1. What is Middleware?

2. How is a database connection between a client and a server established?

3. What is the advantage of ODBC?

Middleware is software that runs between client and server processes. It is the "glue" between the client and server, which makes it possible for them to communicate to each other. Middleware is written in such a way that the user never notices it's presence. It delivers secure and transparant services to users.

There are several types of middleware services.

• Remote Data Access (RDA), which implements a RDA protocol for sending data manipulation language statements to an appropriate database server for processing and transporting the result back to the invoking process.
• Remote procedure calls (RPCs). RPC is used in most network operating system services.
• Message-oriented middleware (MOM). MOM can be used as a mechanism for storing and forwarding messages queuing.It can be used when client and server processes communicate asynchronously.
• Object Request Brokers(ORBs). A standard implementation of the ORB standard is CORBA. ORB makes it possible to invoke a remote object by allowing a source object to send a message to that remote object.
• Distributed transaction processing (DTP). This type of mechanism use execution semantics to interact between the client and the server.

According to our system administrator our school uses a Microsoft SQL Server to store data about user accounts into a database. The system administrator uses a Windows 95 Client to manipulate the database. The SQL server runs on a Windows NT machine, which is located somewhere in the building.

When you observe this situation you might think that you only need a client running on your local machine and a server application running on the server to manage the database. But if you take a closer look, you see that this is not true. In fact you need:

• A client program which is a front end for the user.
• DBMS, Database Management System. In our case: Microsoft SQL Server.
• An RDA standard. In our case: ODBC, Open Database Connectivity Driver.
• A database server.
• A good functioning network. Additional hardware like network cables and cards are beyond the scope of this presentation.

In this section we describe how the connection between a client and a server is established. If you want to communicate between the client and server than both machines must run ODBC drivers to communicate with each other.

What is the advantage of ODBC?

ODBC stands for Open Database Connectivity. It is a standard which makes it is possible for any database application that supports ODBC to manage the databases which also supports ODBC with for example SQL statements.

Once you have the ODBC driver in place users can gain immediate access to your DBMS. If you write an application which supports the ODBC standard, you don't have to worry about how to approach the database. For instance: A Microsoft Client Application which supports ODBC can communicate with an Oracle Database which also supports ODBC. ODBC makes sure that the commands are converted in a proper way.