Over time, as you have used the Oracle database, you may have developed your own code for extracting metadata from the dictionary, manipulating the metadata (adding columns, changing column data types, and so on) and then converting the metadata to DDL so that you could re-create the object on the same or another database. Keeping that code updated to support new dictionary features has probably proven to be challenging.
The DBMS_METADATA API eliminates the need for you to write and maintain your own code for metadata extraction. It provides a centralized facility for the extraction, manipulation, and re-creation of dictionary metadata. And it supports all dictionary objects at their most current level.
Although the DBMS_METADATA API can dramatically decrease the amount of custom code you are writing and maintaining, it does not involve any changes to your normal database procedures. The DBMS_METADATA API is installed in the same way as data dictionary views, by running catproc.sql to run a SQL script at database installation time. Once it is installed, it is available whenever the instance is operational, even in restricted mode.
The DBMS_METADATA API does not require you to make any source code changes when you change database releases because it is upwardly compatible across different Oracle releases. XML documents retrieved by one release can be processed by the submit interface on the same or later release. For example, XML documents retrieved by an Oracle9i database can be submitted to Oracle Database 10g.