the compiler: application models are ordered data models!

Computations that are evaluated in a specific phase, can depend on all computations from an earlier phase. So, computations from phase 4 can depend on computations evaluated in all preceding phases. Furthermore, as the runtime traverse your model from top to bottom during phase 1, computations for properties specified at the top of your model will be done before later defined property values. You can therefore depend on values that are computed in an identical phase as well, as long as it satisfies the corresponding upstream/downstream order:

'A': text = .'B' //ERROR: using later defined 'B' in the upstream derivations phase
'B': text = .'A' //OK:    using earlier defined 'A' in the upstream derivations phase

The annotation ( sibling ) is required when you want to use a sibling reference in a computation. For recursive computations, you need to specify which (acyclic) graph the computation traverses, such that termination is guaranteed, as shown in the sibling references example.

Expressions

A derivation expression starts with optional switch statements followed by a subexpression that produces a value. The following code sample exemplifies the use of the different types of switch statements, where each case produces a text value:

'Orders': collection ['Order'] {
	'Order': text
	'Price': number 'euro'
}
'Store Status': stategroup (
	'Open' { }
	'Closed' { }
)

/* state switch */
'Store Status Label': text = switch .'Store Status' (
	|'Open'   => "Open"
	|'Closed' => "Closed"
)

/* node switch */
'Favorite Order': text ~> .'Orders'[]
'Favorite Order Exists?': text = switch >'Favorite Order' (
	| none => "No"
	| node => "Yes"
)

/* node set switch */
'How Many Orders?': text = switch .'Orders'* (
	| none  => "No Orders"
	| node  => "One Order"
	| nodes => "More Than One Order"
)

/* number switch */
'Order Count': number 'count' = count .'Orders'*
'More Than 10 Orders?': text = switch .'Order Count' compare ( 10 ) (
	| >  => "More than 10"
	| <  => "Less than 10"
	| == => "Exactly 10"
)

'derivation expression' {
	'type': stategroup (
		'produce value' {
			'expression': component 'derivation expression tail'
		}
		'state switch' { [ switch ]
			'state group path': component 'singular variablized object path'
			'states': [ (, ) ] dictionary { [ | ]
				'variable assignment': component 'optional named object assignment'
				'expression': [ => ] component 'derivation expression'
			}
		}
		'node switch' { [ switch ]
			'node path': component 'variablized object path'
			'operation': stategroup (
				'equality' {
					'other node path': [ is (, ) ] component 'singular variablized object path'
				}
				'existence' { }
			)
			'cases': [ (, ) ] group { dynamic-order
				'node': group { [ | node ]
					'variable assignment': component 'optional named object assignment'
					'expression': [ => ] component 'derivation expression'
				}
				'none': [ | none => ] component 'derivation expression'
			}
		}
		'set switch' { [ switch ]
			'nodes path': component 'object set path'
			'cases': [ (, ) ] group { dynamic-order
				'match none': stategroup (
					'no' { }
					'yes' { [ | none => ]
						'expression': component 'derivation expression'
					}
				)
				'match node': stategroup (
					'no' { }
					'yes' { [ | node ]
						'variable assignment': component 'optional named object assignment'
						'expression': [ => ] component 'derivation expression'
					}
				)
				'match nodes': stategroup (
					'no' { }
					'yes' { [ | nodes ]
						'variable assignment': component 'optional named object assignment'
						'expression': [ => ] component 'derivation expression'
					}
				)
			}
		}
		'number switch' { [ switch ]
			'number path': component 'singular variablized object path'
			'compare to': [ compare (, ) ] stategroup (
				'constant' {
					'value': component 'constant number value'
				}
				'path' {
					'right number path': component 'singular variablized object path'
				}
			)
			'last case': reference = last
			'cases': [ (, ) ] dictionary (
				static 'equals' [ == ]
				static 'less than or greater than' [ <> ]
				static 'greater than' [ > ]
				static 'greater than or equals' [ >= ]
				static 'less than' [ < ]
				static 'less than or equals' [ <= ]
			) { [ | ]
				'has predecessor': stategroup = node-switch predecessor (
					| node = 'yes' { 'case' = predecessor }
					| none = 'no'
				)
				'variable assignment': component 'optional named object assignment'
				'expression': [ => ] component 'derivation expression'
			}
		}
	)
}

'derivation expression list' {
	'head': component 'derivation expression tail'
	'has tail': stategroup (
		'no' { }
		'yes' { [ , ]
			'tail': component 'derivation expression list'
		}
	)
}

'derivation expression tail' {
	'type': stategroup (
		'reference' {
			'type': stategroup (
				'branch' // branch of derived collection constructed using flatten expressions
				{
					'branch': [ branch ] reference
					'expression': [ [, ] ] component 'singular variablized object path'
				}
				'ordered graph node' {
					'type': stategroup (
						'source' { [ source-of ] }
						'sink' { [ sink-of ] }
					)
					'collection path': component 'singular variablized object path'
					'ordered graph': [ in ] reference
				}
			)
		}
		'text' {
			'type': stategroup (
				'static' {
					'value': text
				}
				'concatenation' { [ concat (, ) ]
					'expression': component 'derivation expression list'
				}
			)
		}
		'number' {
			'expression': component 'number expression'
		}
		'state' {
			'initializer': component 'state initializer'
		}
		'dynamic' {
			'path': component 'singular variablized object path'
		}
	)
}

Derived texts

A derived text value can consist of static text values and text values from other properties:

'Address': group {
	'Street'       : text // e.g. "Huntington Rd"
	'Street number': text // e.g. "12B"
}
// label for an external billing system, like "Huntington Rd 12B":
'Address label': text = concat ( .'Address'.'Street', " ", .'Address'.'Street number' )

