The schema extensions are implemented in a single attribute schema that is essentially a catalog of schema entries, each of which defines the format and function of an attribute type. The schema can be dynamically updated to create, modify, or delete schema entries.
The attribute schema is identified by the name xattrschema under the security junction point (usually /.:/sec) in the CDS namespace. Access to the attribute schema (hereinafter called simply schema) is controlled by an ACL on the schema object. The schema is propagated from the master security server to replicas, like other registry data. Since the attribute schema is local to a cell, it defines the types that can be used within the cell, but not outside the cell (unless the type is also defined in another cell).