Like many others, I view the emergence of schema.org with a jaundiced eye... another example of large, powerful companies wielding their influence without regard to an open standards process. This particular case is interesting because it brings together the arch-rivals of search -- Google, Microsoft, and Yahoo -- into uncommon cause.
Standards typically prevail in mature markets where the threat to innovation by convergence has declined, and it is in the best interests of companies to share at least certain aspects of their infrastuctural specifications. This is far from the case in search -- the black arts of SEO have long since entered the stage of personalization, the secrets of which are perhaps among the most closely held in all of information technology.
So, it is surprising that the giants have agreed on a common approach to structured (meta)data, and unfortunate that the agreement has turned away from the open standard of RDFa and towards an alternative, internally-created approach authored within Google. But they don't call it free enterprise for nothing, and if the Giant stretches and rolls over, squashing a few thousands of person-years of open standards work in the process, the ground on its other side will open up in fertile opportunitites for those nimble enough to invade the resulting ecosystem. And the fields of technology are nothing if not fertile and nimble.
There is nothing much new in this -- the library community has been struggling for years to snuggle in close to the thrashing giant without being squashed, with indeterminate degrees of success: the jury is still out. So, what will happen? There will be winners and losers, of course... The poor will always be with us, but so too, the rich. But who will the winners and losers be?
As far as I can tell, the people screaming loudest about schema.org are the semantic web folks (of whom I count myself one). Dublin Core, my own deepest professional engagement, is positioned as an important vocabulary for semantic web use, and I was in the room with three other people (Dan Connelly, Jim Miller, and Bill Arms) when the RDF course was initially set. If all of the past 15 years of semantic web ennabling infrastructure is washed away by the the few, I won't be happy. Except that that isn't what will happen. RDF and Dublin Core may turn out to be casualties... we'll see. But the trajectory of the thinking, the deployment, and the exploitation of all that work is as inevitably a part of the future of search as it was a month or a year or five years ago.
If Schema.org is successful (likely, given the importance of SEO), there will still be metadata spam (more sophisticated than ever). There will be the difficulty of effective deployment of a complicated ontology that will require some of the organizational insights and arcane ontological skills of library backrooms.
Is your average webmaster going to become a knowledge organization specialist? Well, they already are in one sense, and pattern recognition (and replication) are basic to the skill sets of programmers and system managers. So, we can expect templates to be perfected and promulgated in areas of eCommerce and in the backrooms of large content purveyors, and they will probably improve search and display of search results on the Web.
Will they achieve semantic web goals? Perhaps incrementally, but I suspect not a lot. The goal is to sell more stuff, and optimization will be based on that. To expect semantic value to ooze from the seams of commercial advertising (no matter how structured) seems unrealistic.
It is disappointing that the ennabling infrastructures for these functions will not be the same (or, if they become so, it will have been at the expense of open standards development). But it may be that the nominal reasons offered by schema.org for growing their own technology are legitimate to a degree -- RDF took too long, and is too complicated for wide deployment (15 years is an eternity in web development cycles). It may also be that the schema.org approach will prove inadequate for the challenging tasks of expressing semantics (as opposed to simple search optimization). Or it may be that the elusive goals of wringing semantics from machine-to-machine data exchange is still far from our grasp.
Whatever happens, nothing about schema.org will magically make data coherent. That still happens in the minds of the people who practice the art of semantic declaration, and we have a long way to go to see those arts commodified. I suspect schema.org may contribute, but I hope I may be forgiven an inclination to root for the underdogs along the way.
Prayer plaques at a local shrine. Many years ago I purchased such a plaque and profanely scribbled "World Domination for Dublin Core" on the back. As metadata goes, we came close enough I suppose.