Derived numbers

Examples of derived number properties, including required conversion rules:

root {
	'Tax Percentage': number positive 'percent'
	'Products': collection ['Name'] {
		'Name': text
		'Price': number 'eurocent'
		'Price (euro)': number 'euro' = from 'eurocent' .'Price'
		'Order Unit Quantity': number positive 'items'
		'Orders': reference-set -> downstream ^ .'Orders'* = inverse >'Product'
		'Sales Value': number 'eurocent' = downstream sum <'Orders'* .'Price'
		'Items Sold': number 'items' = count <'Orders'*
	}
	'Total Sales Value': number 'eurocent' = downstream sum .'Products'* .'Sales Value'
	'Number of Products': number 'items' = count .'Products'*
	'Orders': collection ['ID'] {
		'ID': text
		'Product': text -> ^ .'Products'[] -<'Orders'
		'Quantity': number positive 'items'
		'Loss': number 'items' = remainder (
			.'Quantity',
			>'Product' .'Order Unit Quantity'
		)
		'Price': number 'eurocent' = product (
			>'Product'.'Price' as 'eurocent',
			.'Quantity'
		)
		'Order Units': number positive 'units' = division ceil (
			.'Quantity' as 'items' ,
			>'Product'.'Order Unit Quantity'
		)
		'Tax': number 'eurocent'
		'Gross Price': number 'eurocent' = sum ( .'Price', .'Tax' )
		'Creation Time': number 'date and time'
		'Estimated Lead Time': number 'seconds'
		'Estimated Delivery Time': number 'date and time' = add (
			.'Creation Time',
			.'Estimated Lead Time' )
		'Delivered': stategroup (
			'No' { }
			'Yes' {
				'Delivery Time': number positive 'date and time'
				'Lead Time': number 'seconds' = diff 'date and time' (
					.'Delivery Time',
					^ .'Creation Time'
				)
			}
		)
	}
	'Gross Income': number 'eurocent' = sum .'Orders'* .'Gross Price'
}
numerical-types
	'percent'
	'euro'
		= 'eurocent' * 1 * 10 ^ -2
	'eurocent'
		= 'eurocent' * 'items'
	'units'
		= 'items' / 'items'
	'items'
	'date and time' in 'seconds'
	'seconds'

'number expression' {
	'type': stategroup (
		'unary' {
			'type': stategroup (
				'constant' {
					'value': component 'constant number value'
				}
				'numerical type conversion' {
					'conversion': [ from ] reference
					'expression': component 'derivation expression tail'
				}
				'sign inversion' { [ - ]
					'expression': component 'derivation expression tail'
				}
			)
		}
		'aggregate' {
			'type': stategroup (
				'collection operation' {
					'type': stategroup (
						'property' {
							'operation': stategroup (
								'minimum' { [ min ] }
								'maximum' { [ max ] }
								'sum' { [ sum ] }
								'standard deviation' { [ std ] }
							)
							'numbers path': component 'object set path'
						}
						'count' { [ count ]
							'nodes path': component 'object set path'
						}
					)
				}
				'remainder' { [ remainder (, ) ]
					'numerator': component 'unary number expression'
					'denominator': [ , ] component 'unary number expression'
				}
				'division' { [ division ]
					'rounding': stategroup (
						'ordinary' { }
						'ceil' { [ ceil ] }
						'floor' { [ floor ] }
					)
					'expressions': [ (, ) ] group {
						'numerator': component 'unary number expression'
						'conversion rule': [ as ] reference
						'denominator': [ , ] component 'unary number expression'
					}
				}
				'product' { [ product (, ) ]
					'left': component 'unary number expression'
					'conversion rule': [ as ] reference
					'right': [ , ] component 'unary number expression'
				}
				'list operation' {
					'operation': stategroup (
						'sum' { [ sum ] }
						'maximum' { [ max ] }
						'minimum' { [ min ] }
					)
					'numbers': [ (, ) ] component 'derivation expression list'
				}
				'addition' { [ add (, ) ]
					'left': component 'unary number expression'
					'right': [ , ] component 'unary number expression'
				}
				'difference' { [ diff ]
					'relative numerical type': reference
					'expressions': [ (, ) ] group {
						'left': component 'unary number expression'
						'right': [ , ] component 'unary number expression'
					}
				}
			)
		}
	)
}

'unary number expression' {
	'expression': component 'derivation expression tail'
}

'constant number value' {
	'value': integer
}

Derived files

Derived file values take their value (token + extension) from another file value. For example, you can derive a Contract which is a Default Contract in case of a Standard Agreement, and a Custom Contract in case of a Custom Agreement:

'Standard Contract': file
'Agreement': stategroup (
	'Standard' { }
	'Custom' {
		'Contract': file
	}
)
'Contract': file = switch .'Agreement' (
	|'Standard' => .'Standard Contract'
	|'Custom' as $'con'  => $'con'.'Contract'
)

Derived states

Derived states are computed using the abovementioned switch expressions, where different cases lead to different states. For example, we can derive if a Product exists in a Catalog of Products from a Catalog Provider. For this purpose, we check if the optional Product reference on an Order produces a node or nothing:

'Catalog': group { can-update: interface 'Catalog Provider'
	'Products': collection ['Name'] {
		'Name': text
		'Price': number 'eurocent'
		'Description': text
	}
}
'Orders': collection ['ID'] {
	'ID': text
	'Product': text ~> ^ .'Catalog'.'Products'[]
	'Product found': stategroup = switch >'Product' (
		| node as $ => 'Yes' where 'Found Product' = $ ( 'Price' = $ .'Price' )
		| none => 'No' ( )
	) (
		'Yes' where 'Found Product' -> >'Product' {
			'Description': text = .&'Found Product'.'Description'
			'Price': number 'eurocent' = parameter
		}
		'No' { }
	)
}

The expression for deriving a state, has to satisfy all where rules for the state. In the example, the where rule expresses that the optional Product reference is no longer optional. Instead, the reference is mandatory in context of the Yes state. The expression ‘proves’ that. You can use the Found Product for deriving values such as Description on the state node.

An expression for deriving a state can express how to initialize property values of the state as well, such as Price in the example. To make this work, you have to specify = parameter for properties that you want to set with the state initializer. This language construct is especially useful when a reference to a node like 'Found Product' is not available. Furthermore, it useful for special operations such as source-of and sink-of, which we discuss below.

