1  –  catalog-expression

    Specifies the name of the default catalog for a multischema
    database. If you omit the catalog name when you specify an object
    in a multischema database, SQL uses the default catalog name.
    If you do not specify a default catalog name, the default is
    RDB$CATALOG.

    If you qualify the catalog name with an alias, the alias and
    catalog name pair must be in uppercase characters and you must
    enclose the alias and catalog name pair within double quotation
    marks.

    See the User_Supplied_Names HELP topic for more information on
    catalogs.

2  –  catalog-parameter

    Specifies a host language variable in precompiled SQL or a formal
    parameter in an SQL module language procedure that specifies the
    default catalog. The catalog parameter must contain a catalog
    expression.

3  –  catalog-parameter-marker

    Specifies a parameter marker (?)  in a dynamic SQL statement. The
    catalog parameter marker refers to a parameter that specifies
    the default catalog. The catalog parameter marker must specify a
    parameter that contains a catalog expression.

4  –  catalog-string-literal

    Specifies a character string literal that specifies the default
    catalog. The catalog string literal must contain a catalog
    expression enclosed in single quotation marks.