Chapter 1A Semantic Web Primer, 2nd Edition 1-1 ΤΜΗΜΑ ΠΛΗΡΟΦΟΡΙΚΗΣ, ΑΠΘ ΜΕΤΑΠΤΥΧΙΑΚΟ ΠΡΟΓΡΑΜΜΑ ΣΠΟΥΔΩΝ Κατεύθυνση Πληροφοριακών Συστημάτων - 1ο Εξάμηνο Σημασιολογικός Ιστός lpis.csd.auth.gr/mtpx/sw ή tinyurl.com/SemanticWebAUTH Διδάσκων: Ν. Βασιλειάδης Αναπλ. Καθ. Τμ. Πληροφορικής ΑΠΘ Μάθημα: 1

Coursework 3 modeling projects (10% each) – XML (DTD, XML Schema)  XML editor – RDF / RDF Schema  Protégé – OWL  Protégé 1 “programming” project (20%) – XSLT (XML presentation in HTML)  XML editor – (alternatively) linked data & SPARQL related project 1 bonus project in rules (SWRL) (5%) Exams (50%) – (alternatively) Full programming project  Java? 1-2

Chapter 1A Semantic Web Primer, 2nd Edition 1-3 Chapter 1 The Semantic Web Vision Grigoris Antoniou Frank van Harmelen

Chapter 1A Semantic Web Primer, 2nd Edition 1-4 Lecture Outline 1. Today’s Web 2. The Semantic Web Impact 3. Semantic Web Technologies 4. A Layered Approach 5. The Semantic Web Today

Chapter 1A Semantic Web Primer, 2nd Edition 1-5 Today’s Web Most of today’s Web content is suitable for human consumption – Even Web content that is generated automatically from databases is usually presented without the original structural information found in databases Typical Web uses – seeking and making use of information, searching for and getting in touch with other people, reviewing catalogs of online stores, ordering products by filling out forms

Chapter 1A Semantic Web Primer, 2nd Edition 1-6 Keyword-Based Search Engines Current Web activities are not particularly well supported by software tools – Except for keyword-based search engines (e.g. Google, AltaVista, Yahoo) The Web would not have been the huge success it was, were it not for search engines

Chapter 1A Semantic Web Primer, 2nd Edition 1-7 Problems of Keyword-Based Search Engines High recall, low precision. Low or no recall Results are highly sensitive to vocabulary Results are single Web pages Human involvement is necessary to interpret and combine results Results of Web searches are not readily accessible by other software tools

Chapter 1A Semantic Web Primer, 2nd Edition 1-8 The Key Problem of Today’s Web The meaning of Web content is not machine- accessible: lack of semantics It is simply difficult to distinguish the meaning between these two sentences: I am a professor of computer science. I am a professor of computer science, you may think. Well,...

Chapter 1A Semantic Web Primer, 2nd Edition 1-9 The Text Processing Approach Use the content as it is represented today Develop increasingly sophisticated techniques based on ΑΙ and computational linguistics. Ηas been followed for some time now – Despite some advances the task is too ambitious.

Chapter 1A Semantic Web Primer, 2nd Edition 1-10 The Semantic Web Approach Represent Web content in a form that is more easily machine-processable. Use intelligent techniques to take advantage of these representations. The Semantic Web will gradually evolve out of the existing Web – It is not a competition to the current WWW

Chapter 1A Semantic Web Primer, 2nd Edition 1-11 Semantic Web Organization Support SW is propagated by the WWW Consortium (W3C) – International standardization body for the Web. – The driving force is Tim Berners-Lee, the person who invented the WWW in the late 80s. – In his original vision of the Web the meaning of information played a far more important role than it does today. The development of the SW has a lot of industry momentum, and governments are investing heavily. – The U.S. government has established the DARPA Agent Markup Language (DAML) Project – EU’s 6th FP has the Semantic Web among the key action lines.

