摘要：
One of the most important parts of an Oracle database is its data dictionary, which is a ready-only set of tables that provides information about the database. A data dictionary contains:
- The definitions of all schema objects in the database (tables, views, indexes, clusters, synonyms, sequences, procedures, functions, packages, triggers, and so on)
- How much space has been allocated for, and is currently used by, the schema objects.
- Default values for columns
- The names of Oracle user 阅读全文