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

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

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