Maintaining Consistent Schema - Red Hat DIRECTORY SERVER 8.1 - DEPLOYMENT Deployment Manual

Chapter 3. Designing the Directory Schema
3.4.8.3. Defining Attributes before Object Classes
When adding new schema elements, all attributes need to be defined before they can be used in an
object class. Attributes and object classes can be defined in the same schema file.
3.4.8.4. Defining Schema in a Single File
Each custom attribute or object class should be defined in only one schema file. This prevents the
server from overriding any previous definitions when it loads the most recently created schema (as the
server loads the schema in numerical order first, then alphabetical order). Decide how to keep from
having schema in duplicate files:
• Be careful with what schema elements are included in each schema file.
• Be careful in naming and updating the schema files. When schema elements are edited through
LDAP tools, the changes are automatically written to the last file (alphabetically). Most schema
changes, then, write to the default file 99user.ldif and not to the custom schema file, such as
60example.ldif. Also, the schema elements in 99user.ldif override duplicate elements in
other schema files.
• Add all the schema definitions to the 99user.ldif file. This is useful if your are managing the
schema through the Directory Server Console.

3.5. Maintaining Consistent Schema

A consistent schema within Directory Server helps LDAP client applications locate directory entries.
Using an inconsistent schema makes it very difficult to efficiently locate information in the directory
tree.
Inconsistent schema use different attributes or formats to store the same information. Maintain
schema consistency in the following ways:
• Use schema checking to ensure attributes and object classes conform to the schema rules.
• Select and apply a consistent data format.
3.5.1. Schema Checking
Schema checking ensures that all new or modified directory entries conform to the schema rules.
When the rules are violated, the directory rejects the requested change.
NOTE
Schema checking checks only that the proper attributes are present. It does not verify
whether attribute values are in the correct syntax for the attribute.
By default, the directory enables schema checking. Red Hat recommends not disabling this feature.
For information on enabling and disabling schema checking, see the Directory Server Administrator's
Guide.
With schema checking enabled, be attentive to required and allowed attributes as defined by the
object classes. Object class definitions usually contain at least one required attribute and one or more
optional attributes. Optional attributes are attributes that can be, but are not required to be, added
30