Choosing Physical Tuning Options › Relationship Tuning Options › Membership Options

Membership Options

Membership options determine how an entity is connected to and disconnected from a relationship. These options affect the use of the DML STORE, CONNECT, DISCONNECT, and ERASE statements.

You define membership options in two parts. The first part indicates the manner (mandatory or optional) in which the entity is disconnected from a linked relationship. The second part indicates the manner (automatic or manual) in which the entity is connected to a linked relationship.

Disconnect options

The disconnect options operate as follows:

• Mandatory— A child occurrence cannot be disconnected from the relationship without also being erased from the database (that is, the DML DISCONNECT verb cannot be issued against entities in the relationship).
• Optional— A child occurrence can be disconnected from a relationship by the DISCONNECT verb. The entity occurrence remains in the database and is accessible in other ways; it can be connected to another relationship.

The mandatory/optional membership specification affects the outcome of the DML ERASE statement. If any of the ERASE options (PERMANENT, SELECTIVE, ALL) is specified when an ERASE statement is issued against an entity, all mandatory entities owned by that entity are also erased. Optional child entity occurrences are left as is, disconnected, or erased, depending on the ERASE option specified.

Mandatory disconnect

The disconnect option is usually specified as mandatory. However, do not specify the mandatory disconnect option when:

• An application requires the ability to dissociate a child entity occurrence from its parent (usually with the intention of associating the child with another parent occurrence). At Commonweather Corporation, employees sometimes need to be transferred from one department to another. Therefore, the disconnect option for the DEPT-EMPLOYEE relationship must be specified as optional

  Important! Be careful when using the optional disconnect option for child entities of a relationship stored clustered around that relationship. If the entity is later disconnected from its original parent and connected to another, CA IDMS/DB does not physically relocate the entity; for all practical purposes, that entity is no longer clustered around its parent.

• An application requires the ability to erase a parent entity without erasing the child entities (using the ERASE PERMANENT and ERASE SELECTIVE functions). Suppose the Commonweather Corporation decides to close an office in a certain city. In this case, the office should be erased, but the employees who work in that office should not be erased.

Connect options

The connect options operate as follows:

• Automatic—The membership of an entity in a relationship is established automatically by the DBMS whenever a child occurrence is stored in the database.
• Manual—The membership of an entity in a relationship is not established when a child occurrence is stored. Membership must be established explicitly by using the DML CONNECT statement.

Disconnect and connect options are combined to form membership options:

• MA— Mandatory automatic
• MM— Mandatory manual
• OA— Optional automatic
• OM— Optional manual

Automatic connect

The connect option is usually specified as automatic. However, do not specify the automatic connect option when:

• An application requires the ability to store a child entity without associating it with any parent. For example, at Commonweather Corporation, an employee can join the company without first being assigned to a department. Therefore, the manual option must be specified for the DEPT-EMPLOYEE relationship.
• If two relationships exist between the same two entities representing a self-referencing relationship, only one of the relationships can be automatic; the other must be manual. Otherwise, a child would be connected to the same parent occurrence in each relationship, as shown below.

  

  

Guidelines

The manual connect and optional disconnect options permit greater flexibility but require more programming effort. Additionally, they provide less control over data integrity. You should therefore choose the mandatory automatic (MA) membership option, unless there exists a special business requirement for optional disconnect and/or manual connect functions.

Representing membership options

Represent membership options for a relationship on the data structure diagram by specifying the membership options to be used: MA, MM, OA, or OM.