The operating system can use message catalogs to store messages. Messages in a message catalog are grouped as sets. Each message has a unique number within a set. You can create a message catalog as a stream file, a source file member, or a user space object type from one or more source files.
Because you can store message catalogs as stream files, you can use directories to isolate messages for specific products or national language versions.
You can use both the Generate Message Catalog (GENCAT) command or the Merge Message Catalog (MRGMSGCLG) command to create or update a message catalog. When a message catalog exists, continued use of these commands updates a catalog by comparing the original messages to the messages in the source. New message text replaces specific messages without changing the other messages within the set. With these commands, you can add or delete messages from an existing set of messages. You can also delete sets of messages from an existing message catalog.