Database Management System (DBMS) Basic Concepts

Database Administrator (DBA)

The DBA is a person or a group of persons who is responsible for the management of the database. The DBA is responsible for authorizing access to the database by grant and revoke permis­sions to the users, for coordinating and monitoring its use, managing backups and repairing damage due to hardware and/or software failures and for acquiring hardware and software resources as needed. In case of small organization the role of DBA is performed by a single person and in case of large organizations there is a group of DBA's who share responsibilities.

Database Designers

They are responsible for identifying the data to be stored in the database and for choosing appropriate structure to represent and store the data. It is the responsibility of database designers to communicate with all prospective of the database users in order to understand their requirements so that they can create a design that meets their requirements.

End Users

End Users are the people who interact with the database through applications or utilities. The various categories of end users are:

• Casual End Users - These Users occasionally access the database but may need different information each time. They use sophisticated database Query language to specify their requests. For example: High level Managers who access the data weekly or biweekly.

• Native End Users - These users frequently query and update the database using standard types of Queries. The operations that can be performed by this class of users are very limited and effect precise portion of the database.

For example: - Reservation clerks for airlines/hotels check availability for given request and make reservations. Also, persons using Automated Teller Machines (ATM's) fall under this category as he has access to limited portion of the database.

• Standalone end Users/On-line End Users - Those end Users who interact with the database directly via on-line terminal or indirectly through Menu or graphics based Interfaces.

For example: - User of a text package, library management software that store variety of library data such as issue and return of books for fine purposes.

Application Programmers

Application Programmers are responsible for writing application programs that use the data­base. These programs could be written in General Purpose Programming languages such as Visual Basic, Developer, C, FORTRAN, COBOL etc. to manipulate the database. These application programs operate on the data to perform various operations such as retaining information, creating new informa­tion, deleting or changing existing information.

Entity - Relationship Model

The Entity - Relationship Model (E-R Model) is a high-level conceptual data model developed by Chen in 1976 to facilitate database design. Conceptual Modeling is an important phase in designing a successful database. A conceptual data model is a set of concepts that describe the structure of a database and associated retrieval and updation transactions on the database. A high level model is chosen so that all the technical aspects are also covered.

The E-R data model grew out of the exercise of using commercially available DBMS's to model the database. The E-R model is the generalization of the earlier available commercial models like the Hierarchical and the Network Model. It also allows the representation of the various constraints as well as their relationships.

So to sum up, the Entity-Relationship (E-R) Model is based on a view of a real world that consists of set of objects called entities and relationships among entity sets which are basically a group of similar objects. The relationships between entity sets is represented by a named E-R relationship and is of 1:1, 1: N or M: N type which tells the mapping from one entity set to another.

The E-R model is shown diagrammatically using Entity-Relationship (E-R) diagrams which represent the elements of the conceptual model that show the meanings and the relationships between those elements independent of any particular DBMS and implementation details.

Features of the E-R Model:

1. The E-R diagram used for representing E-R Model can be easily converted into Relations (tables) in Relational Model.

2. The E-R Model is used for the purpose of good database design by the database developer so to use that data model in various DBMS.

3. It is helpful as a problem decomposition tool as it shows the entities and the relationship between those entities.

4. It is inherently an iterative process. On later modifications, the entities can be inserted into this model.

5. It is very simple and easy to understand by various types of users and designers because specific standards are used for their representation.