Semantic_Web

|Alexandria University | | | |Institute of Graduate Studies and Research | |Information Technology Department | | | | | |Web and E-commerce Technologies | |Introduction to the semantic web | | | | | | | | | | | | | | | | | | | | | | | | | | | |Fatema Samir Dawa | |December ,2009 | Table of contents 1.0 introduction 2 1.1 What is the World Wide Web' 2 1.1.0 Some important expressions 2 1.1.1 Markup language 2 1.1.2 Syntax 2 1.1.3 Semantics 2 2.0 What is the semantic web' 2 2.1 Benefits of the semantic web 3 3.0 The implementation of the semantic web 3 3.1 XML and the semantic web 4 3.2 RDF and the semantic web 4 3.3 Ontologies 4 3.4 Agents 5 4.0 Evolution of Knowledge 6 5.0 Examples 6 5.1 projects 6 FOAF 6 SIOC 6 SIMILE 6 NextBio 6 1.0 introduction 1.1 What is the World Wide Web' World Wide Web (commonly shortened to the web) is a collection of documents linked together and stored on servers and is being accessed via the Internet with a web browser [1]. Web pages may contain text, images, videos and other multimedia and the navigation between them is done by the hyperlinks using the concepts of the earlier hypertext systems [1]. To be able to identify what is the semantic web we must be able to identify some expressions 1.1.0 Some important expressions 1.1.1 Markup language It is an artificial language in which the web pages are composed [2] 1.1.2 Syntax It is the rules and principles that govern the sentence structure of a language; it is how you say something [3]. 1.1.3 Semantics It is the study of meaning in communication, it is what the sentence actually means [4]. Syntax and semantics are related, when we talk about syntax and semantics we are talking about the communications between computers, the Internet is designed to enable computers to talk to one another but it is not designed to teach them what the data actually means .To retrieve and deal with data we use the Markup language like HTML (hyper text markup language).HTML defines the syntax that computers can understand, it tells the computer how to display the data for us. 2.0 What is the semantic web' The semantic web is the evolution of a Web that consisted largely of documents for humans to read to one that included data and information for computers to manipulate. The Semantic Web is a Web of actionable information. It is an extension of the World Wide Web in which the semantics of information and on the web is defined, making it possible for the web to understand and satisfy the requests of people and machines to use the web content [5][8]. To express the meaning more clearly we might give an example of a semantic web: Imagine that you need to take your mother to a doctor twice a week and you need to decide which clinic depending on your working hours and the insurance and the prescribed treatment. Now imagine that you are able to use Semantic Web agent through a handheld Web browser which can retrieve information about your prescribed treatment from the doctor's agent, then look up several lists of providers, and check for the ones in-plan for your mother's insurance within a 20-mile radius of her home and with a rating of excellent or very good on trusted rating services. Then begin trying to find a match between available appointment times (supplied by the agents of individual providers through their Web sites) and your busy schedules. And then in a few minutes the agent presents you a plan and if you didn't like the plan you can redo the search with stricter preferences [5][8]. 2.1 Benefits of the semantic web 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. Enabling computers and people to work in cooperation. The first steps in weaving the Semantic Web into the structure of the existing Web are already under way. In the near future, these developments will be the start of significant new functionality as machines become much better able to process and "understand" the data that they just display at present [5][8]. 3.0 The implementation of the semantic web We have the Internet that makes us talk to each other, we have the web that enables us to store and retrieve any document and we have the search engines which can find us any web site that we want. How we can make the web any better' The answer is the semantics, computers blindly retrieve and show us information and that’s the problem while they understands the syntax the semantics are lost on them ,now if we can get computers to recognize what is in a web page they could learn what we are interested in, and if they know that they can help us to get what we want. They would change from passively helping us to actively helping us. So while the web is about documents the semantic web is about things (people, places, events, music, movies...) .Semantic web is not only about pointing these things out to a computer it's more about letting computers know how are these things related to each other. There are several promising technologies that are in use today that can embed semantic web to HTML documents, the most popular technologies for developing the semantic web which are already in place: Extensible Markup Language (XML) and the Resource Description Framework (RDF)[5][8]. [pic] 3.1 XML and the semantic web XML lets everyone create their own tags, hidden labels such as or that annotate Web pages or sections of text on a page. Scripts, or programs, can make use of these tags in sophisticated ways, but the script writer has to know what the page writer uses each tag for. In short, XML allows users to add arbitrary structure to their documents but says nothing about what the structures mean. The Semantic Web will enable machines to comprehend semantic documents and data, not human speech and writings [5][6]. 3.2 RDF and the semantic web Meaning is expressed by RDF, which encodes it in sets of triples, each triple being rather like the subject, verb and object of an elementary sentence. These triples can be written using XML tags. In RDF, a document makes assertions that particular things (people, Web pages or whatever) have properties (such as "is a sister of," "is the author of") with certain values (another person, another Web page). This structure turns out to be a natural way to describe the vast majority of the data processed by machines. Subject and object are each identified by a Universal Resource Identifier (URI), just as used in a link on a Web page. (URLs, Uniform Resource Locators, are the most common type of URI.) The verbs are also identified by URIs, which enables anyone to define a new concept, a new verb, just by defining a URI for it somewhere on the Web [3]. The triples of RDF form webs of information about related things. Because RDF uses URIs to encode this information in a document, the URIs ensure that concepts are not just words in a document but are tied to a unique definition that everyone can find on the Web. For example, imagine that we have access to a variety of databases with information about people, including their addresses. If we want to find people living in a specific zip code, we need to know which fields in each database represent names and which represent zip codes. RDF can specify that "(field 5 in database A) (is a field of type) (zip code)," using URIs rather than phrases for each term [5][7]. 