![]() It may happen that the structure of the database has to be changed, such as to add new attributes or to remove some obsolete ones. SELECT * FROM SYSOBJECTS WHERE TYPE='U' AND NAME LIKE '%LOAN%' Ī data dictionary can be either active or passive. SELECT * FROM DBA_TABLES WHERE TABLE_NAME LIKE '%LOAN%' Making an educated guess that the table most likely has the word "LOAN" in it, he would issue the following query on the data dictionary (the first query is for an Oracle DB, while the second is for an SQL Server DB): However, it can only do this via the data dictionary created for that particular database.įor instance, following the above bank's database example, the administrator wants to determine which table holds information about loans. For example, the Oracle DB software has to read and write to an Oracle DB. Names of all indexes and the columns to which the tables in those indexes relate.Ĭonstraints defined on tables, including primary keys, foreign-key relationships to other tables, and not-null constraints.Īdditional physical information about the tables including their storage location, storage method, etc.įor example, a commercial bank's database containing information about clients can have attributes for client name, birth date, street address, financial savings, account and credit card number, loans, etc.Įach attribute occupies a row in a spreadsheet, while various columns provide additional elements that describe that attribute (whether it’s optional or required for a record, the type of data, its location, etc.).Ī data dictionary might look like the one below:įor most relational database management systems (RDBMS), the database management system software needs the data dictionary to access the data within a database. Names of all tables in the database and their owners. ![]() ![]() In a relational database, the metadata in the data dictionary includes the following: A Data Dictionary contains information about attributes or fields of a certain data set.
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