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Semantic Web Technologies

Semantic Web Technologies . Web Site syllabus still developing http://www.ischool.utexas.edu/~i385t-sw Readings Discussion Discussion: What isn't the Semantic Web? Class work: Using feed reader applications and blog posting demonstrations Research Presentation Topics.

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Semantic Web Technologies

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  1. Semantic Web Technologies • Web Site syllabus still developing • http://www.ischool.utexas.edu/~i385t-sw • Readings Discussion • Discussion: What isn't the Semantic Web? • Class work: Using feed reader applications and blog posting demonstrations • Research Presentation Topics

  2. Semantic Technologies Stack

  3. Semantic Web elements • XML • Structured markup languages • RDF • DAML + OIL • XHTML • Universal Resource Identifiers • URLs of course • Structured, parsable addressing • http://www.shadows.com/tags/semantic_web • http://www.flickr.com/photos/tags/austin • http://www.amazon.com/exec/obidos/external-search/103-3992378-7183068?keyword=ajax&tag=donturnbullweb&mode=books

  4. Structure is (still) the gateway • Web Services • The URI describes the functional parameters • The system does the REST • The client is a smart interpreter of the results • Web services have a grammar • Defined by standards • Initiated by the URI • The request • Implemented by the system • The supplied • Logic, Classification & Ontologies all provide additional functionality & structure • Never underestimate the power of plain text • Machine readable w/o extra work • Human understandable (for lightweight semantics)

  5. Documents are the Structure <CATALOG> <CD> <TITLE>Empire Burlesque</TITLE> <ARTIST>Bob Dylan</ARTIST> <COUNTRY>USA</COUNTRY> <COMPANY>Columbia</COMPANY> <PRICE>10.90</PRICE> <YEAR>1985</YEAR> </CD> <CD> <TITLE>Hide your heart</TITLE> <ARTIST>Bonnie Tyler</ARTIST> <COUNTRY>UK</COUNTRY> <COMPANY>CBS Records</COMPANY> <PRICE>9.90</PRICE> <YEAR>1988</YEAR> </CD> … • XML: markup language for encoding semantics • Everyone understands XML • Especially browsers & Web crawlers • Or thinks they do, which still expands adoption

  6. XML: Lingua Franca for SWT • “XML may become the primary syntax for all enterprise data” p 27-28 • Application independent • Standard syntax for metadata • Standard structure for documents & data • It’s already in use • It isn’t about the CPU, it’s about being open • Structured documents use logic for semantic descriptions • And it’s not all about metadata • If it’s not easily readable, you get a legend • Schemas, DTDs, …

  7. The XML Philosophy • XML is the syntax guidelines for markup • Common structural elements are specific to each genre of use • Markup is based on elements • A container with start and end tags • Elements can have sub elements • Roots & trees • Roots define the structure • Trees are the hierarchy within • Inheritance defines the relationships • Like HTML, but stricter with the structure (XHTML) • Validated XML (or XHTML) means it is usable, not correct • XML Schemas are the specific rules for validation

  8. XML Schemas • A “definition language” to constrain semantic vocabulary & hierarchical structure • Taken from database schemas, that defines the data types, fields & tables in a DBMS • Most are not complex • But validation is key to making Semantics useful • Schemas by another name: • Document Type Definition (DTD) • RELAX NG • Schematron (XPath)

  9. XML Schema Specifics • An XML Schema defines: • elements that can appear in a document • attributes that can appear in a document • which elements are child elements • the order of child elements • the number of child elements • whether an element is empty or can include text • data types for elements & attributes • default and fixed values for elements & attributes

  10. XML Namespaces • Namespaces define the markup globals • Building blocks: metadata & local <xsd: integer> • Calls from others • <xsd: schema xmlns:xsd:http://www.w3.org/2001/XMLSchema targetNamespace=http://www.utexas.edu/markup> • What you commonly see: • <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en-US" lang="en-US">

  11. Schemas & Instances

  12. Document Object Model • Part of the machine executable rules of the markup language & schema • Controls behavior in Web browsers too • DOM Level 3 supports Semantics • We’ll see more about the DOM in later weeks • Web 2.0, AJAX & REST rely on it heavily

  13. Resource Description Framework • What’s not a Resource? • That’s good & bad • “RDF captures meta data about the ‘externals’ of a document, like the author, the creation date, and type” p 85 • Non-text & discrete objects (images, music, bookmarks) • A triplet defining anything • Subject • Predicate • Object

  14. RDF Grammar • Describing the author of a document • http://www.utexas.edu/index.html has a author whose value is Don Turnbull • the RDF terms for the various parts of the statement are: • the subject is the URL http://www.utexas.edu/index.html • the predicate is the word author • the object is the phrase “Don Turnbull” • Describing knowledge is subtle, metadata definition is not always easy.

  15. RDF Barriers • People don’t use reification well or at all (provenance metadata) • Inheritance is tricky & the logic must be parsed • Containers are very flexible • Bags allow any order • Sequences can be more complex than alphabetical • Alternates depend on the instance • Syntax is varied • Examples are “simple”, but still not completely utilized • Dublin Core • RSS • Tools will help as will industry use • Podcasts (Media RSS) • More on this and RDF Schemas themselves later

  16. Xpath • Control syntax for all manner of XML interaction & addressing • Allows for finding, parsing & manipulating data in a document • See XSLT • Examples: • selects the document root (which is always the parent of the document element) • child::para selects the para element children of the context node

  17. Xquery & Xforms • A structured query language for XML • Allows for building virtual documents from parts of other documents • Understands the rules of schemas, markup & metadata to perform application-level functions on data • Tool support is growing including DBMS vendors • Works with Xforms to provide RDBMS access to URI addressable data

  18. More Semantic Standards • Xlink • Conditional link syntax far beyond anchors & addressing • Xpointer • Allows for building (& including) aggregated, distributed applications & interfaces • Xinclude • Provides “make file” syntax for building master documents or constructing complex Semantic inheritance & interaction • XMLBase • Syntax for resolving & recommending relevant URIs • Style Sheets • XSL • XSLT • XSLFO

  19. Feed Readers & blog posting • How do you use Semantic Web technologies? • Browsing • Retrieval • Sharing • Readers • Blogging is easy

  20. What isn’t the Semantic Web? • “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” (Berners-Lee, 2001) • What do you think now? • How promising can SWT be? • As everyday systems • Is it a new way to solve problems? • Or • A new set of capabilities & solutions?

  21. Topic Selection • Choose a topic (and corresponding week) to overview • Topic Presentations should include: • Overview of the technology • Provide examples of the technology in use • Show how to build using the technology (examples) • A list of citations and readings that you drew from and for extended reference • Do not rely on wikipedia & blogs as your only sources • Academic journal & conference papers • Books (development or conceptual design) • How can these Semantic Web technologies help coordinate, discover, organize information and knowledge? • Your own point of view about the practicality & promise of these tools & procedures

  22. Current list of Topics • RDF • Metadata (e.g. Dublin Core, MediaRSS) • Ontology building (applications) • REST, XMLHttpRequest & AJAX • Greasemonkey • Javascript: Introduction • Javascript: Advanced • TagClouds • GIS, Maps & Mapping Mashups • XSLT • WordNet • Semantic Commerce • Trust

  23. Next Week • Readings & Discussion • Blogging & Tagging (ongoing) • Finalize topics & presentation dates • Suggestions for speakers

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