DBMS - Architecture
- Most users of a database system today are not present at the site of the database system, but connect to it through a network.
- We can therefore differentiate between client machines, on which remote database users’ work, and server machines, on which the database system runs.
- Database applications are usually partitioned into two or three parts. They are:
- Two – Tier Architecture.
- Three – Tier Architecture.
Two – Tier Architecture
- The application is partitioned into a component that resides at the client machine, which invokes database system functionality at the server machine through query language statements.
- Application program interface standards like ODBC and JDBC are used for interaction between the client and the server.
- The architectures described here are called two-tier architectures because the software components are distributed over two systems: client and server.
- The advantages of this architecture are its simplicity and seamless compatibility with existing systems.
- The emergence of the Web changed the roles of clients and servers, leading to the three-tier architecture.
Three – Tier Architecture
- Many Web applications use an architecture called the three-tier architecture, which adds an intermediate layer between the client and the database server, as illustrated
- The client machine acts as merely a front end and does not contain any direct database calls. Instead, the client end communicates with an application server, usually through forms interface.
- The application server in turn communicates with a database system to access data.
- The business logic of the application, which says what actions to carry out under what conditions, is embedded in the application server, instead of being distributed across multiple clients.
- Three-tier applications are more appropriate for large applications, and for applications that run on the World Wide Web.