The DBMS_METADATA package provides interfaces for extracting complete definitions
of database objects. The definitions can be expressed either as XML or as SQL DDL.
Two styles of interface are provided:
■ A flexible, sophisticated interface for programmatic control
■ A simplified interface for ad hoc querying

数据库对象元数据
DBMS_METADATA 包为用户提供了获取数据库对象完整定义的接口。此包可以通过 XML 或 SQL DDL
的形式提供定义信息