Introduction to Web Science

1. Introduction to Web Science Maintaining Information on the Web

2. Six challenges of the Knowledge Life Cycle • Acquire • Model • Reuse • Retrieve • Publish • Maintain

3. Prediction • Ontology maintenance will become the significant problem as ontologies become more mainstream • High quality ontologies are easier to maintain

4. What makes a good quality ontology? • Coverage • Correctness • Consistency • Richness • Organisation • Relation to reality • Making meaning clear

5. Common modelling pitfalls • Instantiation • Constitution • Composition • Disjunction • Polysemy

6. Instantiation (1) • Which one is correct?

7. Instantiation (2) • Question • What PDA model do you sell? • Answer • My PDA is not a PDA model! • So you wouldn’t sell your PDA!

8. Composition (1) • What’s incorrect with this?

9. Composition (2) • Question • What computers do you sell? • Answer • Definitely not disk drives and memory is the answer!

10. Disjunction (1)

11. Disjunction (2)

12. Disjunction (2)

13. Disjunction (3)

14. Polysemy (1) • Words with more than one meaning … • What is a book? • A physical object • “The DaVinci Code” • An abstract entity • A Book by Dan Brown

15. Polysemy (2) • We must be consistent with what is a book!

16. Constitution (1) • Computer should not form part of the hierarchy, different level of constitution

17. Constitution (2) • What kind of matter conducts electricity? • Answer should not be computer

18. Making Meaning Clear • Part-of relates parts to their wholes • E.g. part-of(engine,car) • Part-of is irreflexive • Part-of is anti-symmetric • Nothing can have only one part

19. Requirement for Ontology Management(1/2) • Ontology management • Stored, aligned, evolution need to be managed • Alignment • the ontologies either need to be integrated • Because, re-used • Ontology alignment is very relevant in a Semantic Web context • separate ontologies should be aligned and linked

20. Requirement for Ontology Management(2/2) • Support for evolving ontologies • change in the real world (E.g. Car engines) • adaptations to different tasks (E.g. Wine and food) • alignments to other ontologies (E.g. Travel and food) • Ontology library systems • grouping, reorganizing ontologies for further re-use • integration, maintenance, mapping, versioning

21. Aligning Ontologies (1) • Why is Aligning Needed • created to link different terminologies (E.g. books) • modeling styles used in these domain specific ontologies • creating bridges between separated pieces of knowledge

22. (The alignments) Aligning Ontologies (2) • Aligning Annotated XML Documents

23. Supporting Ontology Change (1) • Ontologies specific • Not static, evolution is need • Reasons of changes in ontologies • Changes in the domain • Change in the real world • Domain to be modified • Changes in the conceptualization • Different perspective • E.g. Pet shop vrs Reptile Ontology • Changes in the specification • Translation – retain the semantics

24. Supporting Ontology Change (2) • Changes in ontologies involve Several Problems • Effects of Ontology Change • Different interpretation or may use unknown terms • Changes to the source ontology • Applications that use the ontology may also be hampered

25. Supporting Ontology Change (3) • Change Management • Comparing Ontologies • Logical definition change • Non-logical change • Identifier change • Addition of definitions • Deletion of definitions • Specification of Change • Transformation or actual change • Conceptual relation • Descriptive meta-data like date, author, and reason of the update • Valid context

26. Organising Ontologies (1) • Different ontologies increasing • Task of storing • Maintaining and re-organizing • Ontology library system • Tool in grouping and re-organizing ontologies • Re-use, integration, maintenance and versioning

27. Organising Ontologies (2) • Sesame • Open storage, identification and versioning of ontologies • Smooth access to existing ontologies and advanced support in adapting ontologies to certain domain and task-specific circumstances • Fully employing the power of standardization and providing access to upper-layer ontologies and standard representation languages

28. Organising Ontologies (3) • Sesame Requirements (Aspects of an ontology library system)

29. Organising Ontologies (4) • Functionality of an Ontology Storage System • Management • Storage • easily accessible • Ontologies classified • Stored in modules (because ontology re-use) • Identification • Unique identifier • Versioning • Ensuring consistency

30. Organising Ontologies (5) • Functionality of an Ontology Storage System • Adaptation • Searching • how to search ontology • Editing • how to add, delete and edit specific ontologies • Reasoning • How to derive consequences from an ontology

31. Organising Ontologies (6) • Functionality of an Ontology Storage System • Standardization • Language • Kind of standard ontology language used in the ontology library system • E.g. RDFS, XMLS, DAML+OIL • Upper-level Ontologies

32. Organising Ontologies (7) • Current storage systems • Adaptation • Searching • Access through the Internet or World Wide Web • Offer Simple browsing only • SQL-based searching • Editing • Simple editing function • Reasoning • Very simple reasoning function • E.g. WebOnto(rule-based reasoning), Ontolingua (ontology testing), SHOE(ontology revision)

33. Organising Ontologies (8) • Requirement for a Storage System • Other requirements • Ontology scalability • Maintenance facility • Explicit documentation

34. Translating between Ontologies • XSLT stands for Extensible Stylesheet Language Transformations • XSLT is used to transform XML documents into other kinds of documents--usually, but not necessarily, XHTML • XSLT uses two input files: • The XML document containing the actual data • The XSL document containing both the “framework” in which to insert the data, and XSLT commands to do so

