What is the Semantic Web?

What is the Semantic Web? The Semantic Web is the name of a long-term project started by W3C with the stated purpose of realizing the idea of having data on the Web defined and linked in a way that it can be used by machines not just for display purposes, but for automation, integration, and reuse of data across various applications (from the W3C Semantic Web Activity Statement). The Semantic Web is a Web technology that lives on top of the existing Web by including machine -readable information in files without modifying the existing Web structure.

In its current format, raw HTML text and images contain meta--information that is readily understandable by a human, but has little or no meaning to computer programs. For instance, popular search engines can help you locate files containing specific wards, but this content may not actually be what you're looking for. If the content matches the words you searched on, but pertains to a different topic than you had in mind, the result will not be what you intended There is also no way for the search engine to relate to other related content a few steps down the virtual relationship path. The characters 95495 could mean a dryer belt, an American postal code, a street address, or a set of dinosaur slipper socks Human language can efficiently operate when using the same term to mean somewhat different things, but automation does not.

In another example, let's say you were doing research on a CEO named Attilio Russo (fictitious), A standard HTML search will took for string occurrences (along with some fuzzy logic to find parts! matches, etc.) of documents that contain Attilio Russo. In a semantic Web model, there would be semantic searches that look for documents on the Web with relationships to that data, that would then compile and organise the relationships and give you things like a list of previous companies Attilio worked for the board of directors of those companies, companies those board members worked for, etc. This would allow a computer to form relationships from data on the Web in a way in which only humans can do currently.

The Semantic Web is designed to allow reasoning and inference capabilities to be added to the pure descriptions. In its simplest form, this includes stating facts such as "a hex-head bolt is a type of machine bolt." but extends to the formation of complicated relationships. Features like this allow Intelligent software to act on this descriptive information and follow logic paths based on them.

The two most important technologies for developing the Semantic Web are eXtensible Markup Language and the Resource Description Framework. XML allows content creators to label information in a meaningful way (i.e., <Dryer><Part>95405 </Part></Dryer>). Programs can make use of these tags in sophisticated ways, but the program has to know what the content creator uses each tag for. In summary. XML allows users to add arbitrary structure to their documents but says nothing about what the structures mean.

RDF expresses the meaning of XML. The W3C developed this new logical language to facilitate interoperability of applications which generate and process machine -understand able representations of data resources on the Web. In RDF, a document makes assertions that particular things have properties (such as "is a brother of. "Is the CEO of) with certain values. This structure turns out to be a natural way to describe the majority of data processed by machines. Within this structure, the subject and object are each identified by a Universal Resource Identifier, similar to the concept of a link on a Web page. URLs are the most common type ol URI.

Even with the above framework in place, two databases may use different identifiers for what is in fact the same concept. A program that wants to compare or combine information across the two databases has to know that these two terms mean the same thing. The program must have a way to discover such common meanings for whatever databases it encounters.

Ontologies provide (he solution to this problem. In philosophy, ontology is a theory about the nature of existence, of what types of things exist; ontology as a discipline studies such theories. Artificial-intelligence and Web researchers have co-opted the term for their own jargon, and for them the term ontology refers to a document or file that formally defines the relations among terms. The Semantic Web will advance the relational database model and overturn old ways of organizing information, according to Berners-Lee. Rather than listing information in tree structures, it will create a Web based on the relationships of people, places and things as they exist in the real world.

He expressed the belief that Semantic Web technology will advance the information revolution he began with the World Wide Web, changing everything from how users set up their online address books to how they pay their taxes.

Do we need the Semantic Web?

Paul Festa

Is the "Semantic Web" the new Internet, or just a complex technology in search of a problem to solve? Attempting to quell widespread scepticism, standards advocates say recent implementations of Semantic Web protocols by large technology companies herald the arrival of the Internet's next evolutionary phase.

Backers of the technology--led by W3C director Tim Bemers-Lae an Englishman who was knighted for his creation of the Web's first protocols--make big claims for it, comparing its advent to the dawn of the Web 10 years ago. Just as the Web encompassed existing Internet technologies while adding its revolutionary system of hyperlinks, so, they claim, will the Semantic Web give birth to vastly more powerful ways of gleaning information from the world's computer network.

