There are two types of index sets: user-owned and system-owned. A user-owned index implements a logical relationship between the owner entity type and the member entity type. A system-owned index provides direct access to member record occurrences for performance purposes and as the name implies, its owner is a special SYSTEM owner record type. A system-owned index is often referred to simply as an "index."
If the DEPT-EMPLOYEE set is implemented as an index set, it is a user-owned index because the owner record type is DEPARTMENT. There will be one index structure for each occurrence of the DEPARTMENT record type.
There is always exactly one occurrence of a system-owned index set. The owner is a special CA-defined record and all occurrences of the member record type may be members. It is often used to provide a way to access member records by an exact or generic key value. For example, we may need to access departments by name instead of department id. A system-owned index called IX-DEPARTMENT has been defined with DEPT-NAME as the sort or symbolic key. The following figure illustrates this index.
|
Copyright © 2013 CA.
All rights reserved.
|
|