Identifying Services

Currently the direction is towards Services. This push is seen primarily in smaller and growing companies. If you look at bigger corporations who already have their business process developed, are they changing their entire application to make it as a service? Not really!!. In these corporations, still there are projects happening in the services part. If the mainframe application (few of them developed long back) need to make its core business process available to the company, Service would help here. The service that exposes business functionality can be exposed as a Service.

The important task is to find out what services are to be created and at what level do we expose it? The service should do a functionality that has business significance. We need to contextualize to the business scenario and then evaluate if the service does business function or not? Let’s take a scenario. A Web Dealer wants to allow users to buy the items from the user’s shopping cart. This can be exposed as a Service. This service however needs many other related services like removing items from the cart, charging the credit card, placing order in shipping system etc. For the Web Dealer, exposing a payment service doesn’t make business sense as it doesn’t perform valid business functionality. Similarly exposing a service to update the shipping system also doesn’t make sense as the user cannot request to ship the items directly. But for a payment company, making the payment against a credit card will be valid functionality. The point that I’m trying to make is that it’s based on the business functionality that the services need to be decided. Food for one can be poison for the other. In the above scenario, the Web Dealer exposes a service to buy items taking the user details, credit card details and payment details as input, perform the entire business operation and return the response back to the client. The Payment Company will expose the Payment Service. The Service of the Web Dealer can make finer calls to the Payment Service and achieve the functionality. The shipping service might be designed as a bean call or a service that is not exposed to external users which will be used by the Web Dealer Service. From a web dealer user perspective, it just made a call to Web Dealer Service and not multiple fine grained calls to multiple services to complete the transaction.

While identifying and designing the services, attempt can be made to make many fine grained services. This gives more reusability. But these fine grained services should not be exposed. These fine grained services should be composed together to a coarse grained service and exposed as a valid service. Exposing too many fine grained services causes too many issues, performance security and network load being few of them.

Every attempt should be made to make the service asynchronous in nature. This means the client should not be forced to wait till the service completes its execution. After the processing is complete, the Service can provide some means to tell the client about the status of the execution.

These are my view points. If you disagree or would like to suggest or debate, please leave your comments.