HP 3000 Manuals HP 3000 Manuals
Type-Attribute Associations You can assign an attribute of type Boolean, character, floating, or integer to any entity type or relationship type. This is referred to as creating a type-attribute association. When an attribute is associated with an entity type or relationship type, all entities or relationships of that type must have a value for that attribute. Type-attribute associations build the attribute lists of entity types and relationship types. System Dictionary has a built-in set of type-attribute associations. These type-attribute associations are part of the core set and cannot be deleted. You can extend the dictionary by creating other type-attribute associations. You can add attributes to core set entity types and relationship types or to new entity types and relationship types. You can later remove these associations from the extended set. Entity-Type-Attribute Associations Entity types are templates for defining the set of attribute values in each entity of that type. When you create a type-attribute association, the template is changed and a corresponding change must be made in the attribute values of each entity of that type. The change, which involves assigning the attribute's default value to each entity, happens during restructuring when the dictionary is closed. (Restructuring of the dictionary is discussed later in this chapter.) Similarly, when you delete an entity-type-attribute association, System Dictionary must remove the corresponding attribute value from each entity of the affected type. Relationship-Type-Attribute Associations Relationship types are templates for defining the attribute values of relationships. When you create or delete a relationship-type-attribute association, the template is changed, and a corresponding change must be made in each relationship of the affected type.