Last week, IBM published a set of specifications that aim to unify grid computing and web services. Most of the media chose to ignore this landmark event and instead reported 'yet another' standards battle between IBM and Microsoft.
Media attention was focused on the evident overlap between WS-Notification, one of the IBM-backed specs, and WS-Eventing, announced by Microsoft, BEA and Tibco the week before. But this was really just a sideshow to the main event. True, both specifications deal with publish-subscribe mechanisms for communicating information about changes in status of loosely coupled network participants. Eventually, they'll probably be combined into a single standard. But for the moment, there's no conflict between the two, because they're designed for use in quite distinct environments.
WS-Eventing has been conceived to add a publish-subscribe dimension to even the most loosely federated of service-oriented architectures. It neither expects nor demands any other relationships to exist between the resources concerned, beyond their adherence to basic web services standards like SOAP and HTTP.
WS-Notification, on the other hand, is explicitly part of a much broader set of specifications called Web Services Resource Framework. It is concerned with exchanging updates and alerts within a much more closely knit, grid-style services architecture. Strictly speaking, of course, this differentiation is only a matter of degree, and will eventually dissolve. But in today's enterprise architectures, the two specifications are likely to operate at entirely different levels and thus can happily coexist because they'll never cross each others' paths.
Much more interesting than this non-conflict is the proposal to marry web services and grid computing through the Web Services Resource Framework (WSRF) set of specifications. As its name suggests, WSRF makes grid resources available via web services, thus combining the powerful resource sharing of grid architectures with the loosely coupled ethos of service-oriented architectures.
WSRF comprises a number of separate sub-specifications, such as WS-Resource Properties and WS-Resource Lifetime. WS-Notification got separate billing only because it has additional supporters. As well as IBM, HP and the Globus Alliance, who teamed up on WSRF, WS-Notification has had contributions from Akamai Technologies, SAP, Sonic Software and Tibco. I find the inclusion of Akamai on this list particularly meaningful, since Akamai has been a pioneer of resource sharing over the Web since before the dawn of web services.
To wrap up, here's a quick rundown of news stories and resources relating to WSRF and WS-Notification:
Companies Seek to Marry Grid, Web Services As its title suggests, internetnews.com just about manages to keep its eye on the big story: "Grid infrastructures and applications can now be built using Web services specifications with the guidance of WS-Resource Framework and WS-Notification."
IBM proposes Web services spec The coverage at CNET News.com spells out in plain language what the WS-Notification spec aims to achieve: "provide a standards-based way to program business applications to automatically respond to events such as a drop in inventory level or hardware server failure."
IBM, Microsoft on opposite sides of standards fence Delving into the differences between the overlapping specs, searchWebServices obtains some useful comments from HP's Mark Potts on why WS-Eventing didn't fit the bill: "... from a management perspective, we really needed something that was a little bit richer than a peer-to-peer event mechanism."