Chapter 1A Semantic Web Primer, 2nd Edition 1-12 Lecture Outline 1. Today’s Web 2. The Semantic Web Impact 3. Semantic Web Technologies 4. A Layered Approach 5. The Semantic Web Today

Chapter 1A Semantic Web Primer, 2nd Edition 1-13 The Semantic Web Impact – Knowledge Management Knowledge management concerns itself with acquiring, accessing, and maintaining knowledge within an organization Key activity of large businesses: internal knowledge as an intellectual asset It is particularly important for international, geographically dispersed organizations Most information is currently available in a weakly structured form (e.g. text, audio, video)

Chapter 1A Semantic Web Primer, 2nd Edition 1-14 Limitations of Current Knowledge Management Technologies Searching information – Keyword-based search engines Extracting information – human involvement necessary for browsing, retrieving, interpreting, combining Maintaining information – inconsistencies in terminology, outdated information. Viewing information – Impossible to define views on Web knowledge

Chapter 1A Semantic Web Primer, 2nd Edition 1-15 Semantic Web Enabled Knowledge Management Knowledge will be organized in conceptual spaces according to its meaning. Automated tools for maintenance and knowledge discovery Semantic query answering Query answering over several documents Defining who may view certain parts of information (even parts of documents) will be possible.

Chapter 1A Semantic Web Primer, 2nd Edition 1-16 The Semantic Web Impact – B2C Electronic Commerce A typical scenario: user visits one or several online shops, browses their offers, selects and orders products. Ideally humans would visit all, or all major online stores; but too time consuming Shopbots are a useful tool

Chapter 1A Semantic Web Primer, 2nd Edition 1-17 Limitations of Shopbots They rely on wrappers: extensive programming required Wrappers need to be reprogrammed when an online store changes its outfit Wrappers extract information based on textual analysis – Error-prone – Limited information extracted

Chapter 1A Semantic Web Primer, 2nd Edition 1-18 Semantic Web Enabled B2C Electronic Commerce Software agents that can interpret the product information and the terms of service. – Pricing and product information, delivery and privacy policies will be interpreted and compared to the user requirements. Information about the reputation of shops Sophisticated shopping agents will be able to conduct automated negotiations

Chapter 1A Semantic Web Primer, 2nd Edition 1-19 The Semantic Web Impact – B2B Electronic Commerce Greatest economic promise Currently relies mostly on EDI – Isolated technology, understood only by experts – Difficult to program and maintain, error-prone – Each B2B communication requires separate programming Web appears to be perfect infrastructure – But B2B not well supported by Web standards

Chapter 1A Semantic Web Primer, 2nd Edition 1-20 Semantic Web Enabled B2B Electronic Commerce Businesses enter partnerships without much overhead Differences in terminology will be resolved using standard abstract domain models Data will be interchanged using translation services. Auctioning, negotiations, and drafting contracts will be carried out automatically (or semi-automatically) by software agents

Chapter 1A Semantic Web Primer, 2nd Edition 1-21 Personal Agents in the Semantic Web Michael had just had a minor car accident and was feeling some neck pain. – His primary care physician suggested a series of physical therapy sessions. – He asked his Semantic Web agent to work out some possibilities.

Chapter 1A Semantic Web Primer, 2nd Edition 1-22 Personal Agents in the Semantic Web The agent: – retrieved details of the recommended therapy from the doctor’s agent – looked up the list of therapists maintained by Michael’s health insurance company – checked for those therapists located within 10 km from Michael’s office or home

Chapter 1A Semantic Web Primer, 2nd Edition 1-23 Personal Agents in the Semantic Web The agent (continued): – looked up their reputation according to trusted rating services – tried to match available appointment times with Michael’s calendar – returned two proposals

Chapter 1A Semantic Web Primer, 2nd Edition 1-24 Personal Agents in the Semantic Web Michael was not happy with either of the 2 proposals and decided to set stricter time constraints and asked the agent to try again. – One therapist had offered appointments in two weeks’ time – For the other one Michael would have to drive during rush hour.

Chapter 1A Semantic Web Primer, 2nd Edition 1-25 Personal Agents in the Semantic Web The agent came back with an alternative solution: – A therapist with an excellent reputation who had available appointments starting in 2 days

Chapter 1A Semantic Web Primer, 2nd Edition 1-26 Personal Agents in the Semantic Web However, there were still a few minor problems with the alternative solution – Some of Michael’s less important work appointments would have to be rescheduled. – The agent offered to make arrangements if this solution were adopted. – The therapist was not listed on the insurer’s site because he charged more than the insurer’s maximum coverage.

Chapter 1A Semantic Web Primer, 2nd Edition 1-27 Personal Agents in the Semantic Web The agent had: – found his name from an independent list of therapists – checked that Michael was entitled to the insurer’s maximum coverage, according to the insurer’s policy – negotiated with the therapist’s agent a special discount The therapist had only recently decided to charge more than average and was keen to find new patients.

