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Chapter 1. Database System > Classification of DBMSs - Pg. 19

DATABASE SYSTEM 19 1.13 CLASSIFICATION OF DBMS S The DBMSs can be classified into different categories on the basis of several criteria such as the data model they are using, number of users they support, number of sites over which the database is dis- tributed, and the purpose they serve. Based on Data Models The various data models have already been discussed. Learn More Depending on the data model they use, the DBMSs MYSQL and PostgreSQL are open source can be classified as hierarchical, network, relational, object-oriented , and object-relational . Among these, (free) DBMS products that are supported the hierarchical and network data models are the by third-party vendors with additional ser- vices. older data models and now known as legacy data models . Some of the old applications still run on the database systems based on these models. Most of the popular and current commercial DBMSs are based on relational data model. The object-based data models have been implemented in some DBMSs; however, have not become popular. Due to the popularity of relational databases, the object- oriented concepts have been introduced in these databases that led to the development of a new class of DBMSs called object-relational DBMSs. Based on Number of Users Depending on the number of users the DBMS supports, it is divided into two categories, namely, single-user system and multi-user system. In single-user system the database resides on one computer and is only accessed by one user at a time. The user may design, maintain, and write programs for accessing and manipulating the database according to the requirements, as well as perform all the user roles. The user may also hire database system designers to design a system. In such a case, the single user performs the role of end user only. However, in most enterprises the large amount of data is to be managed and accessed by multiple users and thus, requires multi-user systems . In multi-user system, multiple users can access the database simultaneously. In multi-user DBMS, the data is both inte- grated and shared. For example, the Online Book database is a multi-user database system in which the data of books, authors, and publishers are stored centrally and can be accessed by many users. Based on Number of Sites Depending on the number of sites over which the database is distributed, it is divided into two types, namely, centralized and distributed database systems. Centralized database systems run on a sin- gle computer system. Both the database and DBMS software reside at a single computer site. The user interacts with the centralized system through a dummy terminal connected to it for informa- tion retrieval. In distributed database systems , the database and DBMS are distributed over several computers located at different sites. The computers communicate with each other through various communication media such as high-speed networks or telephone lines. Distributed databases can be classified as homogeneous and heterogeneous. In homogeneous distributed database system, all sites have identical database management system software, whereas in heterogeneous distributed database system, different sites use different database management system software. Based on the Purpose Depending on the purpose the DBMS serves, it can be classified as general purpose or specific pur- pose . DBMS is a general purpose software system. It can; however, be designed for specific purposes

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