There are at least two broad plans for the direction in which the Web may evolve and, significantly, each of them has XML as a keystone.
The first, known colloquially as "web services", is largely the domain of the largest corporate IT vendors, most notably Microsoft and IBM. The web services movement is often criticized by its detractors for having, in the end, very little to do with the Web, a criticism most recently levied in these pages by Edd Dumbill's essay, "Kicking Out the Cuckoo".
The second, the "Semantic Web", is largely the domain of the W3C, academic, government, and some industry researchers. Curiously, the W3C seems to have taken the position that the Semantic Web, or something very much like it, is inevitable, if the Web is to mature fully: "For the Web to reach its full potential, it must evolve into a Semantic Web, providing a universally accessible platform that allows data to be shared and processed by automated tools as well as by people" (Semantic Web Activity Statement). The Semantic Web is most often criticized by its detractors for having, in the end, very little to do with reality; or, put less pointedly, for being easier to dream about than to implement. Mike Champion suggested recently that the "conventional wisdom" criticizes the W3C's Semantic Web efforts along three grounds: first, that achieving web services interoperability has a higher priority for W3C member corporations than Semantic Web efforts; second, that Semantic Web efforts have not shown yet sufficient practical fruit; third, that the Semantic Web as a technological program is unlikely to ever live up to its promise.
In what follows I introduce one of the major elements of the W3C's Semantic Web initiative, the Web Ontology Working Group (hereafter, "WebOnt"), explaining its goals, deliverables, and progress to date.
What is WebOnt Supposed to Do?
In short, WebOnt, co-chaired by Professor Jim Hendler (of University of Maryland) and Professor Guus Schreiber (of University of Amsterdam), has been given the task of developing an ontology vocabulary for use in the Semantic Web (which is to be distinguished from an ontology of the Web, i.e., a formal schema of what there is on the Web: hosts, resources, media types, and the like). This ontology vocabulary or ontology language corresponds to the foundational stratum of Tim Berners-Lee's Web Architecture layer cake diagram. But what is an ontology vocabulary? It is a formal schema (in this sense, having little to do with W3C XML Schema) which, as the WebOnt Charter puts it, allows for the "explicit representation of term vocabularies and the relationships between entities in these vocabularies".
Less formally, an ontology language is a markup language -- presumably in XML, but RDF is possible, too -- that allows users to define formal ontologies or schemas (a perfectly unobjectionable synonym of "ontology" before the W3C again co-opted a very generic term for a very specific standard) for particular problem domains. WebOnt is not going to deliver ontologies for particular problem domains; rather, WebOnt intends to create the standardized markup language within which users can formally define specific ontologies for use on the Web. The important point to come to terms with is, whether DAML+OIL or WebOnt or some other project, if Web-scale interoperability is going to be achieved in the area of knowledge representation -- an achievement that the Semantic Web absolutely presupposes -- there needs to be one, preferably well-engineered way to declare and define formal schemas, such that tools which function at Web-scale can be easily implemented and deployed.
WebOnt's ontology language will make it possible to represent, in a machine-readable form, assertions about class and property relationships between logical entities, as well provide a "means to limit the properties of classes with respect to number and type, means to infer that items with various properties are members of a particular class, [as well as] a well-defined model of property inheritance" (WebOnt Charter).
In even shorter, more mundane form, WebOnt is tasked with cleaning up and otherwise standardizing the DAML+OIL ontology language, which was submitted to the W3C as a NOTE in late 2001, and which in turn came out of the DARPA Agent Markup Language and the Ontology Inference Layer projects.
WebOnt Requirements
One of the first substantive work products to come out of WebOnt thus far is a Working Draft, "Requirements for a Web Ontology Language", which makes for rather interesting reading, including use cases, design goals, requirements, and objectives.
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Among the use cases for a Web Ontology language, the Requirements WD lists web portals, multimedia collections, corporate web site management, design documentation, intelligent agents, and ubiquitous computing. A web portal, for example, could use a formal ontology covering the knowledge domain the portal focuses on; for example, medical research about the origin of AIDS. In order to collect, analyze, share, and structure information, it would be helpful if the portal had a public ontology available for its own use and the use of its information-sharing partners, including medical publishers, university researchers, health organizations, and the like. An appropriately-encoded and rigorous ontology "can provide an expressive terminology for describing content, and inferences sanctioned by the ontology can be used to improve the quality of search on the portal" (WebOnt Requirements WD). In the use case of intelligent agents, to take another common example, an ontology can be useful in order to allow software constructs to manipulate and make inferences about knowledge (as opposed to mere data) it retrieves from various Web resources.
