TECH TALK: Business to e-Business: 10 Transformations: Request-Reply to Publish-Subscribe
Information is the key driver for all decision-making. Software and networks today can ensure that information can be available across the organisation. From a manager’s point of view, there is perhaps too much information available. How does one ensure that the manager has the right information to make the decision?
The conventional way has been to use a “request-reply” approach. This “pull” approach fits in well with the client-server architecture. The client makes a request to a server, and the server responds with the appropriate information. For this to work effectively, it means that the client needs to keep polling the server, and perhaps set up trigger software for alerts when specific conditions are met. The problem with this approach is that if 100 people make a query for the same information, the server needs to send that information out to all 100 of them.
As the Internet makes possible a distributed architecture, a new technique can be used for delivering just the information a manager needs at the right time. This “publish-subscribe” approach ensures that information is just published once (multicast) on a network, and all those who have subscribed to receive that information can now do so. Writes Pete Loshin in Byte:
Sometimes referred to as pull software or smart-push software, publish-and-subscribe (PS) middleware enables information consumers to subscribe to particular messages (sometimes known as data events, to distinguish them from e-mail-type messages) while making it easy for information producers to publish data events. PS products can keep a lid on network traffic, even when there’s lots of data and many subscribers, by using message routers and multicast transmission to distribute information.
Publish-subscribe messaging is a many-to-many paradigm. It is ideal when there are multiple applications/clients to receive the same message or when a group of applications want to notify each other. In the networked world, this is going to be the norm.
An example of the two technologies is how we query for stock prices. Request-reply is how we are getting the stock quotes, even in personalized portfolios. At best, the browser can be set up to update the page frequently (through polling). With publish-subscribe, the computer will subscribe once to the stock price and will now receive all events that are published on the network whenever the stock price changes. Vivek Ranadive, CEO of Tibco, which pioneered the publish-subscribe technology, compares the two technologies:
In contrast to the passive “query-me” client/server technology, active publish/subscribe technology allows information about business events to be distributed in real-time across private and public networks.It can instantly and automatically deliver to everyone in your company’s environment the information each person needs to create maximum value for your customers.
Place your finger on a red-hot stove. If our nervous systems were request-reply, you’d learn the stove’s temperature the next time your nerves polled the stovetop. Fortunately, our nervous systems are event-driven, and they report the stove’s temperature instantly. Which nervous system would you want for your company?
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