Data Dictionary
Data Dictionary is an organized file of details about the database in the DBMS. Data dictionary occupies physical space within a database in the DBMS system.
Data Dictionary stores information about the number of table in a database, number of fields in a table, name of the tables, name of the fields, data types of each field, default values or allowed values of each field, description of the field to understand what are the value types accommodated in that field, description of the table to understand what is the table about, description of the stored procedures for a table, details on the user defined functions, number of users to the database , how are the objects related to each other in the database, database performance statistics, database growth statistics, database user statistics and all information related to a database in the DBMS architecture.
There is no standard to mention what level of details can a data dictionary store or manage. However data dictionaries maintain all sort of information about the database but not the actual data in the tables. The key benefit of a data dictionary is that it maintains consistency throughout the large complex database systems.
We could develop a middle ware over the data dictionary of the database system to provide a high level data dictionary capacity. The middleware could help in extending the data model of the database with the use of entity relationship diagrams about the database entities. A developer or designer when implementing new database objects could learn the existence of similar database objects in the database with the help of these data dictionaries and take a decision of creating a new object or enhancing the existing object or re use the existing object itself.
Data Dictionary forms the back bone of any Database Management System.
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1 Response to “Data Dictionary”
1Netrista Khatam on Jul 9, 2009 :
You are correct Middleware can greatly extend the database model. One example is Virtuoso Universal Server. Virtuoso is a kind of universal middleware that allows one to pull in metadata definitions from databases in different vendor’s DBMSs. This metadata can then be exposed such that the different database tables appear to originate from one DBMS. Use of Virtuoso also allows you to alter catalog/schema structure, table naming conventions, and data types, primary keys, and so forth, which greatly enhances the ability of third-party apps–especially database client apps liked SQL Server Linked Servers–to query data contained in the virtual database. This type of middleware technology makes a variety of database integration or migration possible because it allows one to affect how the data dictionary is exposed to the querying application.