In my recent book 'Beginning JavaServer Pages', I touch upon Web services in a project chapter. It is a JSP/JSTL/Web frameworks book, not a Web services book- so the treatment is introductory.
In this introduction, I mention two application area where Web service technologies are, and will be very significant. However, increasing it now seems that it might not be the same set of technologies.
The two areas are:
The first refers to all the EAI type stuff Web services does, or is capable of. This is also where there is a lot of vendor activity, and where all the WS-* specifications are targetted.
In the second area, REST is becoming increasingly significant. It is getting more grassroots support, but a lot less vendor support. In an earlier post, I mentioned how Yahoo's new API is REST only, and that Amazon has seen most of its developers prefer REST to SOAP. REST is much easier to use, and would even scale/perform better than its SOAP counterpart.
Yahoo joins the growing number of web sites exposing their API as Web Services. Their API is available from Yahoo Developer Network.
Interesting, they do not have a SOAP API, but only a REST based API. REST is getting very popular with developers, and Amazon has seen that 85% of their Web service API users, are using it via the REST interface.
REST (Representational State Transfer) is quite simple and elegant, with its resource 'nouns' (represented by a URL) and the four HTTP 'verbs' - GET/POST/PUT/DELETE mapping nicely to CURD operations. However while I can see it being successful in applications like the Yahoo search API, it is, IMO, not very appropriate when used in the context of integrating more complex applications.