A draft version (0.11) of the foundational framework for Data Center Markup Language (DCML) has been published.
I'm very critical of DCML's direction in this post; let's lay out my assumptions at the top:
1. DCML is aimed at large-scale enterprise IT, capitalist organizations with a strong and pragmatic emphasis on value proposition -- not academia.
2. DCML is not solving a research problem. It is not even solving a software engineering problem. It is a solution for a data management problem.
3. Large-scale enterprise IT is most comfortable with the relational database, and has built substantial infrastructure around data management using this platform. Object-orientation is restricted to software; object-oriented data management has failed to date. XML-based data management is going the same direction.
4. To the extent RDF is used, it will alienate the very customers that DCML is seeking: IT enterprise architects charged with evaluating new technologies and applying them to business problems.
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As reported, DCML is based on RDF from the W3C, which I find unfortunate; this semantics is even further from the experience of mainstream IT professionals than UML and object orientation is.
Let's be clear however (especially for my itsm-l readers): this spec explicitly references the concept of configuration management, which the OMG has been somewhat tardy in addressing. It clearly is aimed at a significant, if not core, domain of the ERP for IT problem.
The DCML effort does recognize that it needs a visual formalism, and UML is mentioned as a possibility pending the OMG's establishment of the Ontology Definition Metamodel (ODM). However, this is by no means a satisfactory solution. The DMTF framework has some characteristics of a meta-meta-model, and layering such abstraction on top of the ODM which in turn would be layered on top of the OMG's Meta-Object Facility - ugh!! Three layers of intellectually challenging abstraction before any meaningful data structures are expressed?
I'll have some further comments after I review the spec in detail. But this may require me to break down and burn some valuable time coming up to speed on RDF, which in all honesty I'm not too thrilled with. I'm somewhat of a stick in the mud who believes that the relational model and object orientation are quite enough in the way of core abstract semantics, thank you very much...
RDF comes out of the artificial intelligence community and from what I have seen, it's just plain overkill for the internal IT problem domain. I admit to having some homework to do in this area. However, if an obsessive-compulsive like me (writing this on a Saturday night) is reluctant to climb this hugely nontrivial learning curve, how will DCML ever be sold broadly? I don't buy the argument it's just for the tools vendors; large, sophisticated IT shops will need to grapple with it first hand as they try to drive real value out of DCML-based tools.
With all due respect to the information theorists working in the OMG and W3C, I feel I have to keep pointing out that most enterprise IT data management practices are based on relational databases and SQL. Object orientation is making some headway, but OODBMSes failed and most OO programmers still map to relational data structures. XML is having decidedly mixed success; as a tactical serialization format it is passable (albeit with performance issues); as a primary data definition language it is no substitute for relational modeling, and is being shunted aside by most data practitioners for this reason (this assertion based on numerous conversations I had at the last DAMA/Wilshire conference). The influence of relational pioneers Ted Codd and Chris Date is still strong, and XML is viewed as simply a throwback to IMS.
RDF is yet another fundamental data structure paradigm, with its own query languages, schema definition, and so on. SQL won't work unless the RDF structures are mapped into a relational database. This alone with drive away 90% of potential customers IMHO ("I can't use Crystal Reports? What the h*ll are they thinking?"). As a practitioner in a $27bn enterprise, I see object orientation struggling for acceptance on the data management side, let alone RDF. Existing repository vendors such as ASG, MetaMatrix, Adaptive, DAG, and others will have to re-tool significantly, or RDF tooling will perhaps require XML databases (a non-starter with most DBA teams, unless based on existing products - admittedly, the major RDBMS vendors are getting very strong with XML support). But even if the base persistence/querying are solved, real RDF repositories (with supporting frameworks, versioning, audit trails, delta capture, and everything else required by a robust repository) will require significant effort.
Never underestimate the costs of a new paradigm: core infrastructure tooling, steep learning curves for senior staff, shortages of qualified personnel: and for what? A non-deterministic, AI-based data management paradigm? Where is the requirement for such hairy complexity in the internal IT problem domain? The (meta) data may have deep inheritance, deep composition, and a lot of recursion -but first-order predicate logic works just fine for all this.
For further commentary on DCML, see here.
For an interesting perspective on how RDF compares to relational data management, see Data Modeling, Left and Right by Philip Engle. Frame logics? Higher order predicate logics? Urrgghhh.....
-Charlie
