What are Transaction Processors?

Transaction processors (TPs), also called TP monitors, are one of the oldest forms of middleware. Transaction processors provide execution and management environments for transactions, here defined as logical units of process that serve a specific business function. TPs also manage the interoperability of transactions. The primary purpose of TPs is to ensure that transactions are processed to completion, or to take appropriate actions if an error occurs. TPs are especially important in three-tier architectures^[1] that employ load balancing. Why? In the three-tier model, a transaction may be forwarded to any of several servers. TPs can offer load-balancing operations, forwarding transactions to different servers based on their availability. TPs therefore provide a number of important services: security, availability, and transaction handling. One of the first transaction processors was IBM's CICs, which is discussed below.

Short for Customer Information Control System, CICS was originally developed to provide transaction processing for IBM mainframes. CICS controls the interaction between applications and users and lets programmers develop screen displays without detailed knowledge of the terminals being used. CICS is also available on non-mainframe platforms. For practically any major eBusiness project taken on by the Fortune 1000, there will probably be a need to integrate with a CICS-based application. CICS is seldom used, however, as the core transacting software for modern eBusiness.

The predominant consideration here is age. Because TPs are the oldest form of middleware, transaction processing is a tried and true technology. However, TPs have generally been supplanted by more robust and flexible integration technologies. Usually TPs are limited to a given computing architecture and a local set of programs. The need for cross-network and cross-application processing of calls for distributed object integration, XML, and message-based integration. In most cases, TP-based applications may be used to integrate into eBusiness applications, but seldom are they used as a core integration engine for eBusiness. The next lesson discusses a kind of middleware package, Enterprise Application Integration (EAI).

[1] Three-tier architecture: A special type of client/server architecture consisting of three well-defined and separate processes, each running on a different platform.