3.3 Ontologies What if two databases may use different identifiers for what is in fact the same concept, such as zip code. A program that wants to compare or combine information across the two databases has to know that these two terms are being used to mean the same thing. Ideally, the program must have a way to discover such common meanings for whatever databases it encounters. A solution to this problem is provided by the third basic component of the Semantic Web, collections of information called ontologies. In philosophy, an 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 And for them an ontology is a document or file that formally defines the relations among terms. The most typical kind of ontology for the Web has a taxonomy and a set of inference rules. The taxonomy defines classes of objects and relations among them. For example, an address may be defined as a type of location, and city codes may be defined to apply only to locations, and so on. Classes, subclasses and relations among entities are a very powerful tool for Web use. We can express a large number of relations among entities by assigning properties to classes and allowing subclasses to inherit such properties. If city codes must be of type city and cities generally have Web sites, we can discuss the Web site associated with a city code even if no database links a city code directly to a Web site. Inference rules in ontologies supply further power. An ontology may express the rule "If a city code is associated with a state code, and an address uses that city code, then that address has the associated state code." A program could then readily deduce, for instance, that a Cornell University address, being in Ithaca, must be in New York State, which is in the U.S., and therefore should be formatted to U.S. standards. The computer doesn't truly "understand" any of this information, but it can now manipulate the terms much more effectively in ways that are useful and meaningful to the human user [5][8]. 3.4 Agents The real power of the Semantic Web will be realized when people create many programs that collect Web content from diverse sources, process the information and exchange the results with other programs. The effectiveness of such software agents will increase exponentially as more machine-readable Web content and automated services (including other agents) become available. The Semantic Web promotes this synergy: even agents that were not expressly designed to work together can transfer data among themselves when the data come with semantics. An important facet of agents' functioning will be the exchange of "proofs" written in the Semantic Web's unifying language (the language that expresses logical inferences made using rules and information such as those specified by ontologies). For example, you have contact information whom has been located by an online service, and to your great surprise it places that contact in your town . Naturally, you want to check this, so your computer asks the service for a proof of its answer, which it promptly provides by translating its internal reasoning into the Semantic Web's unifying language. An inference engine in your computer readily verifies that this matches the one you were seeking, and it can show you the relevant Web pages if you still have doubts. Although they are still far from plumbing the depths of the Semantic Web's potential, some programs can already exchange proofs in this way, using the current preliminary versions of the unifying language. In the next step, the Semantic Web will break out of the virtual realm and extend into our physical world. URIs can point to anything, including physical entities, which means we can use the RDF language to describe devices such as cell phones and TVs. Such devices can advertise their functionality what they can do and how they are controlled much like software agents. Being much more flexible than low-level schemes such as Universal Plug and Play, such a semantic approach opens up a world of exciting possibilities [5][8]. We could say that the Semantic Web can assist the evolution of human knowledge as a whole. 4.0 Evolution of Knowledge The semantic web is not only the tool for conducting individual tasks that we have discussed so far. In addition, if properly designed, the Semantic Web can assist the evolution of human knowledge as a whole. The Semantic Web, in naming every concept simply by a URI, lets anyone express new concepts that they invent with minimal effort. Its unifying logical language will enable these concepts to be progressively linked into a universal Web. This structure will open up the knowledge and workings of humankind to meaningful analysis by software agents, providing a new class of tools by which we can live, work and learn together [5][8] . 5.0 Examples 5.1 projects FOAF A popular application of the semantic web is Friend of a Friend (or FoaF), which describes relationships among people and other agents in terms of RDF [8]. SIOC The SIOC Project - Semantically-Interlinked Online Communities provides a vocabulary of terms and relationships that model web data spaces. Examples of such data spaces include, among others: discussion forums, weblogs, blogrolls / feed subscriptions, mailing lists, shared bookmarks, image galleries [8]. SIMILE Semantic Interoperability of Metadata and Information in unlike Environments SIMILE is a joint project, conducted by the MIT Libraries and MIT CSAIL, which seeks to enhance interoperability among digital assets, schemata/vocabularies/ontologies, meta data, and services [8]. NextBio A database consolidating high-throughput life sciences experimental data tagged and connected via biomedical ontologies. Nextbio is accessible via a search engine interface. Researchers can contribute their findings for incorporation to the database. The database currently supports gene or protein expression data and is steadily expanding to support other biological data types [8]. Reference [1] Wikipedia.org . "The world wide web." Available at: http://en.wikipedia.org/wiki/World_Wide_Web. [2] Wikipedia.org. "Markup language". Available at: http://en.wikipedia.org/wiki/Markup_language. [3] Wikipedia.org ."Syntax" . Available at: http://en.wikipedia.org/wiki/Syntax [4] ] Wikipedia.org ."Semantics" . Available at: http://en.wikipedia.org/wiki/Semantics [5] www.sciam.com . Scientific American magazine. "The semantic web". Available at: http://www.sciam.com/article.cfm'id=the-semantic-web&print=true. [6] www.w3schools.com ."XML Introduction" . Available at: http://www.w3schools.com/xml/xml_whatis.asp . [7] www.w3schools.com . "RDF Introduction" . Available at : http://www.w3schools.com/rdf/default.asp . [8] wikipedia.org/wiki/Semantic_web . "Semantic Web" . Available at : http://en.wikipedia.org/wiki/Semantic_web .