The directory server supports multiple methods to extend the schema. The schema files are a set of LDIF files located in the install-dir/config/schema directory. Do not modify these files directly, because doing so can result in unpredictable server behavior.
You can extend the schema as follows:
Extend the schema over LDAP. Define your schema extensions, write the definitions to an LDIF file, and then add the custom schema extensions by using the ldapmodify command. When you use this method, the directory server automatically writes the new schema definitions to a file, 99user.ldif. If you want to specify a different schema file, include the X-SCHEMA-FILE element with the name of your schema file. For example, as part of your attribute type definition, include the element X-SCHEMA-FILE '98myschema.ldif'.
Create a custom schema file. Create a custom schema file with your definitions, save it as 98myschema.ldif, and then move the file to the install-dir/config/schema directory.
Modify an existing schema file. You can add a custom schema extension to an existing custom schema file, such as 99user.ldif.
When adding new schema elements, all attributes must be defined before they can be used in an object class.
If you are creating several object classes that inherit from other object classes, you must create the parent object class first.
Each custom attribute or object class that you create should be defined in only one schema file.
When defining new schema definitions manually, the best practice is to add these definitions to the 99user.ldif file or to your designated schema file.
The directory loads schema files in alphanumeric order with numbers loaded first, so you should name custom schema files as follows: [00-99]filename.ldif.