'state initializer' {
	'state': reference
	'rule arguments': dictionary { [ where ]
		'path': [ = ] component 'singular variablized object path'
	}
	'node initializer': component 'node initializer'
}

'node initializer' {
	'arguments': [ (, ) ] dictionary {
		'expression': [ = ] component 'derivation expression'
	}
}

Derived references

Sometimes it is useful to derive a reference to a collection entry for use by the application user and other computations. Similar to base references, derived references require you to express a text property follow by a reference definition. For deriving a reference, you have to provide an expression that produces a node that matches the reference definition. The definition of 'Product copy' depicts that:

'Products': collection ['Name'] {
	'Name': text
}
'Orders': collection ['Year']
	'timeline': ordered-graph .'Is First Order' ( ?'Yes'|| ?'No'>'Previous Order' )
{
	'Year': text
	'Product': text -> ^ .'Products'[]
	'Product copy': text -> ^ .'Products'[] = >'Product' /* derived reference */
	'Is First Order': stategroup (
		'Yes' { }
		'No' {
			'Previous Order': text -> ^ sibling in ('timeline')
		}
	)
}

/* source-of/sink-of of graph */
'Has Orders': stategroup = switch .'Orders'* (
	| nodes as $ => 'Yes' (
		'Oldest Order' = sink-of $ in 'timeline'
		'Most Recent Order' = source-of $ in 'timeline'
	)
	| none => 'No' ( )
) (
	'Yes' {
		'Oldest Order'     : text -> ^ .'Orders'[] = parameter /* derived reference */
		'Most Recent Order': text -> ^ .'Orders'[] = parameter /* derived reference */
	}
	'No' { }
)

With the special source-of and sink-of operation, you can derive a reference to the respective nodes in an ordered graph. These operations can only be applied to a collection for which we can guarantee non-emptiness, as otherwise the source/sink do not exist. Therefore, we first switch on the content of the 'Orders' collection. If it holds nodes (meaning that it is not empty), then we can apply the source-of and sink-of operations.

Derived collections

'flatten expression' {
	'head': component 'group ancestor path'
	'path': component 'plural descendant node path'
}

'plural reference expression' {
	'type': stategroup (
		'augment' {
			'collection path': component 'singular variablized object path'
			'filter path': [ * ] component 'descendant object path'
		}
		'union' { [ union ]
			'branches': [ (, ) ] dictionary {
				'has predecessor': stategroup = node-switch predecessor (
					| node = 'yes' { }
					| none = 'no'
				)
				'has successor': stategroup = node-switch successor (
					| node = 'yes' { }
					| none = 'no'
				)
				'expression': [ = ] component 'flatten expression'
				'dependency': component 'dependency step'
				'inversion': stategroup (
					'no' { }
					'yes' {
						'reference set': [ -< ] reference
					}
				)
			}
		}
	)
}

'plural descendant node path' {
	'has steps': stategroup (
		'no' { }
		'yes' {
			'property': component 'property step'
			'value type': stategroup (
				'choice' {
					'state': [ ? ] reference
				}
				'node' { }
				'collection' { [ * ] }
			)
			'tail': component 'plural descendant node path'
		}
	)
}

Permissions and Todos

The application language supports expression permission and todo requirements down to the level of a single specific user or interface. At the node type level you can specify permissions for nodes: read and update permissions. In addition, you can express that a node creates a todo-item in a todo-list of your application. At collection properties and states, you can specify item permissions: create and delete permissions for collection entries and states. At command attributes you can express permission requirements for executing a command.

'node permissions definition' { dynamic-order
	'read permission': stategroup (
		'inherited' { }
		'explicit' { [ can-read: ]
			'permission': component 'permission'
		}
	)
	'update permission': stategroup (
		'inherited' { }
		'explicit' { [ can-update: ]
			'permission': component 'permission'
		}
	)
}

'item permissions definition' { dynamic-order
	'create permission': stategroup (
		'inherited' { }
		'explicit' { [ can-create: ]
			'permission': component 'permission'
		}
	)
	'delete permission': stategroup (
		'inherited' { }
		'explicit' { [ can-delete: ]
			'permission': component 'permission'
		}
	)
}

'permission' {
	'source': stategroup (
		'user' {
			'requirement': component 'user requirement'
		}
		'imported interface' {
			'interface': [ interface ] reference
		}
	)
}

Permissions

When read permissions and update permissions are not specified at the root node type, all application users can read and update all application data. Thus, if your applications supports anonymous users, anyone with your application’s url can access all application data.

To restrict access to your application data, you can start by specifying some permissions at the root node type. The line can-read: user at the root expresses that only users with a user account (in the Users collection), have access to application data:

root {
	can-read: user
	can-update: user .'Type'?'Admin'

	'Users': collection ['ID']
		can-create: user .'Type'?'Admin'
		can-delete: user .'Type'?'Admin'
	{
		can-read: user is ( /*this*/ ) || user .'Type'?'Admin'
		can-update: user .'Type'?'Admin' // NOTE: unneeded

		'ID': text
		'Address': group { can-update: ^ is ( user )
			'Street': text
			'City': text
		}
		'Type': stategroup (
			'Admin' { }
			'Employee' { }
			'Unknown' { has-todo: user .'Type'?'Admin' }
		)
	}
	// only team members can read team information:
	'Teams': collection ['Name'] { can-read: .'Members' [ user .'ID' ]
		'Name': text
		'Members': collection ['Member'] {
			'Member': text ~> ^ ^ .'Users'[]
		}
		'Description': text
	}
}

Node types inherit read and update permission requirements from their ancestor node types. That is, if you specify required permissions at the root node type, you do not have to repeat it a child node type. The child node type takes the permission requirements from the root node type.

Read permissions

Read permission requirements are cumulative. That is, in order to read a node, a user requires read permission for all ancestors nodes of that node as well. For example, in order to read a Members node specified above, a user needs permissions for the ancestor Teams-node, as well as the root node.

Update permissions

Update permission requirements are not cumulative. Instead, update permissions for child nodes override permission requirements for parent nodes. For example, for updates to the root node, we can require an admin: user .'Type'?'Admin'. If we were to omit other permission requirements, only admins would be able to update application data because of inheritance. But, because of can-update: ^ is ( user ) at Address in the model, users can (only!) update their own Address information.

NOTE: for updating a node, users have to be able to read ancestor nodes!

Create and delete permissions

Create and delete permission requirements for collection entries and states (items) inherit update permission requirements from the parent node type. The permissions are one-off overrides that are not carried down in the node type hierarchy. That is, they only apply to the state type or collection attribute where they are specified.

Command execution permissions

Command execution permissions are independent of aforementioned permissions. Execution permission requirements only apply to the command for which they are specified. If a command A calls another command B, then required permissions for B are not checked. That is, the application only verifies that the user is permitted to execute command A.

NOTE: for executing a command, the command has to be reachable, meaning that users need read access for the node on which they want to execute the command!

'command permission definition' {
	'execute permission': stategroup (
		'reachable' { }
		'explicit' { [ can-execute: ]
			'requirement': component 'user requirement'
		}
	)
}

Todo items

Todo items are shown in a special section of your generated application. The list of todo items is constructed from nodes that are marked as todos. You express that in your model with has-todo: followed by an expression that specifies to which users the todo item applies.

