William Vambenepe's blog

The CMDBF (CMDB Federation) group just released a first public draft of the specification. Here is a direct link to it (PDF, 1MB). That’s a very nice achievement for a group that was a bit slow to find its pace but has been very productive since the beginning of 2007. Having the interop test drive our efforts had a lot to do with it, this is an approach to repeat the next time around.

This spec will look a lot more familiar to people used to reading WS-* specs than to people used to reading ITIL manuals. The concepts and use cases are (hopefully) consistent with ITIL, but the meat of the spec is about defining interoperable SOAP-based message exchanges that realize these use cases. The spec is about defining SOAP payloads, not IT management best practices. Please adjust your expectations accordingly and you’ll like the spec a lot more.

The most useful and important part (in my mind at least), is the definition of the Query service (section 4). This is used in many interactions. It is used by clients to query a CMDB that federates many MDRs (Management Data Repositories). It is used by the clients to go interact directly with the MDRs is they choose to. And it is used by the federating CMDB to retrieve data from the MDRs. Even in the more static scenarios, in which data is replicated from the MDRs into the CMDB (instead of true federation with no replication), the Query service is still the way for clients to access federated data from the CMDB.

So, yet another query language? Indeed. But one that natively supports concepts that are key to the kind of queries most useful for CMDB scenarios, namely relationships traversal and types. This is a topological query language. I hope the simple example in section 4.2 gives a good example of what this means.

Neither SQL nor XPath/XQuery has this topology-friendly approach (which is not to say that you can’t create useful queries on CMDB data with these query languages). On the other hand, there is one query language that is inherently relationship-oriented, that has native support for the notion of class and that has received a lot more attention, interop testing and implementation experience than our effort. One that I would have loved for us to leverage in CMDBF. It’s SPARQL. But semantic web technologies seem once again to be doomed by the perception that they are too much “out there” despite all the efforts of its proponents to make them connect with XML and other non-RDF views of the world.

Final caveat, this is a first draft. It is known to be incomplete (you’ll find text boxes that describe known gaps) and not all features in the spec were tested at the interop. We need more interop, review and development before it is robust. And most importantly, a lot of the difficult aspects of federation aren’t sufficiently addressed (reconciliation, model differences, source tracing, administrative metadata…) But it is at a point where we think it gives a good idea of how we are approaching the problem.

Equipped with this foreword, I wish you a pleasant read.

This entry was posted on Thursday, August 2nd, 2007 at 10:36 pm and is filed under CMDB Federation, CMDBf, Everything, Specs, Tech. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.