The Middleware Platform

The term middleware refers to runtime system software, which is layered between the application programs and the operating system. It acts as a bridge to integrate application programs and other software components in an environment with multiple network nodes, several operating systems, and many software products. Middleware is needed to run client/server architectures and other complex networked architectures in a distributed computing environment. Therefore, the middleware should support directory services, message-passing mechanisms, and database gateways.

Most middleware falls into two major categories:

1. Distributed logic middleware supports program-to-program communication between two pieces of custom-written application code.

2. Data management middleware connects an application or DBMS on one platform with a DBMS running on another platform.

Middleware can also be used to enable "reach-through" queries from summaries in the BI target databases to the underlying detail data held in operational systems. To keep the cost to a minimum, a number of organizations are already using gateways to transfer data from multiple heterogeneous sources of server data to client workstations, as illustrated in Figure 2.3.

Figure 2.3. Gateway Example

DBMS Gateways

DMBS gateways, a form of middleware, are generally required to connect the different network architectures of desktop computers, remote clients , or small enterprise servers to industrial-strength enterprise servers.

Gateways fall into four major categories.

1. Point-to-point gateways provide access to only one type of DBMS. Vendors market each point-to-point gateway as a different product. A point-to-point gateway is easy to implement because it handles only one DBMS at a time. It is also a less expensive solution compared with the other three gateway solutions. However, when the organization requires access to multiple DBMSs, it needs multiple gateways. In that case, point-to-point gateways may not be a less expensive solution than using a universal gateway.

2. Gateways that can be used universally provide access to different types of databases on various platforms. Universal gateways require extensive effort to implement and maintain. As a result, these gateways become expensive.

3. Gateways using Structured Query Language (SQL) can access only "real" relational databases, not simulated ones. The SQL gateway translates the client request into the native SQL syntax used by the server's relational DBMS.

4. Gateways based on application programming interfaces (APIs) are driven by vendor specifications. One of the major gateways of this type is open database connectivity (ODBC). A number of ODBC vendors provide drivers for accessing databases residing on various servers.

Organizational data is distributed across multiple DBMS platforms, cooperating across a network with different instruction sets from multiple vendors. ODBC-enabled applications can access multiple distributed data sources concurrently via ODBC's common interface approach (Figure 2.4).

Figure 2.4. ODBC-Enabled Applications

Modules called database drivers can be added to link the applications to the DBMS of their choice. Database drivers consist of dynamic link libraries (DLLs) that applications can invoke on demand.