Chapter 1A Semantic Web Primer, 2nd Edition 1-28 Personal Agents in the Semantic Web Michael was happy with the recommendation because he would have to pay only a few dollars extra. However, because he had installed the Semantic Web agent a few days ago, he asked it for explanations of some of its assertions: – how was the therapist’s reputation established – why was it necessary for Michael to reschedule some of his work appointments – how was the price negotiation conducted

Chapter 1A Semantic Web Primer, 2nd Edition 1-29 Personal Agents in the Semantic Web The agent provided appropriate information. Michael was satisfied. – His new Semantic Web agent was going to make his busy life easier. – He asked the agent to take all necessary steps to finalize the task.

Chapter 1A Semantic Web Primer, 2nd Edition 1-30 Lecture Outline 1. Today’s Web 2. The Semantic Web Impact 3. Semantic Web Technologies 4. A Layered Approach 5. The Semantic Web Today

Chapter 1A Semantic Web Primer, 2nd Edition 1-31 Semantic Web Technologies Explicit Metadata Ontologies Logic and Inference Agents

Chapter 1A Semantic Web Primer, 2nd Edition 1-32 On HTML Web content is currently formatted for human readers rather than programs HTML is the predominant language in which Web pages are written (directly or using tools) Vocabulary of HTML describes presentation

Chapter 1A Semantic Web Primer, 2nd Edition 1-33 An HTML Example Agilitas Physiotherapy Centre Welcome to the home page of the Agilitas Physiotherapy Centre. Do you feel pain? Have you had an injury? Let our staff Lisa Davenport, Kelly Townsend (our lovely secretary) and Steve Matthews take care of your body and soul. Consultation hours Mon 11am - 7pm Tue 11am - 7pm Wed 3pm - 7pm Thu 11am - 7pm Fri 11am - 3pm But note that we do not offer consultation during the weeks of the State Of Origin games.

Chapter 1A Semantic Web Primer, 2nd Edition 1-34 Problems with HTML Humans have no problem with this Machines (software agents) do: – How distinguish therapists from the secretary – How determine exact consultation hours – They would have to follow the link to the State Of Origin games to find when they take place.

Chapter 1A Semantic Web Primer, 2nd Edition 1-35 A Better Representation Physiotherapy Agilitas Physiotherapy Centre Lisa Davenport Steve Matthews Kelly Townsend

Chapter 1A Semantic Web Primer, 2nd Edition 1-36 Explicit Metadata This representation is far more easily processable by machines Metadata: data about data – Metadata capture part of the meaning of data Semantic Web does not rely on text-based manipulation, but rather on machine- processable metadata

Chapter 1A Semantic Web Primer, 2nd Edition 1-37 User Adoption Users will not have to be computer science experts to develop Web pages with metadata – They will be able to use tools for this purpose. Why users should abandon HTML for Semantic Web languages?

Chapter 1A Semantic Web Primer, 2nd Edition 1-38 User Adoption Compare situation today to the beginnings of the Web. – The first users decided to adopt HTML because it had been adopted as a standard and they were expecting benefits from being early adopters. – Others followed when more and better Web tools became available. – Soon HTML was a universally accepted standard.

Chapter 1A Semantic Web Primer, 2nd Edition 1-39 User Adoption Similarly, we are currently observing the early adoption of XML. – Provides a surface syntax for structured documents – Imposes no semantic constraints on the meaning of these documents. – XML Schema is a language for restricting the structure of XML documents. While not sufficient in itself for the realization of the Semantic Web vision, XML is an important first step.

Chapter 1A Semantic Web Primer, 2nd Edition 1-40 User Adoption Early users (e.g. large organizations interested in knowledge management and B2B e-commerce) will adopt XML and RDF, the current SW standards. The momentum will lead to more tool vendors’ and end users’ adopting the technology. – This will be a decisive step in the Semantic Web venture, but it is also a challenge. – The greatest current challenge is not scientific but rather one of technology adoption.

Chapter 1A Semantic Web Primer, 2nd Edition 1-41 Ontologies The term ontology originates from philosophy The study of the nature of existence Different meaning from computer science An ontology is an explicit and formal specification of a conceptualization

Chapter 1A Semantic Web Primer, 2nd Edition 1-42 Typical Components of Ontologies Terms denote important concepts (classes of objects) of the domain – e.g. professors, staff, students, courses, departments Relationships between these terms: typically class hierarchies – a class C to be a subclass of another class C' if every object in C is also included in C' – e.g. all professors are staff members

Further Components of Ontologies Properties: – X’s phone number is Relationships – X teaches Y Value restrictions – only faculty members can teach courses Disjointness statements – faculty and general staff are disjoint Logical relationships between objects – every department must include at least 10 faculty 1-43 A Semantic Web Primer, 2nd EditionChapter 1

