SOA Applications: Leveraging Existing Applications

It's highly likely that the bulk of existing applications do not support XML and web services – whether these applications were written in-house or packaged. While you may choose to decommission some of these applications, many others will remain in service. As such, it is necessary to formulate a strategy to leverage and service-enable your existing application assets as you move to create new SOA applications environment.

There are a number of different approaches to this. One approach is to hand code web service wrappers around the existing application when needed. The advantage to this approach is that you can use this layer to re-factor the service to be more business focused. The disadvantage is that it is can be time consuming and difficult to make a scalable, reliable, and robust hand-coded service wrapper.

The alternative is to use packaged integration products to service-enable the existing application. This may be an EAI or ESB solution or an adapter which directly converts the existing application into Web services in a single step. The advantage of these solutions is they can produce a more robust result. The disadvantage is that they don't make it easy to re-factor the service – the existing application appears to be web service enabled, but the interfaces are not necessarily the right level of business granularity. For example, the web service might have separate operations for creating "blank" orders and then populating the order with line items – in contrast a well designed ordering service would allow you to create a complete order with a single operation. This is a prime example of the difference between a technical service (designed the way it is for purely technological reasons) and a business service (designed to map to logical operations that the business performs).

The bottom line is that there are different ways to incorporate your non-Web services applications into your SOA applications environment. The best approach is often to combine the techniques list above: use an adapter, EAI, or ESB to directly service-enable the existing application as technical services then write a business service layer around the technical services using your choice of platforms.

For More Information About Building SOA Applications

Find out how to leverage existing applications as part of your move to a SOA applications environment: download the free webinar, Implementing a Successful SOA Pilot Program