we see the idea of simplicity appearing over and over again when we analyze the advantages of various successful models and systems over their competitors/predecessors. HTML vs. SGML. REST vs. SOAP. Hibernate over EJB and Spring over J2EE. Extreme Programming's KISS philosophy and the New Jersey approach to design. Capitalism vs. Communism. hell, even Nike is going barefoot these days, and in the world of organized violence the paring down of "barred" holds and the mixing of styles is all the rage. common to all of these frameworks is the greater flexibility and creative freedom to allow human ingenuity its fullest expression. when the prime value of the global network that all of our lives are being woven deeper and deeper into is the aggregation and multiplication of human capital, i think that it's no accident that models which release human capabilities are gaining more and more prominence over those that attempt to control them.
what many people fail to realize about the RDF model of data is that it is a simpler and more general model of data than anything that has come before it. not RDF with schemas and ontologies and all that jazz. that's actually more complex than anything that has come before it. i'm talking about basic RDF. designed originally as a data model for the web, one key requirement had to be met: that any data anywhere on the globe, whether it be in relational databases, network databases, flat files, or what have you, could be mapped to it. consequently, what was produced was a kind of lowest common denominator of data models. a key concept here is that of the fundamental, irreducible unit of data as the simplest kind of statement (or, more precisely, in the language of mathematics: a binary relation). even C.J. Date - arguably second only to Codd as an authority on the relational model - acknowledged in a recent comment on "relational binary database design" that there is an argument for the binary relation being an irreducible unit out of which the n-ary relations which relational theory deals with can be composed. in his comment, he describes how a ternary (3 column) relation can be composed by "joining" 2 binary relations. by breaking down the nature of data into something a bit more granular to manipulate we gain a power and flexibility not unlike that envisioned by Bill Joy when he waxes philosophic about nanotechnology and its promise of the ability to create any physical thing by manipulating granular components of matter. indeed much of the progress in our understanding of matter has been driven by successive discoveries of increasingly more granular, or atomic, units of matter.
"No tuples barred" data kung-fu
there's another aspect of RDF that has practical consequences that make it a good fit for the web: it's "self-describing" nature. this aspect of RDF is not just something that was artifically designed in or layered on; it follows quite naturally from its reductionist foundations. since we effectively use the irreducible binary relation as a kind of building block to compose larger types of relations, each irreducible binary relation must have an independent existence apart from the compositional relationships it participates in. it must have a global identifier to be independently recognizable by the system. when the most granular components of even the most complex dynamic aggregations of data are identifiable as individuals with an independent existence, the effect is that the data becomes self-describing. contrast that with the relational model wherein columns are defined relative to a relation. columns cannot be said to exist independent of some relation of which they are a part.
when data is self-describing, schema becomes inessential. there are no RDBMS's that I'm aware of that allow data to be created that does not conform to some pre-defined schema. XML, on the other hand, another self-describing data format, does not require a schema to exist before you can create a valid XML document. while schema may be useful for enforcing/confirming some kind of organization of the data, it is not essential to the creation and manipulation of data.
this allows you to have a database that does not require the kind of bureaucratic planning that the database modeling exercise in a large organization can devolve into before being put into action. if it were a relational database, it would be as if there were no conceivable tuple barred from creation. it allows a level of responsiveness and agility in reacting to problems and creating solutions that simply isn't possible with today's RBMS technology, and with the bureaucracy that has developed in many corporate IT departments around the administration and development of such database systems.
such a system would be much like a database created in Prolog (which almost certainly had an influence on the design of RDF due to its early "knowledge representation" aspirations). in Prolog you can assert any fact, i.e. make any statement that you want without having the predicates predefined. any kind of higher-order structure or logic that exists among the facts, such as a graph connecting a set of binary relations, is an emergent property of a dataset that can be discovered through inference, but is never explicitly defined anywhere in the system. while some sort of schemata may serve as a guide to a user entering facts and rules in a Prolog database, prolog is not aware of it, and has no way of enforcing it. this is much the way that the human brain, indeed matter itself, works. while it's possible at higher levels of organization for both the brain and matter to create rigid molds into which things that don't fit the mold are not accepted, they don't fundamentally work this way. by the same token, it is possible to create RDF systems that ridigly enforce RDF schemas and ontologies, but i wouldn't recommend it. the bigger your world gets the more flexiblity you want. as your horizon expands, it becomes increasingly difficult to define a single schema that fits all data, and the web is about as big a data universe as you can get. the simpler model scales better.
