Choosing Physical Tuning Options › Relationship Tuning Options › Linkage

Linkage

Each entity in the database carries one, two, or three pointers for each chained relationship in which it participates. You should usually include all allowable pointers for each entity:

• Next pointer—Required for all relationships in which the entity participates as parent or child; the next pointer is the database key of the next entity in the relationship. The last child entity in a relationship points to the parent.
• Prior pointer—Optional for all relationships in which the entity participates as parent or child; the prior pointer is the database key of the prior entity in the relationship. The first child entity occurrence in a relationship points to the parent.
• Owner pointer—Optional for all relationships in which the entity participates as a child; the parent pointer is the database key of the parent entity occurrence.

Omitting prior pointers

Prior pointers can be omitted under the following conditions:

• Child entity occurrences in the relationship will not be erased or disconnected except by walking the set.
• Child entity participates as a child in no other relationship.
• Order is not LAST or PRIOR (see "Nonsorted Order" above).
• The FIND/OBTAIN LAST or FIND/OBTAIN PRIOR DML functions will not be used for the relationship.

Omitting owner pointers

Owner pointers (db-keys pointing to the parent) can be omitted under the following conditions:

• The parent will not be accessed from a child occurrence.
• The FIND/OBTAIN OWNER DML function will not be used for the relationship.

Note: Be sure to include an OWNER pointer for any entity that participates as a child in more than one relationship since the child entity is probably an entity created to implement a many-to-many relationship. In this case, the system will most likely need to access parent entities from the child entities regularly.

Pointers in indexed relationships

The parent of an indexed relationship has the following mandatory pointers:

• Next pointer— Points to the first occurrence of an SR8 entity (an internal entity used to hold the index)
• Prior pointer— Points to the last occurrence of an SR8 entity

For further information on the structure of an index, see Chapter 15, "Determining the Size of the Database".

The child entity occurrence of an indexed relationship has one mandatory and one optional pointer:

• Index pointer—This pointer is required; it is used to access the SR8 entity that owns a particular child entity occurrence.
• Owner pointer—This pointer is optional; it points to the parent of the relationship

For further information on the structure of indexed relationships, see Chapter 15, "Determining the Size of the Database".

For further information on indexed relationships, see CA IDMS Database Administration Guide.

Representing linkage

Represent relationship linkage on the data structure diagram by identifying the pointers to be used. For example, specifying NPO indicates that next, prior, and owner pointers are to be used.

For an indexed relationship, specify I or IO.