'todo definition' {
	'todo': stategroup (
		'no' { }
		'yes' { [ has-todo: ]
			'requirement': component 'user requirement'
			'ui': component 'ui todo'
		}
	)
}

User requirements

For user requirements you can depend on your application data via complex expressions that traverse your model. With the || keyword, you specify alternatives. With a where clause, you specify requirements on top of requirements (‘and’).

'user requirement' {
	'expression': component 'node expression'
	'has filter': stategroup (
		'no' { }
		'yes' {
			'assignment': component 'optional variable assignment'
			'path': [ where (, ) ] component 'user requirement'
		}
	)
	'has alternative': stategroup (
		'no' { }
		'yes' { [ || ]
			'alternative': component 'user requirement'
		}
	)
}

Commands and Timers

Commands enable external systems to perform operations via an Alan interface on application data. Furthermore, commands can perform operations on other systems that other systems provide via an Alan interface. For this to work, interfaces have to be listed in the interfaces section of an application model. Also, the external command needs to be consumed by the application model, like the Place Order command in the example:

'Products': collection ['Name'] {
	'Name': text
}
'Place Order': command { 'Product': text -> .'Products'[] } external
'Orders': collection ['ID'] {
	'ID': text
	'Product': text -> ^ .'Products'[]
	'Creation Time': number 'date and time' = creation-time
	'Status': stategroup (
		'New' {
			'Order from Manufacturer': command { }
				=> execute .'Place Order' ( 'Product' = ^ .'Product' )
				=> update ^ (
					'Status' = create 'Waiting for Manufacturer' ( )
				)
		}
		'Delivered' { }
		'Delayed' { }
		'Waiting for Manufacturer' {
			'Agreed Upon Delivery Time': number 'date and time'
				timer ontimeout => update ^ (
					'Status' = ensure 'Delayed' ( )
				)
		}
	)
}
// for external system 'Delivery Service':
'Register Delivery': command { 'Order': text -> .'Orders'[] }
	update @ >'Order' (
		'Status' = create 'Delivered' ( )
	)

'command object expression' {
	'properties': [ (, ) ] dictionary {
		'expression': [ = ] component 'command expression'
	}
}

'command object initialization behaviour' {
	'behaviour': stategroup (
		'ensure existence' { [ ensure ] }
		'fail when exists' { [ create ] }
	)
}

'command expression' {
	'operation': stategroup (
		'state switch' { [ switch ]
			'path': group {
				'path': component 'singular node path'
				'stategroup': [ . ] reference
			}
			'states': [ (, ) ] dictionary { [ | ]
				'variable assignment': component 'optional variable assignment'
				'expression': [ => ] component 'command expression'
			}
		}
		'node switch' { [ switch ]
			'expression': component 'node expression'
			'cases': [ (, ) ] group {
				'node case': [ | node ] group {
					'variable assignment': component 'optional variable assignment'
					'expression': [ => ] component 'command expression'
				}
				'none case': [ | none ] group {
					'expression': [ => ] component 'command expression'
				}
			}
		}
		'walk' { [ walk ]
			'path': component 'singular node path'
			'type': stategroup (
				'collection' {
					'collection': [ . ] reference
				}
				'reference set' {
					'reference set': [ < ] reference
				}
			)
			'has tail': stategroup (
				'no' { }
				'yes' { [ where ]
					'tail': component 'node path tail'
				}
			)
			'variable assignment': component 'optional variable assignment'
			'expression': [ (, ) ] component 'command expression'
		}
		'ignore' { [ ignore ] }
		'update properties' { [ update ]
			'path': component 'singular node path'
			'target': stategroup (
				'node' {
					'expression': component 'command object expression'
				}
				'property' {
					'property': [ . ] reference
					'expression': [ = ] component 'command expression'
				}
			)
		}
		'execute operation' { [ execute ]
			'path': component 'singular node path'
			'command': [ . ] reference
			'expression': component 'command object expression'
		}
		'produce value' {
			'value': stategroup (
				'object' {
					'expression': component 'command object expression'
				}
				'state' {
					'behaviour': component 'command object initialization behaviour'
					'state': reference
					'expression': component 'command object expression'
				}
				'scalar' {
					'expression': component 'scalar expression'
				}
				'empty collection' { [ empty ] }
				'current value' { [ current || ]
					'expression': component 'command expression'
				}
			)
		}
		'entry' {
			'type': stategroup (
				'create' {
					'behaviour': component 'command object initialization behaviour'
					'expression': component 'command object expression'
				}
				'delete' { [ delete ]
					'path': component 'singular node path'
				}
			)
		}
	)
}

'command' { [ => ]
	'expression': component 'command expression'
	'has next command': stategroup (
		'yes' {
			'command': component 'command'
		}
		'no' { }
	)
}

'user initializer' {
	'initializer': component 'command object expression'
}

'password initializer' {
	'initializer': component 'command object expression'
}

'identity initializer' {
	'initializer': component 'command object expression'
}

'scalar expression list' {
	'head': component 'scalar expression'
	'has tail': stategroup (
		'no' { }
		'yes' { [ , ]
			'tail': component 'scalar expression list'
		}
	)
}

'scalar expression' {
	'type': stategroup (
		'number' {
			'type': stategroup (
				'constant' {
					'value': component 'constant number value'
				}
				'now in seconds' { [ now ] }
				'unary expression' {
					'type': stategroup (
						'absolute value' { [ abs ] }
						'numerical type conversion' {
							'conversion': [ from ] reference
						}
						'sign inversion' { [ - ] }
					)
					'expression': component 'scalar expression'
				}
				'list expression' {
					'operation': stategroup (
						'sum' { [ sum ] }
						'minimum' { [ min ] }
						'maximum' { [ max ] }
						'product' { [ product ] }
					)
					'expression': [ (, ) ] component 'scalar expression list'
				}
				'binary expression' {
					'operation': stategroup (
						'division' { [ division ]
							'rounding': stategroup (
								'ordinary' { }
								'ceil' { [ ceil ] }
								'floor' { [ floor ] }
							)
						}
						'remainder' { [ remainder ] }
					)
					'expressions': group { [ (, ) ]
						'left': component 'scalar expression'
						'right': [ , ] component 'scalar expression'
					}
				}
			)
		}
		'text' {
			'type': stategroup (
				'static' {
					'value': text
				}
			)
		}
		'dynamic' {
			'path': component 'singular node path'
			'property': [ . ] reference
		}
	)
}

Metadata

The metadata recording enables you to record the mutation times of scalar values in your application: texts, numbers, and files.