The WebOnt Requirements WD also lists eight design goals of a Web Ontology language. The first is that it should provide for ontology sharing, including the ability of one public ontology to extend another public ontology by, perhaps, specializing some of its terms or properties.
The second design goal is to support the change or drift over time of ontologies and their constitutive parts. As knowledge domains evolve, ontologies must be able to evolve in order to continue to formally represent their domain. Revisions and versions of ontologies must be supported by the underlying ontology language.
Third, a web ontology language must support interoperability, which means that it must offer some way to map similarities between disparate ontologies, at least insofar as two ontologies which ostensibly formalize the same problem domain have significant conceptual similarities. It is important to note, however, that adding mapping primitives to the standard web ontology language will never of itself be sufficient to achieve interoperability across any particularly instance of disparate, competing ontologies. It may be the case that no such interoperability is possible; that is, there is little, if any theoretical assurance that any two competing ontologies are practically reconcilable. (For an argument which addresses the issue of competing schemas, see "The Politics of Schemas", a two-part XML.com article series from early 2001.)
The fourth design goal -- which seems presently underspecified and vague, in my view -- says that "Different ontologies or data sources may be contradictory. It should be possible to detect these inconsistencies". It does not, however, specify what kind of inconsistency -- logical, factual, or some other? -- should be detectable, or whether the fact of a kind of inconsistency is to be part of a resolved ontology, which seems to be the implication of noting that "RDF and RDFS do not allow inconsistencies to be expressed". It is not very clear, then, whether this design goal is about the detection of some kind of inconsistency among ontologies (or data sources? Or both?) or whether it is also about the inclusion in a web ontology language of some way to represent some kind of inconsistency in an ontology.
Fifth, a web ontology language should strike a balance between, on the one hand, expressiveness of knowledge representation and, on the other, scalability of the processing or reasoning model.
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The sixth design goal is that a web ontology language should be easy to use, and both syntax and semantics are mentioned. There is some implication that more human-friendly syntax might be warranted.
Seventh, a web ontology language should be serializable in XML.
Eighth, a web ontology language must pay due attention to the formally global character of the Web, which, one may dare to hope, will mean more than simply falling back on the claim that XML is Unicode and internationalization-friendly.
Conclusions
So far, so good. There have been unexpected benefits due to the increased attention being paid, by the members of WebOnt and by many others under the auspices of the Semantic Web Coordinating Group, to relevant existing W3C standards, particularly RDF and RDF Schema. Problems and unresolved questions have been identified which must be addressed if the work of WebOnt is to be move forward and prosper.
If the Semantic Web is worth pursuing at all, something like a W3C-blessed Web Ontology Language is not only desirable but necessary. Though I lament yet another W3C generically named specification as unhelpful and confusing, the WebOnt WG which has been assembled to produce this crucial element of the Semantic Web is so far proving to be determined and capable. But only time will tell.
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Comment on this Article
| Titles Only | Full Threads | Newest First |
- Ontology Language ...
2002-12-20 21:48:53 Bernard (Ben) Tremblay [Reply]
It seems to me that some very lofty ideas are nearly come to earth. I'm happy to find snippets like this (quoted in David Steinberg's comment to "Kicking out the Cukoo")
from Web Service Description Requirements -
W3C Working Draft 29 April 2002
section 4 requirements
4.12 Mapping to the Semantic Web
R070 "The WG specification(s) MUST allow
providing a mapping from the description
language to [RDF].
This, I hope, justifies using "foundational" in the following:
"This ontology vocabulary or ontology
language corresponds to the foundational
stratum of Tim Berners-Lee's Web
Architecture layer cake diagram [...] a
formal schema [...] allows for the "explicit
representation of term vocabularies and the
relationships between entities in these
vocabularies".
- Web ontology forum?
2002-06-09 06:02:00 Anonymous Anonymous [Reply]
How do I access the web ontology forum?
- Language and Communication: The Fallicy of Exclusion between the Semantic Web and Web Services
2002-05-10 04:44:26 Pierre Johnson [Reply]
Language possesses combinatorial structure, i.e., a grammar of compositional symbols for the construction composite signals, i.e., messages. Messages encapsulate the ideas entities formulate regarding phenomena they perceive. Language enables entities to associate a temporal quality with their ideas. This temporal quality is a description of past events, instant events, and potential, future events; with ideas.