A Semantic Web Primer, 2nd Edition 1-44 Example of a Class Hierarchy

Chapter 1A Semantic Web Primer, 2nd Edition 1-45 The Role of Ontologies on the Web Ontologies provide a shared understanding of a domain: – semantic interoperability – overcome differences in terminology – mappings between ontologies Ontologies are useful for the organization and navigation of Web sites

Chapter 1A Semantic Web Primer, 2nd Edition 1-46 The Role of Ontologies in Web Search Ontologies are useful for improving the accuracy of Web searches – search engines can look for pages that refer to a precise concept in an ontology Web searches can exploit generalization/ specialization information – If a query fails to find any relevant documents, the search engine may suggest to the user a more general query. – If too many answers are retrieved, the search engine may suggest to the user some specializations.

Chapter 1A Semantic Web Primer, 2nd Edition 1-47 Web Ontology Languages RDF Schema RDF is a data model for objects and relations between them RDF Schema is a vocabulary description language Describes properties and classes of RDF resources Provides semantics for generalization hierarchies of properties and classes

Chapter 1A Semantic Web Primer, 2nd Edition 1-48 Web Ontology Languages (2) OWL A richer ontology language relations between classes – e.g., disjointness cardinality – e.g. “exactly one” richer typing of properties characteristics of properties (e.g., symmetry)

Chapter 1A Semantic Web Primer, 2nd Edition 1-49 Logic and Inference Logic is the discipline that studies the principles of reasoning Formal languages for expressing knowledge Well-understood formal semantics – Declarative knowledge: we describe what holds without caring about how it can be deduced Automated reasoners can deduce (infer) conclusions from the given knowledge

Chapter 1A Semantic Web Primer, 2nd Edition 1-50 An Inference Example prof(X)  faculty(X) faculty(X)  staff(X) prof(michael) We can deduce the following conclusions: faculty(michael) staff(michael) prof(X)  staff(X)

Chapter 1A Semantic Web Primer, 2nd Edition 1-51 Logic versus Ontologies The previous example involves knowledge typically found in ontologies – Logic can be used to uncover ontological knowledge that is implicitly given – It can also help uncover unexpected relationships and inconsistencies Logic is more general than ontologies – It can also be used by intelligent agents for making decisions and selecting courses of action

Chapter 1A Semantic Web Primer, 2nd Edition 1-52 Tradeoff between Expressive Power and Computational Complexity The more expressive a logic is, the more com- putationally expensive it becomes to draw conclusions – Drawing certain conclusions may become impos- sible if non-computability barriers are encountered. Previous examples involved rules “If conditions, then conclusion,” and only finitely many objects – This subset of logic is tractable and is supported by efficient reasoning tools

Chapter 1A Semantic Web Primer, 2nd Edition 1-53 Inference and Explanations Explanations: the series of inference steps can be retraced They increase users’ confidence in Semantic Web agents: – “Oh yeah?” button Activities between agents: create or validate proofs

Chapter 1A Semantic Web Primer, 2nd Edition 1-54 Typical Explanation Procedure Facts will typically be traced to some Web addresses – The trust of the Web address will be verifiable by agents Rules may be a part of a shared commerce ontology or the policy of the online shop

Chapter 1A Semantic Web Primer, 2nd Edition 1-55 Example of Explanation between Agents Agent 1 (online shop) sends a message “You owe me $80” to agent 2 (person). – Not in natural language, but in a formal, machine-processable language

Chapter 1A Semantic Web Primer, 2nd Edition 1-56 Example of Explanation between Agents Then agent 2 asks for an explanation, and agent 1 responds with a sequence: – Web log of a purchase over $80 – Proof of delivery (e.g., tracking number of UPS) – Rule from the shop’s terms and conditions: purchase(X,Item)  price(Item, Price)  delivered(Item,X)  owes(X, Price)

Chapter 1A Semantic Web Primer, 2nd Edition 1-57 Software Agents Software agents work autonomously and proactively – They evolved out of object oriented and component-based programming A personal agent on the Semantic Web will: – receive some tasks and preferences from the person – seek information from Web sources, communicate with other agents – compare information about user requirements and preferences, make certain choices – give answers to the user

Chapter 1A Semantic Web Primer, 2nd Edition 1-58 Intelligent Personal Agents

Chapter 1A Semantic Web Primer, 2nd Edition 1-59 Semantic Web Agent Technologies Metadata – Identify and extract information from Web sources Ontologies – Web searches, interpret retrieved information – Communicate with other agents Logic – Process retrieved information, draw conclusions

Chapter 1A Semantic Web Primer, 2nd Edition 1-60 Semantic Web Agent Technologies (2) Further technologies (orthogonal to the Semantic Web technologies) – Agent communication languages – Formal representation of beliefs, desires, and intentions of agents – Creation and maintenance of user models.

