Semantic Web Technologies

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

http://www.ischool.utexas.edu/~i385t-sw

Semantic Technologies StackSemantic Technologies Stack

Semantic Web elementsSemantic 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

http://www.w3.org/RDF/

http://www.daml.org/



http://www.w3.org/TR/xhtml1/

http://www.gbiv.com/protocols/uri/rfc/rfc3986.html



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








Structure is (still) the gatewayStructure 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)

Documents are the StructureDocuments are the Structure• XML: markup

language for encoding semantics

• Everyone understands XML- Especially browsers &

Web crawlers- Or thinks they do,

which still expands adoption

<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: Lingua Franca for SWTXML: 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, …

The XML PhilosophyThe 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

XML SchemasXML 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)

XML Schema SpecificsXML 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

XML NamespacesXML 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">

Schemas & InstancesSchemas & Instances

Document Object ModelDocument 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

Resource Description FrameworkResource 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

RDF GrammarRDF 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.

RDF BarriersRDF 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

XpathXpath• 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

Xquery & XformsXquery & 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

More Semantic StandardsMore 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

Feed Readers & blog postingFeed Readers & blog posting• How do you use Semantic Web technologies?- Browsing- Retrieval- Sharing

• Readers• Blogging is easy

What isn’t the Semantic Web?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?

Topic SelectionTopic 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

Current list of TopicsCurrent 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

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