Such claims are being measured against concerns about personal privacy and technological complexity, and against perceptions that the Semantic Web activity is pie-in-the-sky artificial intelligence research that;s distracting the consortium from its mission of maintaining fundamental "good enough" Web protocols. What's more, some analysts and technologists who follow the WSC's work closely say that even after years of work and the publication of several foundational documents, they still have no idea what the Semantic Web is.

"I'm not against any attempts to do more sophisticated knowledge management on the Web," said Peter O'Kelly, an analyst with the Burton Group. "But if s not entirely clear to me what problem these guys think they're solving. The simplicity and robustness of the Web we have today is one of the things that's made it so successful. The Semantic Web is not going to be as broadly applicable as the technologies we have today. With all due respect to Sir Tim, there's a lot of mileage left in the Web as we know it." Bemers-Lee said in an interview that the haze of confusion surrounding the Semantic Web activity has a familiar ring. "If s akin to the responses I got years ago when I was trying to explain this Web thing to people, especially in industry," Bemers-Lee said. "The idea of a universal information space with identifiers and one-way links was a paradigm shift. We didn't have the vocabulary then to describe the things we take for granted now with regards to the Web in general. So it is with the Semantic Web."

Selling the concept

This week's conference is intended, in part, to familiarise people with the vocabulary of the Semantic Web and sell a business-oriented audience on the idea that applications of the protocols are not only possible, but are already in use by companies including Adobe Systems, HP, IBM, Nokia and Oracle.

Panels at the conference range from "The Semantic Broker as e-Commerce Enabler" to "Ontological Semantic Cognitive Data Measurement and Business Intelligence". Enterprise and government case studies also will be presented.

The Semantic Web protocols aim to let computers distinguish different kinds of data. Armed with those distinctions, applications could more automatically trade information, for example between an online address book and a mobile phone. A Web site could automatically reconfigure itself on the fly based on the needs of a particular visitor. Search engines could narrow down results with greater precision.

"This is about connecting the data to its definition and context," Eric Miller, Semantic Web activity lead for the W3C, said in a Tuesday keynote address to several hundred conference participants. "We're moving from a Web of documents to a Web of data.

The W3C acknowledges that existing technologies already satisfy some of the needs the Semantic Web is designed to fill. One is the consortium's XML recommendation for creating highly descriptive and computer-friendly markup languages. Others have to do with rapidly evolving database management systems.

But Berners-Lee and others developing the new technology envision a comprehensive shift in the way data is exposed to the Web.

"When a large enterprise designs lots of database schemes and XML schemes, the designers are making arbitrary design choices about exactly how to build the system," Berners-Lee said.

"These choices have no actual connection to the real application, yet they are baked into the system," he added. "Anyone who uses the data has to know what these decisions are."

Key goals for the Semantic Web architects include reuse of data and what backers call "recombinant effects."

They hope that by letting computers digest and exchange information about context and meaning--a word that raises the hackles of artificial intelligence critics--they will allow data to survive the systems where it originated and traverse different applications as easily as browsers traverse the Web's billions of pages today. As that data takes on a virtual life of its own, it could be exploited and combined in unexpected and unexpectedly profitable ways, the thinking goes.

"The really exciting thing isn't that you can merge your own data between applications--that's like links on your own Web site," Berners-Lee said. "The really exciting thing happens when others have their data in a mergeable format and make it available. When that public information becomes mergeable, we're in for the next, very pronounced stage of Web evolution."

Security worries

That brave new world of interchangeable data--"exposing data hiding in documents, servers and databases," in Miller's words--elicits both scepticism and alarm from critics of the emerging project.

One concern is that businesses with a Semantic Web presence may have a new headache in trying to prevent information from being unintentionally shared.

"We don't want to have this universal network of knowledge that makes everything accessible to all parties," said the Burton Group's O'Kelly. "Companies need to be circumspect about disclosure."

The W3C, acknowledging concerns about corporate and personal privacy, says it plans a Semantic Web rules system for information sharing. The consortium is calling for position papers by 18 March for its workshop on rule languages for interoperability, set for 27-28 April in Washington DC.

Even though crucial protocols are still in the idea phase, the W3C is insisting that the Web's next big evolutionary shift has already begun.

The WSC's Miller devoted much of his keynote address--titled "The Semantic Web Is Here"--to existing examples of Semantic Web technologies being developed or rolled out by major companies.

