The servers can be classified based on the service they provide to the clients as described in the following section. File Servers: Wi...
The servers can be classified based on the service they provide to the clients as described in the following section.
File Servers:
With a File Server, the client typically passes requests for file records over a network to the file server. This is a very primitive form of data service that necessitates many message exchanges over the network to find the requested data. File servers are useful for sharing files across a network. They are necessary for creating repositories of documents, images and engineered drawings and other large data objects.
File Servers:
With a File Server, the client typically passes requests for file records over a network to the file server. This is a very primitive form of data service that necessitates many message exchanges over the network to find the requested data. File servers are useful for sharing files across a network. They are necessary for creating repositories of documents, images and engineered drawings and other large data objects.
Database Servers:
With a database server, the client passes SQL requests as messages to the database server. The results of each SQL command are returned over the network. The code that processes the SQL request and the data reside on the same machine. The server uses its own processing power to find the requested data instead of passing all the records back to the client and then letting it find its own data as in the case of the File Server. Database servers provide the foundation for decision-support systems that require adhoc queries and flexible reports.
Transaction Servers:
With a transaction server, the client invokes remote procedures that reside on the server with an SQL database engine. These remote procedures on the server execute a group of SQL statements. The SQL statements either all succeed or fail as a unit. These grouped SQL statements are called transactions.
With transaction server, the client/server application is created by writing code for both client and server component. The client component includes a GUI and the server component consists of SQL transactions against a database. These applications are called OLTP (Online transaction processing). OLTP applications require tight control over security and integrity of the database.
Groupware Servers:
Groupware addresses the management of semi-structured information such as text, image, mail and the flow of work. These client/server systems place people in direct contact with other people. Lotus Notes is the leading example of such a system and other applications include imaging, multiparty applications and workflow. In most cases, applications are created using a scripting language and form based interfaces provided by the vendor.
Object Servers:
With an object server, the client/server application is written as a set of communicating objects. Client objects communicate the server objects using an Object Request Broker (ORB). The client invokes a method on a remote object. The ORB locates an instance. The ORB locates an instance of that object server class, invokes the requested method, and returns the result to the client object. Server objects must provide the support for concurrency and sharing. The ORB brings it all together. Examples of commercial ORBs that comply with Object Management Group’s CORBA standard include Digital’s ObjectBroker, IBM’s SOM 3.0, Sun’s NEO. Microsoft is getting ready to ship its own ORB, which it calls Distributed COM (DCOM) or Network OLE.
Web Servers:
The World Wide Web is the first truly intergalactic client/server application. This new model of client/server consists of thin, portable, universal clients that talk to superfat servers. The web server returns documents when client ask for them by name. The clients and server communicate using an RPC protocol called HTTP. This protocols defines a simple set of commands, parameters are passed as strings, with no provision for typed data. In addition, the web and distributed objects are starting to come together. Java is the first manifestation of this new Object Web.
