XSD Versioning and Semantic Changes
Tim has an interesting post here about dealing with semantic changes in existing interfaces on Web Services (continuing from his posts here, here, and here). I found this particularly interesting because we followed a very similar approach on our last project.
In our case, we had a set of existing operations on a service with an existing client using it, and needed to extend it with new operations. That was no problem. However, during development we noticed that due to changes in a backend LOB application our services connected with a new field was needed some of the original operations. In particular, we needed the client to let us know on what TimeZone (or rather what the time shift from UTC) to use when registering the time some operations occurred. However, we required the original client didn't change.
What we ended up doing was basically making the new TimeZone field optional, and then introducing logic on the operations that checked if it was missing. If it was, instead of simply assuming a global default value, we actually queried our security configuration and extracted a default value for this field that was specific to the client making the call. This was possible because the services were using WS-Security for authenticating the caller. This way, we could actually set especific default values for other clients if needed. It worked very nicely overall and was remarkably easy to put in place.
Some of you might be wondering how we dealt with DST: We didn't. A explicit decision from the business side was made not to support it because of some complexity in the business side of things, and particularly because it would've required clients in other countries to make changes to existing infrastructure and the benefits just were not worth it. One thing we did learn from that experience was that handling date and time fields in webservices where consumers and service-providers are on different countries and time zones can be easily get quite tricky, and that the way .NET handles dates on WebServices does not make things any easier.
