Binary Relation

A relation between two members. It may connect two classes, or — for derivation relations — a relation (as source) and a class (as target), as in the derivation between the material relation studies in and the Enrollment relator.

Property	Type	Description
`type`	`"BinaryRelation"`	Discriminator.

BinaryRelation carries the properties of Classifier (isAbstract, properties), Decoratable (stereotype, isDerived), and the properties common to all model elements. A binary relation's two ends are Property elements referenced, in order, from its properties array (inherited from Classifier).

The example below is the «material» studies in relation connecting the classes Student and University. Its two ends — the Property elements listed in properties — are drawn with their cardinalities (1..* at each end).

{
  "type": "BinaryRelation",
  "id": "relation_1",
  "name": { "en": "studies in" },
  "stereotype": "material",
  "isDerived": false,
  "isAbstract": false,
  "properties": ["end_source", "end_target"],
  "customProperties": null,
  "created": "2024-09-04",
  "modified": null,
  "alternativeNames": [],
  "description": null,
  "editorialNotes": [],
  "creators": [],
  "contributors": []
}

The ends themselves are separate Property objects, listed elsewhere in the document and referenced by id from properties. Each end carries the cardinality drawn on the diagram and points, via propertyType, to the class it connects — end_source to Student and end_target to University.

{
  "type": "Property",
  "id": "end_source",
  "name": null,
  "stereotype": null,
  "isDerived": false,
  "propertyType": "class_student",
  "cardinality": "1..*",
  "aggregationKind": null,
  "isOrdered": false,
  "isReadOnly": false,
  "subsettedProperties": [],
  "redefinedProperties": [],
  "customProperties": null,
  "created": "2024-09-04",
  "modified": null,
  "alternativeNames": [],
  "description": null,
  "editorialNotes": [],
  "creators": [],
  "contributors": []
}

{
  "type": "Property",
  "id": "end_target",
  "name": null,
  "stereotype": null,
  "isDerived": false,
  "propertyType": "class_university",
  "cardinality": "1..*",
  "aggregationKind": null,
  "isOrdered": false,
  "isReadOnly": false,
  "subsettedProperties": [],
  "redefinedProperties": [],
  "customProperties": null,
  "created": "2024-09-04",
  "modified": null,
  "alternativeNames": [],
  "description": null,
  "editorialNotes": [],
  "creators": [],
  "contributors": []
}

Parthood and aggregation

Parthood relations record which end is the whole through the aggregationKind of that end. The example below is a «componentOf» relation between the whole Car and its part Engine. In UML it is drawn with a filled diamond at the whole end.

{
  "type": "BinaryRelation",
  "id": "relation_3",
  "name": null,
  "stereotype": "componentOf",
  "isDerived": false,
  "isAbstract": false,
  "properties": ["end_car", "end_engine"],
  "customProperties": null,
  "created": "2024-09-04",
  "modified": null,
  "alternativeNames": [],
  "description": null,
  "editorialNotes": [],
  "creators": [],
  "contributors": []
}

The whole end (end_car) sets aggregationKind to "COMPOSITE" — the filled diamond. The part end (end_engine) illustrates two further flags: isOrdered (the order of a car's engines is meaningful) and isReadOnly (an engine cannot be reassigned to another car once linked).

{
  "type": "Property",
  "id": "end_car",
  "name": null,
  "stereotype": null,
  "isDerived": false,
  "propertyType": "class_car",
  "cardinality": "1",
  "aggregationKind": "COMPOSITE",
  "isOrdered": false,
  "isReadOnly": false,
  "subsettedProperties": [],
  "redefinedProperties": [],
  "customProperties": null,
  "created": "2024-09-04",
  "modified": null,
  "alternativeNames": [],
  "description": null,
  "editorialNotes": [],
  "creators": [],
  "contributors": []
}

{
  "type": "Property",
  "id": "end_engine",
  "name": null,
  "stereotype": null,
  "isDerived": false,
  "propertyType": "class_engine",
  "cardinality": "1..*",
  "aggregationKind": "NONE",
  "isOrdered": true,
  "isReadOnly": true,
  "subsettedProperties": [],
  "redefinedProperties": [],
  "customProperties": null,
  "created": "2024-09-04",
  "modified": null,
  "alternativeNames": [],
  "description": null,
  "editorialNotes": [],
  "creators": [],
  "contributors": []
}

Parthood and aggregation​

Parthood and aggregation