Chapter 1A Semantic Web Primer, 2nd Edition 1-61 Lecture Outline 1. Today’s Web 2. The Semantic Web Impact 3. Semantic Web Technologies 4. A Layered Approach 5. The Semantic Web Today

Chapter 1A Semantic Web Primer, 2nd Edition 1-62 A Layered Approach The development of the Semantic Web proceeds in steps – Each step building a layer on top of another Principles: Downward compatibility Upward partial understanding

Chapter 1A Semantic Web Primer, 2nd Edition 1-63 The Semantic Web Layer Tower

Chapter 1A Semantic Web Primer, 2nd Edition 1-64 Semantic Web Layers XML layer – Syntactic basis (send docs across the Web) RDF layer – RDF basic data model for facts – Does not rely on XML, but has XML-based syntax – RDF Schema simple ontology language Ontology layer – More expressive languages than RDF Schema – Current Web standard: OWL

Chapter 1A Semantic Web Primer, 2nd Edition 1-65 Semantic Web Layers (2) Logic layer – enhance ontology languages further – application-specific declarative knowledge Proof layer – Proof generation, exchange, validation Trust layer – Digital signatures – recommendations, rating agencies ….

Chapter 1A Semantic Web Primer, 2nd Edition 1-66 Web of Trust Trust will be organized in the same distributed and chaotic way as the WWW Trust is a high-level and crucial concept (top of the pyramid) The Web will only achieve its full potential when users have trust in its operations (security) and in the quality of information provided.

Newer SW Architectures – v2 Chapter 1A Semantic Web Primer, 2nd Edition 1-67

Newer SW Architectures – v3 Chapter 1A Semantic Web Primer, 2nd Edition 1-68

Newer SW Architectures – v4 Chapter 1A Semantic Web Primer, 2nd Edition 1-69

Alternative SW architectures – non TBL [Horrocks et al., 2005]/v1 Chapter 1A Semantic Web Primer, 2nd Edition 1-70

Alternative SW architectures – non TBL [Horrocks et al., 2005]/v2 Chapter 1A Semantic Web Primer, 2nd Edition 1-71

Alternative SW architectures – non TBL [Gerber et al., 2008] Chapter 1A Semantic Web Primer, 2nd Edition 1-72

Lecture Outline 1. Today’s Web 2. The Semantic Web Impact 3. Semantic Web Technologies 4. A Layered Approach 5. The Semantic Web Today 1-73 Chapter 1A Semantic Web Primer, 2nd Edition

Could Semantic Web become a reality? Almost every major Web company has now announced their work on a knowledge graph – Google Knowledge Graph – Yahoo! Web of Objects – Walmart Lab Social Genome – Microsoft Satori Graph / Bing Snapshots – Facebook Entity Graph 1-74 Chapter 1A Semantic Web Primer, 2nd Edition

DBPedia DBpedia is a community-run project to build a free, open-source knowledge graph since – Effort to extract structured information from Wikipedia and make this information available on the Web. DBpedia allows you to ask sophisticated queries against Wikipedia, and to link the different data sets on the Web to Wikipedia data. – It will be easier for the huge amount of information in Wikipedia to be used in some interesting new ways. DBpedia currently exists in 125 different languages, and is interlinked with many other databases – e.g. Freebase, GeoNames, New York Times, Wikidata 1-75 Chapter 1A Semantic Web Primer, 2nd Edition

Linked Data The knowledge in DBpedia is exposed through a set of technologies called Linked Data. Linked Data has been revolutionizing the way applications interact with the Web. Web 2.0 technologies allowed websites to be re-used from third-parties and to repurpose data on the Web, – Still require that developers create one client per target API With Linked Data, all APIs are interconnected via standard Web protocols and languages Chapter 1A Semantic Web Primer, 2nd Edition

Linked Data benefits One can navigate this Web of facts (or Web of Data) with standard Web browsers, automated crawlers or pose complex queries with SQL-like query languages (e.g. SPARQL). – Have you thought of asking the Web about all cities with low criminality, warm weather and open jobs? 1-77 Chapter 1A Semantic Web Primer, 2nd Edition

