Relationship
A relationship represents a logical link between an independent entity (the parent) and a dependent entity (the child), and is labeled with a verb phrase that describes the link between the parent and the child. A relationship has an associated cardinality, which specifies the number of instances of the child that are related to an instance of the parent.
Properties
Relationships in AWM are defined with the following properties:- Name (mandatory)
- A textual name that identifies this relationship. The name is based on the
parent entity name, the child entity name, or both.
- e.g. relationship Meter Reading Detail_Meter Reading_FK
- Relationship type (mandatory)
- Identifying
- The foreign key is part of the child entity primary key, for example. Its attributes help to uniquely identify a child record.
- Non-Identifying
- The foreign key is not part of the child entity primary key.
- e.g. anchor entity Meter Reading has an identifying relationship with child associative entity Meter Reading Detail
- Existence (mandatory)
- Mandatory
- The relationship must exist between either the parent or the child entities perspective.
- Optional
- The relationship may exist from either the parent or the child entities perspective.
- Cardinality (mandatory)
- The number of children that the parent can have in this relationship.
This can be one of the following values:
- Zero or more
- One or more
- Zero or one
- Exactly one
- e.g. parent entity Meter Reading has one or more children entities Meter Reading Detail in relationship Meter Reading Detail_Meter Reading_FK
- Parent entity (mandatory)
- The entity that represents the independent entity in this relationship.
- e.g. anchor entity Meter Reading / Usage Point is parent of relationship Meter Reading / System Resource_Meter Reading_FK
- Parent verb phrase (mandatory)
- The verb phrase in lower case, describing how the parent entity
is related to the child entity of this relationship.
- e.g. parent entity System Resource is related to child entity Measurement / System Resource with verb is parent of
- Child entity (mandatory)
- The entity that represents the dependent entity in this relationship.
- e.g. associative entity Measurement / System Resource is child of Measurement
- Child inverse verb phrase (mandatory)
- The verb phrase in lower case, describing how the child entity
is related to the parent entity of this relationship.
- e.g. child entity Measurement / System Resource is related to parent entity System Resource with verb has for parent