'metadata recording' {
	'record mutation time': stategroup (
		'yes' { [ mutation-time ]
			'meta property': [ = . ] reference
		}
		'no' { }
	)
}

Navigation steps:

.'My Property'          // get property value
?'My State'             // require state
>'My Text'              // get referenced node (for text properties with a reference)
.'My Text'&'Where'      // get 'where'-rule value from property
.&'My State Where'      // get 'where'-rule result from context state
.'My Collection'*       // iterate collection
--
^              // go to parent node
$^             // go to parent context with $ object
$              // select nearest $ object
@              // select nearest parameter node

'ancestor node path' {
	'has steps': stategroup (
		'no' { }
		'yes' { [ ^ ]
			'tail': component 'ancestor node path'
		}
	)
}

'context node path' {
	'context': stategroup (
		'dynamic user' { [ user ] }
		'this' { }
		'variable' {
			'name': stategroup (
				'implicit' { [ $ ] }
				'explicit' {
					'head': component 'ancestor variable path'
					'variable': [ $ ] reference
				}
			)
		}
		'parameter' { [ @ ] }
	)
}

'node step' {
	'type': stategroup (
		'parent' { [ ^ ] }
		'property rule' {
			'text': [ . ] reference
			'rule': [ & ] reference
		}
		'group' { [ . ]
			'group': reference
		}
		'state context rule' {
			'rule': [ .& ] reference
		}
		'state' {
			'state group': [ . ] reference
			'state': [ ? ] reference
		}
		'reference' { [ > ]
			'text': reference
		}
	)
}

'node path tail' {
	'has steps': stategroup (
		'no' { }
		'yes' {
			'step': component 'node step'
			'tail': component 'node path tail'
		}
	)
}

'node path' {
	'head': component 'context node path'
	'tail': component 'node path tail'
}

'singular node path' {
	'path': component 'node path'
}

'conditional node path' {
	'path': component 'node path'
}

'descendant node path' {
	'has steps': stategroup (
		'no' { }
		'yes' {
			'property': [ . ] reference
			'value type': stategroup (
				'choice' {
					'state': [ ? ] reference
				}
				'node' { }
			)
			'tail': component 'descendant node path'
		}
	)
}

'descendant property path' {
	'head': component 'descendant node path'
	'property': [ . ] reference
}

'node expression' {
	'node path': component 'conditional node path'
	'type': stategroup (
		'equality' {
			'expected node path': [ is (, ) ] component 'conditional node path'
		}
		'existence' { }
		'containment' {
			'collection': [ . ] reference
			'key path': [ [, ] ] group {
				'path': component 'conditional node path'
				'text': [ . ] reference
			}
		}
	)
}

'optional variable assignment' {
	'has assignment': stategroup (
		'no' { }
		'yes' { [ as ]
			'assignment': component 'variable assignment'
		}
	)
}

'variable assignment' {
	'name': stategroup (
		'implicit' { [ $ ] }
		'explicit' {
			'name': reference = first
			'named objects': dictionary { [ $ ]
				'has successor': stategroup = node-switch successor (
					| node = 'yes' { }
					| none = 'no'
				)
			}
		}
	)
}

'named object assignment' {
	'name': stategroup (
		'implicit' { [ $ ] }
		'explicit' {
			'name': reference = first
			'named objects': dictionary { [ $ ]
				'has successor': stategroup = node-switch successor (
					| node = 'yes' { }
					| none = 'no'
				)
			}
		}
	)
}

'optional named object assignment' {
	'has assignment': stategroup (
		'no' { }
		'yes' { [ as ]
			'assignment': component 'named object assignment'
		}
	)
}

'ancestor named object path' {
	'has steps': stategroup (
		'no' { }
		'yes' { [ $^ ]
			'tail': component 'ancestor named object path'
		}
	)
}

'ancestor variable path' {
	'has steps': stategroup (
		'no' { }
		'yes' { [ $^ ]
			'tail': component 'ancestor variable path'
		}
	)
}

'singular variablized object path' {
	'path': component 'variablized object path'
}

'context object step' {
	'context': stategroup (
		'this' { }
		'parameter' { [ @ ] }
		'variable' {
			'name': stategroup (
				'implicit' { [ $ ] }
				'explicit' {
					'head': component 'ancestor named object path'
					'named object': [ $ ] reference
				}
			)
		}
	)
}

'variablized object path' {
	'head': component 'context object step'
	'path': component 'object path tail'
}

'group ancestor path' {
	'has steps': stategroup (
		'no' { }
		'yes' { [ ^ ]
			'tail': component 'group ancestor path'
		}
	)
}

'ancestor attribute path' {
	'has steps': stategroup (
		'no' { }
		'yes' { [ ^ ]
			'tail': component 'ancestor attribute path'
		}
	)
}

'property step' {
	'property': [ . ] reference
}

'dependency step' {
	'type': stategroup (
		'reference' {
			'reference': [ > ] reference
		}
		'reference rule' {
			'property': component 'property step'
			'rule': [ & ] reference
		}
		'state context rule' {
			'rule': [ .& ] reference
		}
	)
}

'object path tail' {
	'has steps': stategroup (
		'no' { }
		'yes' {
			'type': stategroup (
				'parent' { [ ^ ] }
				'property value' {
					'property': component 'property step'
				}
				'dependency' {
					'dependency': component 'dependency step'
				}
				'reference set' {
					'reference set': [ < ] reference
				}
				'state' {
					'state': [ ? ] reference
				}
			)
			'tail': component 'object path tail'
		}
	)
}

'descendant object path' {
	'path': component 'object path tail'
}

'object set path' {
	'collection path': component 'singular variablized object path'
	'value path': [ * ] component 'object path tail'
}

'entry reference selector' {
	'definer': stategroup (
		'property' {
			'property': [ > ] reference
		}
		'rule' {
			'property': [ . ] reference
			'rule': [ & ] reference
		}
	)
}

User interface annotations

User interface annotations, or annotations for short, are recognizable by the @ character before the keyword. E.g. @default:. Most annotations affect generated user interfaces (a system of type auto-webclient); they typically do not affect custom user interfaces (system type webclient).