Linked Data benefits New Web of interlinked databases provides useful knowledge that can complement textual Web E.g. bloggers tag their posts or assign them to categories in order to organize and interconnect their blog posts. – This is a very simple way to connect “unstructured” text to a structure (hierarchy of tags). – Identifiers and data provided by DBpedia were greatly involved in creating this knowledge graph. IBM's Watson used DBpedia data to win the Jeopardy challenge 1-78 Chapter 1A Semantic Web Primer, 2nd Edition

Schema.org Using Ontologies in practice Schema.org provides a collection of schemas, i.e., html tags, that webmasters can use to markup their pages in ways recognized by major search providers. – Search engines including Bing, Google, Yahoo! and Yandex rely on this markup to improve the display of search results, making it easier for people to find the right web pages. Many sites are generated from structured data, which is often stored in databases. – When this data is formatted into HTML, it becomes very difficult to recover the original structured data. – Many applications, especially search engines, can benefit greatly from direct access to this structured data Chapter 1A Semantic Web Primer, 2nd Edition

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Schema.org Using Ontologies in practice On-page markup enables search engines to understand the information on web pages and provide richer search results to make it easier for users to find relevant information on the web. – Markup can also enable new tools and applications that make use of the structure. A shared markup vocabulary makes it easier for webmasters to decide on a markup schema and get the maximum benefit for their efforts. – Search engines have come together to provide a shared collection of schemas that webmasters can use Chapter 1A Semantic Web Primer, 2nd Edition

Schema.org and Linked Data Actually, information in tagged HTML pages can become linked data (RDF) – Using extraction tools Schema.RDFS.org provides a common ontology that these linked data conform to There exist mappings from schema.org terms to the DBPedia ontology 1-82 Chapter 1A Semantic Web Primer, 2nd Edition

Example of incorporating metadata in a web page Chapter 1A Semantic Web Primer, 2nd Edition 1-83

Example of metadata in a web page: XHTML+RDFa code for content & metadata Chapter 1A Semantic Web Primer, 2nd Edition 1-84

Example of metadata in a web page: RDF/XML code for metadata Chapter 1A Semantic Web Primer, 2nd Edition 1-85

Example of metadata in a web page: Metadata in RDF N-triples format Chapter 1A Semantic Web Primer, 2nd Edition 1-86

Example of metadata in a web page: RDF metadata in a graph (semantic net) Chapter 1A Semantic Web Primer, 2nd Edition 1-87

Some Semantic Web Applications Chapter 1A Semantic Web Primer, 2nd Edition 1-88

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SPLIS A Rule-Based Semantic Personalized Location Information System Chapter 1A Semantic Web Primer, 2nd Edition 1-93

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University Rankings 1-95 Chapter 1A Semantic Web Primer, 2nd Edition

Find unique (?) DBPedia URL 1-96 Chapter 1A Semantic Web Primer, 2nd Edition

Using the DBPedia lookup service 1-97 Chapter 1A Semantic Web Primer, 2nd Edition

Using a SPARQL endpoint 1-98 Chapter 1A Semantic Web Primer, 2nd Edition

Chapter 1A Semantic Web Primer, 2nd Edition 1-99 Book Outline 2. Structured Web Documents in XML 3. Describing Web Resources in RDF 4. Web Ontology Language: OWL 5. Logic and Inference: Rules 6. Applications 7. Ontology Engineering 8. Conclusion and Outlook

Chapter 1A Semantic Web Primer, 2nd Edition SW vs. AI Most SW technologies build upon work in the area of AI – AI has a long history, not always commercially successful. – People worry that the SW will repeat AI’s errors: Big promises that raise too high expectations, which turn out not to be fulfilled. The realization of the SW vision does not rely on human-level intelligence – The challenges are approached in a different way.

Chapter 1A Semantic Web Primer, 2nd Edition SW vs. AI Τhe ultimate goal of AI is to build an intelligent agent exhibiting human-level intelligence (and higher) – Τhe goal of SW is to assist human users in their day-to-day online activities – Even if an intelligent agent is not able to come to all conclusions that a human user might draw, the agent will still contribute to a Web much superior to the current Web.

Chapter 1A Semantic Web Primer, 2nd Edition SW vs. AI Semantic Web will make extensive use of current AI technology – Advances in AI technology will lead to a better Semantic Web. – There is no need to wait until AI reaches a higher level of achievement – Current AI technology is already sufficient to go a long way toward realizing the Semantic Web vision.