a recent article in HBS Working Knowledge, entitled "How Toyota and Linux Keep Collaboration Simple", describes how "The Toyota and Linux communities illustrate time-tested techniques for collaboration under pressure". the article makes the point that both groups follow a minimalist philosophy of using the simplest, most widely available technologies to enable far-flung groups to collaborate. a minimalist, widely available database technology (i.e. available as a service over HTTP) could allow a kind of real-time programming capability to rapidly create programs that allow collaborators across different organizations to analyze and attack novel problems with unique data patterns in near real-time. the web database should be like a CVS for data, allowing programmers to work in parallel with different representations of data and to merge those representations, in much the way source code version control systems allow different representations of program logic to be worked on in parallel, and merged. like CVS it should provide a lineage of the changes made to those representations allowing them to be "rolled back" if necessary, giving coders the confidence to move forward quickly pursuing a path, knowing that it will be easy to backtrack if necessary. it would be the perfect database technology for agile development, founded on the Jeet Kune Do of data models:
JKD advocates taking techniques from any martial art; the trapping and short-range punches of Wing Chun, the kicks of northern Chinese styles as well as Savate, the footwork found in Western fencing and the techniques of Western boxing, for example. Bruce Lee stated that his concept is not an "adding to" of more and more things on top of each other to form a system, but rather, a winnowing out. The metaphor Lee borrowed from Chan Buddhism was of constantly filling a cup with water, and then emptying it, used for describing Lee's philosophy of "casting off what is useless."
The best of all worlds
recently i came across this interview in 2003 with Don Chamberlin, co-inventor of SQL. nowadays, he spends his time working out a query language for XML and thinking about how to unify structured data and unstructured data under one model, and the integration of heterogenous data with self-describing data models (the latter is exactly what RDF is a good simple solution for, and XML isn't). it ends with some interesting quotes by Mr. Chamberlin:
so are we are ready for a new data model? is the web indeed "Bachman's Revenge", and will the new data model be really a return to something old? in some ways, yes. the web, and RDF, do superficially resemble the hyperspace of Bachman's network data model. the hyperlink is a binary relation between two nodes, and both the network data model and RDF are based conceptually, to some extent, on a graph model of data. this is directly attributable to the binary relation's fundamental role in graph theory. but RDF is also fundamentally different. in Bachman's network model it was "records" that were hyperlinked. these records looked more like the n-ary relations of the relational world (though they were never rigorously and formally defined as such). thus, there was a fundamental inconsistency in the network data model. in RDF, all data is modeled as binary relations, and thus all data is "in the graph". thus, all data in an RDF model is at once amenable to the kind of rigorous mathematical analysis and logical inference that the relational model is, and also mappable to a graph (a labeled directed graph, to be more exact). add to that basic structure a self-describing format, and the result is a model of data that achieves an elegance, simplicity, and flexibility that Bachman's model never did, making it a beautiful fit for the web.
Chamberlin: Well, you know I've thought about it, and I think the world needs a new query language every 25 years. Seriously, it's very gratifying to be able to go through two of these cycles. DB2 will support SQL and XQuery as sort of co-equals, and that's the right approach. It embodies the information integration idea that we are trying to accomplish.
Haderle: And do you think that, given the Internet's predominantly pointer-based navigation, that Charles Bachman [originator of the network database model] is thinking, "I finally won out over relational?"
Chamberlin: Well, there are a lot of hyperlinks in the world, aren't there? I have a talk, "A Brief History of Data," that I often give at universities. And in this talk, I refer to the Web as "Bachman's Revenge."
Haderle: I know that the IMS guys are saying, "I told you so."
in much the same way that the strength of RDF as a universal data model seems to be a result of it being a simplification and distillation of the essence of other models of data, with more dynamism and flexibility, the success of Java was driven in its early days by it being in some sense a distillation of the essence of other popular programming languages and platforms, that was simpler than any of the existing programming languages and platforms - a lowest common denominator that held the promise of portability across all platforms.
Back to the basics ...
so what i'm advocating, in part to help clear up the noise and confusion surrounding this technology, and partly to focus resources where they would reap the most value at this yet early stage in its evolution, is a focus on a simpler RDF. i'm more interested in an RDF--, than an RDF++. the reason the web took off was because it was so simple to use. anyone could write an HTML page. the hyperlink is the most basic and intuitively graspable data structure one could imagine. RDF, in its basic form, doesn't really do much more than add a label to that link, introduce a new kind of node - a literal, and a powerful query language against this network of nodes with labeled links. RDF has yet to "take off". let's wait till that happens and it gains some real traction before we start over-engineering it. let's see how we can cope without schemas and ontologies. let's see if the self-organizing nature of the web will allow us to get away without them. then maybe we'll discover that it's possible to start integrating the world's data on a grand scale.