Could not use database file specified by <str>

  Explanation:  If you do not issue an explicit DECLARE ALIAS,
  ATTACH or CONNECT statement, SQL uses the database file
  specified by the logical name SQL$DATABASE.  Because the logical
  name SQL$DATABASE is not defined or does not refer to a valid
  database, SQL could not attach to a database.  See the messages
  following this message for more information.

  User Action:  Explicitly declare a schema before executing any
  statements which require a database, or define the logical name
  SQL$DATABASE to specify the database file you wish to use.