It is possible to use multiple annotations on a single property. Be aware that they should be added in a specific order. Consult this grammar for the order of annotations.

Overview

Different attribute types support the same types of annotations. This overview presents the commonly used annotations that different attribute types share.

Defaults

Most property types support the @default: annotation. Defaults apply default values to properties of new nodes only and fail silently. That is, if the path contains a state navigation step and the stategroup is not in that state, the default won’t be applied. In the following example the Score property will not be set when the state of Default Score is anything other than Known.

'Score': number positive 'score' @default: .'Default Score'?'Known'.'Value'

A default value is not necessarily a valid value. If validation rules or constraints apply, a default value can be invalid. When a derived value is used, make sure it is not a part of the new node. Derived values on new nodes are computed after the node is saved, and will therefore not be included in default values. For example, this initializes the Description with Deliver pieces:

'Description': text @default: concat ( "Deliver ", to-text .'To deliver', " pieces." )
'To deliver' : number 'pieces' = ^ >'Order'.'Amount'

Descriptions

All attribute types support the @description: annotation. This annotation adds additional information about an attribute: what it is meant for. Alan GUI’s typically present it as alt text, or a compact description at an input field.

Visibility

Commands and attributes that hold derived values, support the @hidden annotation. The annotation hides an attribute from the UI.

Identifying properties

Properties that are important for the identification of a collection entry can be marked with the @identifying annotation. Identifying properties are shown together with the unique identifier of a collection entry, whenever the entry is referenced. For example, when an employee has a uniquely identifying personnel number in a collection of employees, a reference to employee will show the name of the employee when the ‘name’ property is marked as identifying.

'ui identifying property selection' {
	'has properties': stategroup = node-switch .'properties' (
		| nodes = 'yes' { 'first' = first }
		| none  = 'no'
	)
	'properties': [ (, ) ] dictionary {
		'has successor': stategroup = node-switch successor (
			| node = 'yes' { 'successor' = successor }
			| none = 'no'
		)
		'type': [ : ] stategroup (
			'text' { [ text ] }
			'number' { [ number ] }
			'group' { [ group ]
				'selection': component 'ui identifying property selection'
			}
			'state group' { [ stategroup ]
				'has identifying states': stategroup (
					'no' { }
					'yes' {
						'identifying': stategroup (
							'no' { [ hide ] }
							'yes' { }
						)
						'first state': reference = first
						'states': [ (, ) ] dictionary {
							'has successor': stategroup = node-switch successor (
								| node = 'yes' { 'successor' = successor }
								| none = 'no'
							)
							'selection': component 'ui identifying property selection'
						}
					}
				)
			}
		)
	}
}

Icons

For better visual identification, attributes support the @icon: annotation attribute. As an argument it takes an icon name. A complete list of the supported icons can be found at: fonts.google.com/icons.

Actions

An action attribute describes a sequence of actions (operations), as explained in the section on action attributes.

'ui action' { [ => ]
	'expression': component 'ui expression'
	'has next action': stategroup (
		'yes' {
			'action': component 'ui action'
		}
		'no' { }
	)
}

The keyword interactive instructs your application to display a screen to the user for applying/executing an operation.

'ui action interaction' {
	'interactive': stategroup (
		'yes' { [ interactive ] }
		'no' { }
	)
}

The keyword show presents the result of an operation after performing it.

'ui action visualization' {
	'show target': stategroup (
		'yes' { [ show ] }
		'no' { }
	)
}

'ui object expression' {
	'properties': [ (, ) ] dictionary {
		'default': [ = ] component 'ui expression'
	}
}

'ui entry expression list' {
	'entry expression': component 'ui expression'
	'more entries': stategroup (
		'no' { }
		'yes' { [ , ]
			'tail': component 'ui entry expression list'
		}
	)
}

'ui expression' {
	'operation': stategroup (
		'state switch' { [ switch ]
			'path': group {
				'path': component 'ui parametrized node path'
				'stategroup': [ . ] reference
			}
			'states': [ (, ) ] dictionary { [ | ]
				'variable assignment': component 'optional variable assignment'
				'expression': [ => ] component 'ui expression'
			}
		}
		'node switch' { [ switch ]
			'expression': component 'node expression'
			'cases': [ (, ) ] group {
				'node case': [ | node ] group {
					'variable assignment': component 'optional variable assignment'
					'expression': [ => ] component 'ui expression'
				}
				'none case': [ | none ] group {
					'expression': [ => ] component 'ui expression'
				}
			}
		}
		'walk' { [ walk ]
			'path': component 'singular node path'
			'collection': [ . ] reference
			'variable assignment': component 'optional variable assignment'
			'expression': [ (, ) ] component 'ui expression'
		}
		'ignore' { [ ignore ] }
		'update properties' { [ update ]
			'path': component 'singular node path'
			'target': stategroup (
				'node' {
					'interaction': component 'ui action interaction'
					'visualization': component 'ui action visualization'
					'expression': component 'ui object expression'
				}
				'collection' {
					'collection': [ . ] reference
					'expression': [ = ] component 'ui expression'
				}
			)
		}
		'execute operation' { [ execute ]
			'interaction': component 'ui action interaction'
			'path': component 'singular node path'
			'operation': [ . ] reference
			'expression': component 'ui object expression'
		}
		'produce value' {
			'value': stategroup (
				'object' {
					'expression': component 'ui object expression'
				}
				'state' {
					'state': [ create ] reference
					'expression': component 'ui object expression'
				}
				'scalar' {
					'expression': component 'ui scalar value expression'
				}
			)
		}
		'entry list' { [ (, ) ]
			'entries': component 'ui entry expression list'
		}
		'entry' {
			'type': stategroup (
				'create' { [ create ]
					'interaction': component 'ui action interaction'
					'visualization': component 'ui action visualization'
					'expression': component 'ui object expression'
				}
				'delete' { [ delete ]
					'interaction': component 'ui action interaction'
					'path': component 'singular node path'
				}
			)
		}
	)
}

'ui scalar value expression list' {
	'value': component 'ui scalar value expression'
	'has tail': stategroup (
		'no' { }
		'yes' { [ , ]
			'tail': component 'ui scalar value expression list'
		}
	)
}

