Friday, June 6, 2008

Outsourcing Business Capabilities

One of the commonly cited benefits of SOA is it gives organisations greater flexibility in outsourcing business capabilities. This is by virtue of the fact that organisations can leverage Web services as a foundation technology for B2B communications across organisational boundaries.

However one common misconception that exists is that a Web service interface that sits at the organisational boundary coincides with the boundary of a business service. This is in fact often not the case.

Consider an online retail business that sells products via an online store. Let's assume that the business also accepts orders by mail (either by snail mail or email) and telephone. The Sales service would include the online store Web application, as well as some kind of internal application leveraged by call centre operators that process orders by mail and telephone.

A possible Sales service architecture is illustrated below.


So what happens if at some point the business decides it can get better value from outsourcing its online sales channel to eBay? Well clearly the entire Sales service has not been outsourced. We end up with an architecture similar to that illustrated below.


Here we have a single service spanning organisational boundaries. The interaction between eBay and the components still hosted in house occurs inside the Sales service, but across organisational boundaries. The service contract of the Sales service remains unchanged.

No other service in our business need know that the online sales channel has been outsourced. Just as importantly, no service is dependent specifically on eBay. If at some point we decided to replace eBay with another provider, this would constitute only a change in the implementation of our Sales service.

Moreover, if we decided to branch out and leverage multiple third party online sales channels, this would involve only a change in the implementation of our Sales service.

Just because eBay exposes a Web service interface as an integration point for retail businesses doesn't mean that we should expose that interface directly to our other services in our enterprise. eBay's Web service interface is designed as a point of integration. No more, no less.

Business capabilities are unique to each business. Before outsourcing to eBay, our organisation had its own distinctive sales processes that evolved independently of sales processes in other organisations. Although there may be similarities, there will always be subtle differences.

Furthermore, our organisation will wish to retain the ability to tailor and evolve its sales processes as it sees fit. The business certainly won't appreciate terms being dictated by eBay.

We also want to be able to control the service level agreements (SLAs) (such as performance and reliability) upheld by our Sales service. eBay's Web service interface is based on synchronous request-reply interactions over an unreliable network (the Internet), effectively meaning there are no guarantees of availability or performance. Obviously we cannot expose other services within our enterprise to such poor SLAs.

Something else to consider is that eBay's Web service interface is potentially subject to change. We need to shield our other services from such potential changes. As such, we certainly don't want to couple our services directly to eBay's Web service contract.

Furthermore, what if we wish to outsource our online sales channel to a business that isn't quite so technologically savvy, providing an interface in the form of CSV files transferred via FTP? We certainly can't directly expose that as a service within our enterprise. What if we wish to partner with an organisation that offers only a REST based interface?

The point I am making is that people get tempted to directly expose Web services (of either of COTS applications or partner organisations) to other services within their organisations, simply because they are Web services. Do not do this. The provision of Web services is entirely coincidental and solely a result of the need for interoperability.

What is needed is a layer of abstraction between the partner organisation's Web service interface and the service contract exposed within our enterprise. This layer of abstraction gives our organisation the flexibility to have control over its sales processes and SLAs.

More on this example in my next post, so stay tuned!

18 comments:

Captain Ramen said...

Something else to consider is that eBay's Web service interface is potentially subject to change. We need to shield our other services from such potential changes. As such, we certainly don't want to couple our services directly to eBay's Web service contract.

In fact, it is guaranteed to change about once every two weeks. You can still submit web service calls using an older schema version. However, eBay changes its lowest supported schema version every two weeks also. You have about a year to upgrade your wsdl.

jose said...

That is the anticorruption layer Eric Evans talks about.

Bill said...

Indeed.

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