35. Very simple example • File data.xml: • <?xml version="1.0"?><?xml-stylesheet type="text/xsl" href="render.xsl"?><message>Howdy!</message> • File render.xsl: • <?xml version="1.0"?><xsl:stylesheet version="1.0” xmlns:xsl="http://www.w3.org/1999/XSL/Transform"><!-- one rule, to transform the input root (/) --> <xsl:template match="/"><html><body><h1><xsl:value-of select="message"/></h1> </body></html> </xsl:template></xsl:stylesheet>

36. The .xsl file • An XSLT document has the .xsl extension • The XSLT document begins with: • <?xml version="1.0"?> • <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/ XSL/Transform"> • Contains one or more templates, such as: • <xsl:template match="/"> ... </xsl:template> • And ends with: • </xsl:stylesheet>

37. Finding the message text • The template <xsl:template match="/"> says to select the entire file • You can think of this as selecting the root node of the XML tree • Inside this template, • <xsl:value-of select="message"/> selects the message child • Alternative Xpath expressions that would also work: • ./message • /message/text() (text() is an XPath function) • ./message/text()

38. Putting it together • The XSL was: <xsl:template match="/"> <html><body> <h1><xsl:value-of select="message"/></h1> </body></html> </xsl:template> • The <xsl:template match="/"> chooses the root • The <html><body> <h1> is written to the output file • The contents of message is written to the output file • The </h1> </body></html> is written to the output file • The resultant file looks like:<html><body> <h1>Howdy!</h1> </body></html>

39. How XSLT works • The XML text document is read in and stored as a tree of nodes • The <xsl:template match="/"> template is used to select the entire tree • The rules within the template are applied to the matching nodes, thus changing the structure of the XML tree • Unmatched parts of the XML tree are not changed • After the template is applied, the tree is written out again as a text document

40. Where XSLT can be used • With an appropriate program, such as Xerces, XSLT can be used to read and write files • A server can use XSLT to change XML files into HTML files before sending them to the client • A modern browser can use XSLT to change XML into HTML on the client side • Most users seldom update their browsers • If you want “everyone” to see your pages, do any XSL processing on the server side • Otherwise, think about what best fits your situation

41. xsl:value-of • <xsl:value-of select="XPath expression"/> selects the contents of an element and adds it to the output stream • The select attribute is required • Example (from an earlier slide): • <h1> <xsl:value-of select="message"/> </h1>

42. xsl:for-each • xsl:for-each is a kind of loop statement • The syntax is <xsl:for-each select="XPath expression">Text to insert and rules to apply </xsl:for-each> • Example: to select every book element irrespective of where it is (//book) and make an unordered list (<ul>) of their titles (title), use: <ul> <xsl:for-each select="//book"> <li> <xsl:value-of select="title"/> </li> </xsl:for-each> </ul>

43. Filtering output • You can filter (restrict) output by adding a criterion to the select attribute’s value: <ul> <xsl:for-each select="//book"> <li> <xsl:value-of select="title[../author=‘Dan Brown']"/> </li> </xsl:for-each> </ul>

44. Filter details • Here is the filter we just used:<xsl:value-of select="title[../author=‘Dan Brown'"]/> • author is a sibling of title, so from title we have to go up to its parent, book, then back down to author • This filter requires a quote within a quote, so we need both single quotes and double quotes • Legal filter operators are:= != &lt; &gt;

45. But it doesn’t work right! • Here’s what we did: <xsl:for-each select="//book"> <li> <xsl:value-of select="title[../author=‘Dan Brown']"/> </li> </xsl:for-each> • This will output <li> and </li> for every book, so we will get empty bullets for authors other than Dan Brown • There is no obvious way to solve this with just xsl:value-of

46. xsl:if • xsl:if allows us to include content if a given condition (in the test attribute) is true • Example: <xsl:for-each select="//book"> <xsl:if test="author=‘Dan Brown'"> <li> <xsl:value-of select="title"/> </li> </xsl:if> </xsl:for-each> • This does work correctly!

47. xsl:choose • The xsl:choose ... xsl:when ... xsl:otherwise construct is XML’s equivalent of Java’s switch ... case ... default statement • The syntax is:<xsl:choose> <xsl:when test="some condition">... some code ... </xsl:when> <xsl:otherwise>... some code ... </xsl:otherwise></xsl:choose>

48. xsl:sort • You can place an xsl:sort inside an xsl:for-each • The attribute of the sort tells what field to sort on • Example: <ul> <xsl:for-each select="//book"> <xsl:sort select="author"/> <li> <xsl:value-of select="title"/> by <xsl:value-of select="author"> </li> </xsl:for-each> </ul> • This example creates a list of titles and authors, sorted by author

49. xsl:text • <xsl:text>...</xsl:text> helps deal space related problems: • XSL isn’t very careful with whitespace in the document • This doesn’t matter much for HTML, which collapses all whitespace anyway (though the HTML source may look ugly) • <xsl:text> gives you much better control over whitespace; it acts like the <pre> element in HTML

50. Creating tags from XML data • Suppose the XML contains <name>Dr. Dave's Home Page</name><url>http://www.cis.upenn.edu/~matuszek</url> • And you want to turn this into<a href="http://www.cis.upenn.edu/~matuszek">Dr. Dave's Home Page</a> • We need additional tools to do this