'ui scalar value expression' {
	'type': stategroup (
		'text' {
			'type': stategroup (
				'auto increment' { [ auto-increment ]
					'scope': component 'ancestor node path'
				}
				'static' {
					'value': text
				}
				'current user' { [ user ] }
				'guid' { [ guid ] }
				'number to text' { [ to-text ]
					'numerical type': reference
					'pad': stategroup (
						'yes' { [ pad ]
							'size': integer
							'character': [ with ] text
						}
						'no' { }
					)
					'expression': component 'ui scalar value expression'
				}
				'concatenation' { [ concat (, ) ]
					'list': component 'ui scalar value expression list'
				}
			)
		}
		'number' {
			'type': stategroup (
				'constant' {
					'value': component 'constant number value'
				}
				'now in seconds' { [ now ] }
				'unary expression' {
					'type': stategroup (
						'absolute value' { [ abs ] }
						'numerical type conversion' { [ from ]
							'representation based': stategroup (
								'ui date and time' { [ @date-time ] }
								'no' { }
							)
							'conversion': reference
						}
						'sign inversion' { [ - ] }
					)
					'expression': component 'ui scalar value expression'
				}
				'list expression' {
					'operation': stategroup (
						'sum' { [ sum ] }
						'minimum' { [ min ] }
						'maximum' { [ max ] }
						'product' { [ product ] }
					)
					'value': [ (, ) ] component 'ui scalar value expression list'
				}
				'binary expression' {
					'operation': stategroup (
						'division' { [ division ]
							'rounding': stategroup (
								'ordinary' { }
								'ceil' { [ ceil ] }
								'floor' { [ floor ] }
							)
						}
						'remainder' { [ remainder ] }
					)
					'expressions': group { [ (, ) ]
						'left': component 'ui scalar value expression'
						'right': [ , ] component 'ui scalar value expression'
					}
				}
			)
		}
		'style' {
			'type': stategroup (
				'property' { [ to-color ]
					'expression': component 'ui scalar value expression'
				}
				'fixed' {
					'style': component 'ui style'
				}
			)
		}
		'state' {
			'state': reference
		}
		'dynamic' {
			'path': component 'ui parametrized node path'
			'property': [ . ] reference
		}
		'sticky' { [ sticky ] }
	)
}

'ui scalar default' {
	'expression': component 'ui expression'
	'has fallback': stategroup (
		'yes' { [ || ]
			'fallback': component 'ui scalar default'
		}
		'no' { }
	)
}

'ui style' {
	'style': stategroup (
		'foreground' { [ foreground ] }
		'background' { [ background ] }
		'brand' { [ brand ] }
		'link' { [ link ] }
		'accent' { [ accent ] }
		'success' { [ success ] }
		'warning' { [ warning ] }
		'error' { [ error ] }
	)
}

'ui text validation' {
	'regular expression': text
}

'ui parametrized node path' {
	'path': component 'conditional node path'
}

'ui node path' {
	'path': component 'node path'
}

'ui node path tail' {
	'path': component 'node path tail'
}

'node type id' {
	'steps': component 'node type id path'
}

'node type id path' {
	'has steps': stategroup (
		'no' { }
		'yes' {
			'property': [ . ] reference
			'value type': stategroup (
				'choice' {
					'state': [ ? ] reference
				}
				'node' { }
				'collection' { [ * ] }
			)
			'tail': component 'node type id path'
		}
	)
}

Commands

'ui command attribute' {
	'visible': stategroup (
		'true' { }
		'false' { [ @hidden ] }
	)
}

Groups

The @breakout annotation indicates that a group property should not be displayed together with the other properties. At the time of this writing, the group is put in a separate tab in the details view of an entry. Note that the tab is always added to the top level tabs of a details view. That is, if a group is inside a state or another group, it is not added to the tabs of the state.

'ui group property' { dynamic-order
	'visible': stategroup (
		'true' {
			'break out': stategroup (
				'no' { }
				'yes' { [ @breakout ] }
			)
		}
		'false' { [ @hidden ] }
	)
	'has description': stategroup (
		'no' { }
		'yes' { [ @description: ]
			'description': text
		}
	)
	'icon': stategroup (
		'no' { }
		'yes' { [ @icon: ]
			'name': text
		}
	)
}

Collections

The @default: annotation copies entries of a source collection into the annotated collection. A subset of the entries from the source collection can be copied by specifying a state filter:

'Labels': collection ['Name'] {
	'Name': text
	'Default': stategroup (
		'Yes' { }
		'No' { }
	)
}
'Issues': collection ['Name']  {
	'Name': text
	'Labels': collection ['Name'] @default: >'Name'.'Default'?'Yes' {
		'Name': text -> ^ ^ .'Labels'[]
	}
}

This only applies to new nodes holding collections. This annotation does nothing for collections on the root node:

root {
	'People': collection ['Name'] {
		'Name': text
	}
	'Employees': collection ['Name'] @default: >'Name' { // This has no effect.
		'Name': text
	}
}

Collections can only be initialized from the collection that it references, using the key property, or using a derived link that derives from the key. In the latter case, other collections can be used to initialize an entry as long as the keys are the same.

'Imported Categories': collection ['Id'] {
	'Id': text
}
'Gegevens': collection ['Id'] @default: >'Category' {
	'Id': text /* -> some constraint or not */
	'Category': text ~> ^ .'Imported Categories'[] = .'Id'
}

'ui collection property' { dynamic-order
	'sort': stategroup (
		'no' { }
		'yes' {
			'direction': stategroup (
				'ascending' { [ @ascending: ] }
				'descending' { [ @descending: ] }
			)
			'path': component 'ui node path'
			'property': [ . ] reference
		}
	)
	'visible': stategroup (
		'true' {
			'break out': stategroup (
				'no' { }
				'yes' { [ @breakout ] }
			)
		}
		'false' { [ @hidden ] }
	)
	'size': stategroup (
		'small' { [ @small ] }
		'large' { }
	)
	'can be dormant': stategroup (
		'no' { }
		'yes' { [ @dormant: ]
			'state group path': component 'descendant property path'
			'dormant state': [ ? ] reference
		}
	)
	'has description': stategroup (
		'no' { }
		'yes' { [ @description: ]
			'description': text
		}
	)
	'default': stategroup (
		'no' { }
		'yes' { [ @default: ]
			'key reference': component 'entry reference selector'
			'entry filter': component 'ui node path tail'
		}
	)
	'icon': stategroup (
		'no' { }
		'yes' { [ @icon: ]
			'name': text
		}
	)
	'has style': stategroup (
		'no' { }
		'yes' { [ @style: ]
			'style expression': component 'ui expression'
		}
	)
}