Nokia, for example, maintains long-standing Semantic Web activity of its own and has made its Semantic Web toolkit, known as Wilbur, available on the SourceForge.net open source development site.

Miller hailed the way Nokia has used Semantic Web specifications, particularly RDF, in its Series 60 phones and in its developers' forum. In one of Miller's examples, RDF metadata, or data about data, lets phones communicate to Web sites about how much bandwidth they have. In another, RDF lets Nokia automatically serve pages individually tailored for developers of particular applications for certain phones.

Miller also cited other examples: HP's use of Semantic Web technologies In its work building an online education resource for the government of Singapore; the IBM Internet Technology Group's development of Semantic Web applications, especially those in the life sciences; Adobe's addition of RDF-based XMP (Extensible Metadata Platform) in its Creative Suite, which Adobe says sits on more than 700,000 computers; and Oracle's inclusion of the RDF Network Data Model in its Oracle Database 10.2, due out later in the year.

Also during his keynote, Miller laid out plans to spread the Semantic Web religion. He said he plans to ask the W3C membership to endorse a working group devoted to Semantic Web education and communication, and he also plans a Semantic Web symposium for CTOs and C1Os June 22-24 at a yet-to-be-determined West Coast location.

After years of being called artificial-intelligence throwbacks with their heads in the clouds, Semantic Web backers point to these real-world implementations with evident satisfaction.

"The Semantic Web is starting to take off now" Berners-Lee said. "It is not yet so developed that [implementers] keep bumping into people doing related things yet--we are not yet really seeing the benefit of application areas being connected together in unexpected ways. But in certain areas, the critical mass has been passed. At the recent Semantic Web and life sciences workshop ... there was serious excitement about the opportunities in integrating across life science disciplines, like genomics, proteomics, clinical trial and epidemiological data and so on."

Potential Benefits of The Semantic Web

Humans are capable of using the Web to, say, find the Swedish word for "car", renew a library book, or find the cheapest DVD and buy it. But if you asked a computer to do the same thing, it wouldn't know where to start. That is because web pages are designed to be read by people, not machines. The Semantic Web is a project aimed to make web pages understandable by computers, so that they can search websites and perform actions in a standardized way. The potential benefits are that computers can harness the enormous network of information and services on the Web. Your computer could, for example, automatically find the nearest manicurist to where you live and book an appointment for you that fits in with your schedule.

A lot of the things that could be done with the Semantic Web could also be done without it, and indeed already are done in some cases. But the Semantic Web provides a standard which makes such services far easier to implement.

Relationship to the World Wide Web

Currently, the World Wide Web is based primarily on documents written in Hyper Text Markup Language (HTML), a language that is useful for describing, with an emphasis on visual presentation, a body of structured text interspersed with multimedia objects such as images and interactive forms. HTML has limited ability to classify the blocks of text on a page, apart from the roles they play in a typical document's organization and in the desired visual layout.

For example, with HTML and a tool to render it (perhaps Web browser software, perhaps another user agent), one can create and present a page that lists items for sale. The HTML of this catalog page can make simple, document-level assertions such as "this document's title is Widget Superstore'". But there is no capability within the HTML itself to unambiguously assert that, say, item number X586172 is an Acme Gizmo with a retail price of 199 [euro], or that it is a consumer product. Rather, HTML can only say that the span of text "X586172" is something that should be positioned near "Acme Gizmo" and "199 [euro]", etc. There is no way to say "this is a catalog" or even to establish that "Acme Gizmo" is a kind of title or that "199 [euro]" is a price. There is also no way to express that these pieces of information are bound together in describing a discrete item, distinct from other items perhaps listed on the page.

The Semantic Web addresses this shortcoming, using the descriptive technologies Resource Description Framework (RDF) and Web Ontology Language (OWL), and the data-centric, customizable Extensible Markup Language (XML), These technologies are combined in order to provide descriptions that supplement or replace the content of Web documents. Thus, content may manifest as descriptive data stored in Web-accessible databases, or as markup within documents (particularly, in Extensible HTML (XHTML) interspersed with XML, or, more often, purely in XML, with layout/rendering cues stored separately). The machine-readable descriptions enable content managers to add meaning to the content, thereby facilitating automated information gathering and research by computers.

