Designing the Data Structure › Data Structure List › Data Structure List Terminology › Properties of Indexes

Properties of Indexes

Each index in the database has the properties listed in the following list.

• Generic Name—A name for the index that is consistent throughout all of the technical designs. It is called generic because it is not DBMS specific.

  The generic name can be no more than 32 characters long.
  There is no reason to change this name in the Data Structure List.

• Name—During DDL generation and installation, this is the name of the index that will be created using the properties of this entry point.

  The transformation process creates a unique default name for each index in the Data Structure List. Unlike columns and tables, an index is not based on a single object from the conceptual mode, so CA Gen has little basis on which to form a meaningful name. As a result, the names given to entry points created during transformation appear as the letter “I” followed by a string of digits. Although they work properly that way, you may choose to change the name to something more meaningful.

• Unique—Indicates that the index will not permit duplicate key values. If the index is derived from a data model identifier, then it must remain unique.

  It is unusual to have more than one unique index for a table so review carefully before creating a second (or third) unique index.

• Cluster—If you want the table itself to be sorted into the same order as the index, so that performance may be improved for certain types of access, you would add a cluster index. Review the material about clustering for your DBMS.

  In several cases, the DBMSs attempt to put rows in the clustering order by only actually organizing every row in a clustering order after a reorganization.

• Primary—Marks the index as the primary key.

  The referential integrity process sets the primary key during transformation, retransformation, or a separate (RI) process.

  Each table has only one primary key, which is used as the foreign key in relationship implementation.

• Description—A freeform text field used to document the purpose of the index.