command_context
    type:       $SCA_COMMAND_CONTEXT
    access:     read/write
    mechanism:  by reference

    An SCA command context.

 query_context
    type:       $SCA_QUERY_CONTEXT
    access:     write only
    mechanism:  by reference

    An SCA query context to be initialized. This value is passed as an
    argument to other SCA query routines (SCA$QUERY_xxx).