Middleware Technologies [MCA II Yr, Anna University] by Roy Antony Arnold

1. File Server
2. Database Server
3. Transaction Server
4. Groupware Server
5. Object Server
6. Web Server

1. File Servers

• The client passes requests for file records over a network to the file server.
• This is a very primitive form of data service.
• File Servers are useful for sharing files across a network.
• These are acting as a repository of documents, images, engineering drawings and other large data objects.

2. Database Servers

• The client passes SQL requests as messages to the database server.
• The result of each SQL command are returned over the network to the client.
• The code in the server process will processes the SQL request and the data reside in the same machine.
• Distributed database servers may increase the efficiency of the processing power.
• These servers provide the foundation for decision-support systems that require adhoc queries and flexible reports.

3. Transaction Servers

• 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 network exchange consists of a single request/reply message.
• The SQL statements either all succeed or fail as a unit. These grouped SQL statements are called Transactions.
• The server component usually consists of SQL transactions against a database
• These are called Online Transaction Processing or OLTP.
• OLTP applications also require tight controls over the security and integrity of the database.
• Two forms of OLTP: based on the TP Monitors provided by the OLTP Vendors
  • TP Lite
  • TP Heavy

  

4. Groupware Servers

• Groupware addresses the management of semi-structured information such as text, image, mail, bulletin boards, and the flow of work.
• These client/server systems place people in direct contact with other people.
• Lotus Notes is the Leading Example.
• In most cases, applications are created using a scripting language and form-based interfaces provided by the vendor.
• The communication middleware between the client and the server is vendor-specific.

5. Object Servers

• The client/server application is written as a set of communicating objects.
• Client objects communicate with server objects using an Object Request Broker (ORB).
• The client invokes a method on a remote object.
• The ORB locates an instance of that object server class, invokes the requested method, and returns the results to the client object.
• Server objects must provide support for concurrency and sharing. The ORB brings it all together.
• Example: Digital’s Object Broker, IBM’s SOM 3.0, Sun’s NEO, HP’s ORB Plus, Expersoft’s Power Broker, Microsoft’s DCOM or Network OLE.

6. Web Servers

• WWW is the first truly intergalactic client/server application.
• This model of client/server consists of thin, portable, “universal” clients that talk to Superfast Servers.
• The clients and servers communicate using an RPC-like protocol called HTTP.
• This protocol defines a simple set of commands, parameters are passed as strings.
• The collection of HTML documents are stored in the Web Server.