Chapter 4 Building Physical Diagrams

Index properties

You can modify an object's properties from its property sheet. To open an index property sheet, double-click its diagram symbol or its Browser entry. The following sections detail the property sheet tabs that contain the properties most commonly entered for indexes.

The General tab contains the following properties:

Property Description
Name Specifies the name of the item, which should be clear and meaningful, and should convey the item's purpose to non-technical users
Code Specifies the technical name of the object, which is used for generating code or scripts, which may be abbreviated, and should not generally include spaces
Comment Specifies a descriptive label for the index
Stereotype Sub-classification used to extend the semantics of an object without changing its structure; it can be predefined or user-defined
Owner Specifies the name of index owner. You choose an owner from a list of users, the index and table owners can be identical or different. An index can only have one owner at a time. This is normally the index creator.

Some DBMS allow you to define an index owner, either identical or different from the table owner. If the DBMS of the current model does not support index owners, the table owner will be automatically assigned to the index after switching to a DBMS that supports index owners.
Table Specifies the table to index
Type [Sybase IQ, and Oracle only] Specifies the type of index. You can choose between:

  • Bitmap – [Oracle] In a bitmap index, a bitmap for each key value is used instead of a list of row Ids
  • HG – [Sybase IQ] HighGroup indexes are used for GROUP BY, COUNT(DISTINCT) and SELECT DISTINCT statements when data has more than 1000 unique values
  • HNG – [Sybase IQ] HighNonGroup indexes make equality comparisons, SUM and AVG calculations very fast when data has more than 1000 unique values. Nonequality comparisons can also be done
  • LF – [Sybase IQ] LowFast indexes are used for columns that have a very low number of unique values. This index also facilitates join index processing. It is one of the two indexes allowed for columns used in join relationships
  • CMP – [Sybase IQ] Compare indexes are used for columns that store the binary comparison (<, >, or =) of any two distinct columns with identical data types, precision, and scale
  • WD – [Sybase IQ] Is used to index keywords by treating the contents of a CHAR or VARCHAR column as a delimited list
Unique Specifies whether an index is a unique index
Cluster Specifies that the index is a clustered index. A table cannot have more than one clustered index.

Note that clusters in Oracle 11 and higher are modeled as extended objects with a <<Cluster>> stereotype. For more information, see the DBMS-Specific Features chapter.

The following tabs are also available:

 

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