Using Caché Objects - InterSystems Documentation

Indices
Data
Specifies additional properties to store in the index. By default, no additional data is
included.
Description
Extent
Provides an optional description of the index; Caché does not use this description.
By default, indexes have no description.
Specifies that the index identifies which objects belong to the extent of the class.
Extent indexes do not contain properties; they are strictly used to identify members
of the extent. By default, an index is not an extent index. If you are using bitmap
indices, there is no need to define an extent index: a bitmap extent index is automatically
maintained whenever any bitmap index is defined.
IDKey
Specifies a property or set of properties to use as the ID portion of the OID instead
of the default ID. An ID key must have unique values for each object in the class.
These values cannot change over the life of the objects. By default, an index is not
an ID key.
PrimaryKey
Properties
Specifies that this index is reported as the Primary Key to SQL. Any index defined
as a primary key must contain unique values for each object. By default, an index is
not a primary key.
Specifies the property or list of properties to include and sort upon in the index. An
index must include at least one property.
Type
Specifies whether this is a standard index (the default) or a bitmap index.
Unique
Specifies that each object has a unique value for the property or combination of
properties in the index. By default, an index is not constrained to unique values. You
cannot use the unique keyword with a bitmap index.
64 Using Caché Objects