Associations and Association Links (CDM)

In the Merise modeling methodology an association is used to connect several entities that each represents clearly defined objects, but are linked by an event, which may not be so clearly represented by another entity.

Each instance of an association corresponds to an instance of each entity linked to the association.

When you generate a PDM from a CDM, associations are generated as tables or references.

In the following example, three entities VIDEOK7, CLIENT, and STORE contain video cassette, client, and store information. They are linked by an association which represents a video cassette rental (K7RENTAL). The K7RENTAL association also contains the attributes DATE and STAFF_ID, which give the date of the rental, and the identity of the staff member who rented out the video cassette.

When you generate a PDM, K7RENTED is generated as a table with five columns, STORE_ID,K7_ID, CLIENT_ID, DATE, and STAFF_ID.

You can use associations exclusively in your CDM, or use both associations and relationships.

• Creating an Association with Links
  The easiest way to create an association between entities is to use the Association Link tool, which will create the association and the necessary links as well.
• Creating an Association Without Links
  You can create an association without links from the Toolbox, Browser, or Model menu.
• Association Properties
  To view or edit an association's properties, double-click its diagram symbol or Browser or list entry. The property sheet tabs and fields listed here are those available by default, before any customization of the interface by you or an administrator.
• Association Link Properties
  To view or edit an association link's properties, double-click its diagram symbol or Browser or list entry. The property sheet tabs and fields listed here are those available by default, before any customization of the interface by you or an administrator.
• Creating a Reflexive Association
  A reflexive association is a relationship between an entity and itself.
• Defining a Dependent Association
  In a dependent association, one entity is partially identified by another. Each entity must have an identifier. In some cases, however, the attributes of an entity are not sufficient to identify an occurrence of the entity. For these entities, their identifiers incorporate the identifier of another entity with which they have a dependent association.
• Changing an Association into an Associative Entity
  You can transform an association into an associative entity linked by two associations. The associative entity gets the name and code of the association. The two new associations handle cardinality properties.
• Creating an Association Attribute
  The tools used for creating association attributes on this tab are the same as those for creating entity attributes.