A dbms can use several kind of data structure as a part of physical system implementation. Each structure has its own importance. Following are some common data structure.
(1)Data Files: Data files contain the data portion of the database.
(2)Data Dictionary: Information pertaining to the structure and usage of data contained in the database, the metadata, is maintained in a data dictionary. The data dictionary is a database itself, documents the data. Each database user can consult the data dictionary to learn what each piece of data and the various synonyms of the data fields mean. In a system where the data dictionary is part of the DBMS(Integrated system) the data dictionary stores information concerning the source of each data-field value, the frequency of its use, and an audit trail concerning updates, including the who and when of each update.
Currently data dictionary systems are available as add-ons to the DBMS.
The data dictionary stores
Names of relations
Names of the attributes of each relation
Domains and lengths of attributes
Names of views defined on the database, and definitions of those views
Names of authorized users
Accounting information about users
Number of tuples in each relation
Method of storage used for each relation
Name of the index
Name of the relation being indexed
Attributes on which the index is defined
Type of index formed
(3)Indices: these are used to provide fast access to data items that hold particular values.
(4) Statical data: it stores the statical data about the data stored in the data base, like no. of records, blocks etc. in a table.
