DDBMS Architectures?
Architecture of a system defines its structure i.ecomponents of the systems
function performed by each component
Mutual interaction among the components.
Major Architectures
- Client / Server
- Peer to Peer
- Multi databases.
Client Server Architecture
a) ClientThe client is any computer process that requests services from the server.
The client is also known as the front-end Application
The client application or front end, runs on top of the operating system and connects with the middleware to access services available in the network.
Several Third-Generation Language (3GL) and Fourth-Generation Language (4GL) can be used to create the front-end applications.
Most front-end applications are GUI-based to hide the complexity of the Client/Server components from the end users.
Functions
Query parsing
Recombining the results
Transaction locks management
Consistency checking of queries
b) Server
The server is any computer process providing services to the clients.
The server is also known as the Back-end Application
The server application, or back end, runs on top of operating system and interacts with the middleware to “listen” for client’s requests for services.
Unlike front-end client process, the server process need not be GUI-based.
Functions
- Query processing
- Query optimization
- Transaction management
- Storage management
c) Communication Middleware
The communication middleware is any computer process through which clients and servers
communicate and is also known as Communications Layer.
The middleware software is divided into three main components:
- Applications Programming Interface (API)
- Database Translator
- Network Translator
API
API is public to the client application.
The programmer interacts with middleware through the API provided by the middleware software.
The middleware API allows the client process to be database-server-independent.
Means that the server can be changed without requiring that the client applications be completely rewritten.
d) Database Translator
- „
- Translates the SQL requests into the specific database server syntax.
- The database translator takes the generic SQL request and maps it to the database server’s SQL protocol.
e) Network Translator
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Manages the network communications protocols.
Database servers can use any of the network protocols, such as TCP/IP or Net BIOS.
The network layer handles all the communications details of each database transparently to the client application.
Middleware Classifications
Database middleware software can be classified according to the way clients and servers communicate across the network.
The middleware software is usually classified as:
Message-Oriented Middleware (MOM)
Remote-Procedure-Call-based (RPC-based) Middleware
Object-based Middleware
Working
Client parses a user query and decomposes it into a number of independent sub-queries. Each subquery is sent to appropriate site for execution.
Each server processes its query and sends the result to the client.
The client combines the results of subqueries and produces the final result.
Types of client server architecture
Multiple client- single server
Multiple client-multiple server (2 implementations)
each client manages its own connection to the appropriate server or
each client knows of only its home server which then communicates with other servers as required.
Peer to Peer Distributed System
All nodes have the same role and functionalityAll machines are autonomous and loosely coupled
Harder to manage due to autonomy and loose coupling
Scalable and flexible in growing and shrinking
Multi-database System
Fully autonomous databases
Each local DBMS does not know about the other one
The MDBMS software layer translates the queries formulated with the help of the global data model and the global conceptual scheme into queries based on the local data model
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