The n-tier client-server architecture used for the shopping cart web application, which is discussed in the earlier section, is an ideal example of a distributed client-server architecture. Distributed architectures typically have some kind of backend host components (such as Mainframe, Database server, and so on), an intelligent client in the frontend, and multiple agents in the middle, which takes care of all activities pertaining to transactions like transaction processing, security, handling messages, and so on, and a network for communication.

Some of the key concepts associated with distributed architectures are as follows:

• Transaction processing: Transaction processing is the automated processing of transactions in order to update a shared database. A transaction processing application in general will have many users who are concurrently interacting with the system in order to process business transactions on a shared database.
• Transaction processing monitor (TP monitor): The main task of the TP monitor is to manage the flow of transactions through a client server system efficiently. The TP monitor also works to ensure that simultaneous transactions which are happening on a shared database do not cause any inconsistency to the data which is present in the database.

TP monitors also provide the following functions:

• They help in setting up back and forth connections between client and server components
• They provide services that help in transaction-tracking, load balancing, and the capability to restart servers and the queues present in them automatically