Numbers

'ui number property' { dynamic-order
	'visible': stategroup (
		'true' { }
		'false' { [ @hidden ] }
	)
	'identifying': stategroup (
		'no' { }
		'yes' { [ @identifying ] }
	)
	'emphasis': stategroup (
		'no' { }
		'yes' { [ @emphasis ] }
	)
	'default': stategroup (
		'no' { }
		'yes' { [ @default: ]
			'default': component 'ui scalar default'
		}
	)
	'dynamic numerical type': stategroup (
		'no' { }
		'yes' { [ @numerical-type: ]
			'binding path': component 'node path'
		}
	)
	'metadata': stategroup (
		'no' { }
		'yes' { [ @metadata ] }
	)
	'validation': group {
		'has minimum': stategroup (
			'no' { }
			'yes' { [ @min: ]
				'minimum': component 'ui scalar value expression'
			}
		)
		'has maximum': stategroup (
			'no' { }
			'yes' { [ @max: ]
				'maximum': component 'ui scalar value expression'
			}
		)
	}
	'has description': stategroup (
		'no' { }
		'yes' { [ @description: ]
			'description': text
		}
	)
	'icon': stategroup (
		'no' { }
		'yes' { [ @icon: ]
			'name': text
		}
	)
}

Files

'ui file property' { dynamic-order
	'file name expression': stategroup (
		'no' { }
		'yes' { [ @name: ]
			'file name expression': component 'ui scalar default'
		}
	)
	'visible': stategroup (
		'true' { }
		'false' { [ @hidden ] }
	)
	'has description': stategroup (
		'no' { }
		'yes' { [ @description: ]
			'description': text
		}
	)
	'icon': stategroup (
		'no' { }
		'yes' { [ @icon: ]
			'name': text
		}
	)
	'identifying': stategroup (
		'no' { }
		'yes' { [ @identifying ] }
	)
}

Texts

'ui text property' { dynamic-order
	'visible': stategroup (
		'true' { }
		'false' { [ @hidden ] }
	)
	'identifying': stategroup (
		'no' { }
		'yes' { [ @identifying ] }
	)
	'emphasis': stategroup (
		'no' { }
		'yes' { [ @emphasis ] }
	)
	'type': stategroup (
		'default' { }
		'multi-line' { [ @multi-line ] }
		'color' { [ @color ] }
	)
	'default value': stategroup (
		'no' { }
		'yes' { [ @default: ]
			'default': component 'ui scalar default'
		}
	)
	'has validation': stategroup (
		'no' { }
		'yes' { [ @validate: ]
			'type': stategroup (
				'regular expression' {
					'rules': component 'ui text validation'
				}
				'optional reference must resolve' { [ resolvable ] }
			)
		}
	)
	'has description': stategroup (
		'no' { }
		'yes' { [ @description: ]
			'description': text
		}
	)
	'icon': stategroup (
		'no' { }
		'yes' { [ @icon: ]
			'name': text
		}
	)
	'has custom identifying properties': stategroup (
		'no' { }
		'yes' { [ @show: ]
			'selection': component 'ui identifying property selection'
		}
	)
	'is label': stategroup (
		'no' { }
		'yes' { [ @label ] }
	)
}

State groups

'ui state group property' { dynamic-order
	'visible': stategroup (
		'true' { }
		'false' { [ @hidden ] }
	)
	'identifying': stategroup (
		'no' { }
		'yes' { [ @identifying ] }
	)
	'emphasis': stategroup (
		'no' { }
		'yes' { [ @emphasis ] }
	)
	'default state': stategroup (
		'no' { }
		'yes' { [ @default: ]
			'default': component 'ui scalar default'
		}
	)
	'has description': stategroup (
		'no' { }
		'yes' { [ @description: ]
			'description': text
		}
	)
	'icon': stategroup (
		'no' { }
		'yes' { [ @icon: ]
			'name': text
		}
	)
}

States

'ui state' { dynamic-order
	'desired state': stategroup (
		'no' { }
		'yes' { [ @desired ] }
	)
	'verified state': stategroup (
		'no' { }
		'yes' { [ @verified ] }
	)
	'icon': stategroup (
		'no' { }
		'yes' { [ @icon: ]
			'name': text
		}
	)
	'has style': stategroup (
		'no' { }
		'yes' { [ @style: ]
			'style expression': component 'ui expression'
		}
	)
	'transitions': dictionary { [ @transition: ]
		'action': [ => execute ] reference
	}
}

Todo items

'ui todo' {
	'has description': stategroup (
		'no' { }
		'yes' { [ @description: ]
			'description': text
		}
	)
}

Numerical types

'ui numerical type' {
	'represent as': stategroup (
		'model' { }
		'date' { [ @date ] }
		'date and time' { [ @date-time ] }
		'duration' { [ @duration: ]
			'unit': stategroup (
				'seconds' { [ seconds ] }
				'minutes' { [ minutes ] }
				'hours' { [ hours ] }
			)
		}
		'custom type' { [ @numerical-type: ]
			'binding': stategroup (
				'root' { }
				'dynamic' { [ bind ]
					'path': component 'node type id'
					'assignment': [ as ] component 'variable assignment'
				}
			)
			'properties': [ (, ) ] group {
				'label': [ label: ] component 'ui scalar value expression'
				'conversion': stategroup (
					'none' { }
					'point translation' {
						'decimals': [ decimals: ] component 'ui scalar value expression'
					}
				)
			}
		}
	)
}

application

The minimal model

Data model structure

The root rule

Application users

Interfaces

The root node type

Numerical types

Node types

Property attributes

Reference set attributes

Command attributes

Action attributes

References

Reference behaviour

Upstream & downstream

Bidirectional references

Sibling references

Graph constraints

Derived values

Upstream, downstream, and sibling dependence

Expressions

Derived texts

Derived numbers

Derived files

Derived states

Derived references

Derived collections

Permissions and Todos

Permissions

Read permissions

Update permissions

Create and delete permissions

Command execution permissions

Todo items

User requirements

Commands and Timers

Metadata

Navigation

Node navigation

Variable assignment and navigation

Navigation for constraints & derivations

User interface annotations

Overview

Defaults

Descriptions

Visibility

Identifying properties

Icons

Actions

Commands

Groups

Collections

Numbers

Files

Texts

State groups

States

Todo items

Numerical types

The `root` rule

The `root` node type