Language facilitates complex, continuous, asynchronous communication of ideas that coordinate action among entities involved within an activity. Language permits any given entity to function simultaneously as a sender and receiver of messages.
If one understands the theoretical development of language, one understands that the concurrent development of web services and the semantic web are not diametrically opposing concepts that threaten the survival of each other. Theoretically, language began with hominid humans. Linguists refer to this language as a proto-language that consisted of vocabulary grunted by its speakers as one or two word phrases, e.g., mom hungry, hungry mom, where both phrases mean the same thing.
All known XML schemas, i.e., vocabularies are this proto-language. This proto-language constitutes the semantic web.
For a proto-language to become an expressive language, i.e., one that facilitates complex, continuous, asynchronous communication of ideas, the rise of syntax must occur. Syntax is the collection of rules that govern the structure of a language statement. Syntax specifies how compositional symbols combine to form phrases that intend to impart significant ideas.
Element tags of any given XML instance are nothing more than nouns and their associated descriptions. Web services represent verbs of language, words that explain action. When XML combines with applications that process XML, i.e., web services, we acquire a language for the communication of complex ideas.
Users of spoken compositional languages can construct an unlimited amount of complex, information-bearing expressions derived from a relatively small amount of basic symbols. The channel of speaking compositional languages is simple and non-proprietary in nature. No single person owns a language. There isn’t a proprietary format that encodes our language.
The HTTP protocol is the appropriate channel that carries our new language for the same reason. Other protocols work suitably well for the transmission of messages encoded within a proprietary format. HTTP allows non-proprietary encoded compositional symbols to flow freely from sender to receiver. ASCII and Unicode files are easy to encode and no one earns a royalty from their use. A XML file served to a client through HTTP is a perfect example of this simplicity.
The web services vs. semantic web war is not unlike a dreaded nuclear war becoming real for everyone on earth because individuals signed away their property rights to allegedly representative, democratic governments. Neither the W3C, which represents the semantic web camp, nor select corporations, which represent the web services camp, have our best interests within their minds. The time has come to liberate ourselves from dictatorial decrees forced upon us by these entities. Internet and WWW standards should come from an open source model.
I encourage each of you to read my article regarding this debate. One can find my article from a link that exists on the web page written by Mr. Dumbill regarding this issue.
- Epistemology and Ontology: Helping the folks at the Web Ontology Working Group
2002-05-10 02:07:19 Pierre Johnson [Reply]
Epistemology is the philosophical theory of knowledge, i.e., the study of knowledge. Ontology is the theory of the nature of being and existence, i.e., the study of the nature of being and existence. We create epistemological theories to support the ontological theories that we create.
My provisioning of these definitions clarifies the exact problem facing the folks at the Ontology Working Group of the W3C, whether or not they realize this distinction between the two concepts. When abstracted to its highest level, knowledge amounts to a classification system, a dictionary of entries and descriptions, which represents one instance of our perception of the nature of being and existence, i.e., a mythology. Developing an epistemology that is closer to perfection allows us to develop an ontology that is closer to perfection.
The entries within this epistemological dictionary possess a temporal number line quality whose origin represents this instant of time, whose past events occur to the left of the origin and whose expected future event occur to the right of the origin. The set of entries that might exist to the right of the origin represent possible futures, i.e., possible past events or what we call knowledge.
Correctly, the folks at the OWG of the W3C must want to create a epistemological philosophy that allows people to abstract their respective knowledge domains at any given instant in time, i.e., frame of reference. Presumably, the OWG folks must want to use an agreed upon, well-defined XML lexicon, i.e., vocabulary and syntax, as the model of knowledge abstraction.
Again, presuming these assumptions are correct, this model will allow any given set of humans to share knowledge through their proxies of human-purposed applications and machine-purposed applications.
Current knowledge representations using XML resemble proto-languages. These proto-languages consist of morphemes, i.e., element types grunted within a syncopated rhythm. Presumably, early hominid humans spoke proto-languages. To become an expressive language, any given language requires a vocabulary and syntax, i.e., a canonical ordering of words that represent various parts of speech. If this is the goal of the OWG, then the OWG must impose a correct partitioning of element types and the OWG must impose definitions for entries within various knowledge domains.
