The Subschema entry allows a program to access a subschema in the Common
  Data Dictionary/Repository under the schema name.

  Format -

   DB subschema-name WITHIN schema-name

      [ FOR database-name ] [ { THRU    } stream-name ]
                            [ { THROUGH }             ] .

1 - subschema-name

  references a subschema name in the Common Data Dictionary/Repository
  (CDD/Repository) under the schema name.

2 - schema-name

  references a schema name in the Common Data Dictionary/Repository.

3 - database-name

  represents a complete or partial file specification defining the
  database occurrence.  A database occurrence is a root file.  At run
  time, database-name points the Database Control System (DBCS) to the
  root file.

4 - stream-name

  represents the name of a stream. Signals the Data Base Control System
  (DBCS) that your run unit uses a stream, which allows access to
  multiple databases or subschemas.