Infoworld:

"[Q] What is the main challenge when it comes to exposing business logic as a Web service?

[A] Because a lot of applications are monolithic, you can't just pull out a useful piece of logic in the middle and make it do something useful. Part of the problem is that these applications aren't made out of discrete services. And if you don't have discrete services in the first place, it's very difficult to expose them as Web services."