If the OWG of the W3C desires to map one knowledge domain against another knowledge domain, the OWG should employ the tools created by some other working groups of the W3C for exact purpose of knowledge domain transmutation. XSLT and XPath are these tools.
Simply, one should inform the OWG membership that everything existing within the universe is an object, whether or not the existence of everything is within the mind of someone, within all of our minds, collectively, or within none of our minds. If everything is an object, then one can agree to abstract knowledge according to a particular vocabulary. If one desires to create an expressive language with this vocabulary, one need create syntax.
When considering objects, one must consider the descriptive qualities that determine the intrinsic nature of an object and the descriptive qualities that determine the extrinsic nature of an object. In other words, what is the essence of something and how do we perceive it. We can define the extrinsic qualities of an object, i.e., how we perceive an object by placing the object into a set of objects.
Proposed are XML fragments that might achieve the aims of the OWG of the W3C:
<object>
<features>
<feature> value </feature>
</features>
<behaviors>
<behavior> value </behavior >
</behavior>
</object>
<object_set>
<object>
<space-time-location>
<axis>
<value> value </value>
</axis>
</space-time-location>
</object>
</object_set>
We classify objects by encapsulating them into space-time fuzzy sets, by choosing random points of centrality within randomly selected frames of reference within these sets, and by differentiating between points of centrality and our object of focus. This fundamental process assumes various names that include the ordinal, cardinal, motive, structural, causal, and mutable nature of our object.
Ultimately, an object set is an object existing in disguise. An object of an object set is a feature of that object set. Stated another way, the most abstract statement expressed using XML that captures the goals of the OWG of the W3C is simply, a dictionary entry and its corresponding description (see below). The dictionary itself is nothing more than an object that can be as simple as a web page with its corresponding reference, the data structure that supports the web page or the entire World Wide Web.
<object>
<feature>value</feature>
</object>
- Ontology
2002-05-06 12:53:40 Jeff Lowery [Reply]
As far as I understand it, an ontology infers constraints based on the relation-types between entities. For example, say we have the follow two
statements:
Joe must read the paper.
Joe must dispose of the paper.
Joe and paper are entities, read and dispose of are relational types.
If we dictate that Joe must perform both actions, we can infer a sequence of actions by understanding the relationships between Joe and paper. If we know from our ontology that disposal of reading material negates the ability to read the material afterwards, we know that in order for Joe to meet the first commitment (must read), it has to be performed prior to his second commitment (must dispose of).
Procedural code handles this as well, by explicitly stating the order of precendence of an operation. The above two statements, though, are just asserting two relational conditions between entities, not a sequence of operation. However, by having an ontological understanding of the relation "read" and "dispose of", we can infer the order of operation.
- Problems in search of a solution...
2002-05-06 09:10:33 Edwin Wiles [Reply]
One of the critical problems in "intel" work is knowing what it is that you know. The flood of information is simply too great for any one individual to peruse it all.
It is presently hoped that an ontology language, be it RDF, DAML+OIL, or something else, can be used to describe the available information in a format that makes it easy for software to (a) find related information, and (b) allow an analyst to use software to easily find otherwise unrealized (by humans anyway) connections.
There is presently at least one project that is making extensive use of DAML+OIL. This is not "a few web pages" but a significant investment in the technology.
Yes, there is a strong military presence in the project, but presently, the military and intelligence community have the strongest urge to find some solution to the information flood.
No doubt, once the techniques are sufficiently advanced, a use in the business community will be identified.
As it is, the business community has a severe aversion to spending serious money on anything that they cannot see a ROI for within the next quarter or two. (The wonders of [a] quarterly stock reporting requirements, and [b] "I want my profit NOW" thinking by investors.)
On the other hand, mil/intel have a serious aversion to failing to note the critical information they need to perform their jobs, and ROI (in terms of cash money) is not nearly as important as succeeding in their jobs.
- Solution in search of a problem?
2002-05-04 19:08:13 murray bent [Reply]
Why should the W3C be "cleaning up and otherwise standardizing the DAML+OIL" language, as nothing much resulted from that. A few web pages were produced under contract, so what?
Why can't the W3C follow a logical transparent process of documenting requirements and refining a solution in response? Making the solution fit DAML-OIL is like Stalinist science. There are too many generals walking the corridors of W3C these days.
- so far so what
2002-05-02 01:56:34 Ian Young [Reply]
So once you have one of these ontology thingies, what exactly are you supposed to be able to do with it?
