How Oracle Uses the Data Dictionary (262)

Data in the base tables of the data dictionary is necessary for Oracle to function.
Therefore, only Oracle should write or change data dictionary information. Oracle
provides scripts to modify the data dictionary tables when a database is upgraded or
downgraded.

During database operation, Oracle reads the data dictionary to ascertain that schema
objects exist and that users have proper access to them. Oracle also updates the data
dictionary continuously to reflect changes in database structures, auditing, grants, and
data.

For example, if user Kathy creates a table named parts, then new rows are added to
the data dictionary that reflect the new table, columns, segment, extents, and the
privileges that Kathy has on the table. This new information is then visible the next
time the dictionary views are queried.

Oracle 如何使用資料字典
1. 資料字典基表中的資料是 Oracle 正常工作所必須的
2. 在資料庫執行期間，Oracle 透過資料字典內的資訊來確定方案物件是否存在，以及使用者是否具備相應的權
限。Oracle會持續地更新資料字典，以便反映資料庫在結構，資料，授權等方面的變化

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