Components of the Semantic Web

The Semantic Web is comprised of the standards and tools of XML, XML Schema, RDF, RDF Schema and OWL. The OWL Web Ontology Language Overview (http://www.w3.org/TR/owl-features/) describes the function and relationship of each of these components of the Semantic Web:

* XML provides a surface syntax for structured documents, but imposes no semantic constraints on the meaning of these documents.

* XML Schema is a language for restricting the structure of XML documents.

* RDF is a simple data model for referring to objects ("resources") and how they arc related. An RDF-based model can be represented in XML syntax.

* RDF Schema is a vocabulary for describing properties and classes of RDF resources, with a semantics for generalization-hierarchics of such properties and classes.

* OWL adds more vocabulary for describing properties and classes: among others, relations between classes (e.g. disjointncss). Cardinality (e.g. "exactly one"), equality, richer typing of properties, characteristics of properties (e.g. symmetry), and enumerated classes.

The intent is to enhance the usability and usefulness of the Web and its interconnected resources through:

* documents "marked up" with semantic information (an extension of the HTML <meta> tags used in today's Web pages to supply information for Web search engines using web crawlers). This could be machine-readable information about the human-readable content of the document (such as the creator, title, description, etc., of the document) or it could be purely metadata representing a set of facts (such as resources and services elsewhere in the site). (Note that anything that can be identified with a Uniform Resource Identifier (URI) can be described, so the semantic web can reason about people, places, ideas, cats, etc.)

* common metadata vocabularies (ontologies) and maps between vocabularies that allow document creators to know how to mark up their documents so that agents can use the information in the supplied metadata (so that Author in the sense of 'the Author of the page' won't be confused with Author in the sense of a book that is the subject of a book review).

* Automated agents to perform tasks for users of the Semantic Web using this metadata

* Web-based services (often with agents of their own) to supply information specifically to agents

Real World Computing

Davey Winder

Its generally accepted that Hanns Oertel in his 'Lectures on the study of language' in 1901 was the first to clearly distinguish between the formal and the Semantic definitions of a word-the latter relates to its significance or meaning. The Semantic Web is a mechanism for linking the contextual meaning of online data in such a way that it can be processed efficiently by a computer while remaining accessible to humans. The concept of metadata is nothing new, but Berners-Lee goes way beyond simple keyword tagging: his vision is one of a unifying logical language that can progressively link concepts old and new into a truly universal web. A structure that will 'open up the knowledge and workings of humankind to meaningful analysis by software agents'. He continued: The Semantic Web will bring structure to the meaningful content of web pages, creating an environment where software agents roaming from page to page can readily carry out sophisticated tasks for users.' This wouldn't require any great leap forward in Al, but merely that the data be published in a more informative format than today's HTML. By taking a Semantic Web approach, information literally becomes free to be used within whatever context someone requires, even if far removed from its original purpose.

RDF, FOAF, XML and other acronyms

At the heart of the Semantic Web lies the Resource Description Framework (RDF), a set of specifications based upon the idea of 'making statements about resources in the form of a subject-predicate-object expression', according to the Wikipedia. Maintained by the World Wide Web Consortium (W3C), which Berners-Lee heads, RDF provides a methodology for describing resources while retaining a relatively simple data model. Publish your information to the public domain using RDF (plus XML, which has become a de facto part of the framework, and a uniform resource identifier that identifies and links resources) and once so published it can be repurposed in any way another application or user sees fit.

Will therefore the Semantic Web make meaning understandable to computers, creating a medium for universal information exchange? Well yes, in theory. The problem is that there are very few examples out there that you can go and play with. You could take a look at the FOAF= Project (www.foaf-project.ora). which is all about creating a web of machine-friendly home pages that describe the links between people, the data they create and the things they do. Unfortunately, it seems to have lost momentum somewhat and many of its links are broken. The FOAF Explorer (http://xml.mfd-consult.dk) offers a web-based overview of the FOAF Project and may be a better starting point Then there's BigBlogZoo (www.bigblogzoo.com), which claims to be the world's first semantic web browser, but in reality bears more than a passing resemblance to a blog/newsfeed browser (that's just what it is, of course). It defines a newsfeed as being a semantic reference to a web page because it adds dates, languages, categories and descriptions to the website itself. Download it and play with yourself: you get 80,000 or so XML feeds, categorised using the DMOZ schema and all of which can be spidered according to your preferences.