Semantic Web Technologies Web Site syllabus still developing Readings Discussion Discussion: What isn't the Semantic Web? Class work: Using feed reader applications and blog posting demonstrations Research Presentation Topics

Semantic Technologies Stack

Semantic Web elements XML - Structured markup languages RDF DAML + OIL XHTML - Universal Resource Identifiers Universal Resource Identifiers URLs of course Structured, parsable addressing search/ ?keyword=ajax&tag=donturnbullweb&mode=b ookshttp:// search/ ?keyword=ajax&tag=donturnbullweb&mode=b ooks

Structure is (still) the gateway Web Services - The URI describes the functional parameters - The system does the RESTREST - 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 Structure XML: markup language for encoding semantics Everyone understands XML - Especially browsers & Web crawlers - Or thinks they do, which still expands adoption Empire Burlesque Bob Dylan USA Columbia Hide your heart Bonnie Tyler UK CBS Records …

XML: Lingua Franca for SWT “XML may become the primary syntax for all enterprise data” p 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 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 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 RELAX NG - Schematron (XPath) Schematron

XML Schema Specifics An XML Schema defines: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 Namespaces Namespaces define the markup globals - Building blocks: metadata & local - Calls from others - What you commonly see: -

Schemas & Instances

Document Object Model Part of the machine executable rules of the markup language & schema Controls behavior in Web browsers toobehavior in Web browsers 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 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 Grammar Describing the author of a document has a author whose value is Don Turnbull the RDF terms for the various parts of the statement are: - the subject is the URL - the predicate is the word author - the object is the phrase “Don Turnbull” Describing knowledge is subtle, metadata definition is not always easy.

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

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

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

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

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

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