THE DATA DICTIONARY AND THE SYSTEM CATALOG
Data dictionary provides a detailed description of all tables found within the user/designer-created database. It contains the attribute names and characteristics for each table in the system. In short it contains metadata
As in table below
System catalog contains metadata .the system catalog can be described as detailed system data dictionary that describes all objects within the database, including data about table name, the table s creator and creation date, the number of columns in each table, the data type corresponding to each column, index filenames, index creators, authorized users, and access privileges. Current relational database software generally provides only a system catalog, from which the designer s data dictionary information may be derived.
In effect, the system catalog automatically produces database documentation. As new tables are added to the database, that documentation also allows the RDBMS to check for and eliminate homonyms and synonyms.
Homonyms indicate the use of the same attribute name to label different attributes. For example, you might use C-NAME to label a customer name attribute in a CUSTOMER table and also use C-NAME to label a consultant name attribute in a CONSULTANT table.
Synonym is the opposite of homonym and indicates the use of different names to describe the same attribute.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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