Semantic Web TechnologiesSemantic Technologies StackSemantic Web elementsStructure is (still) the gatewayDocuments are the StructureXML: Lingua Franca for SWTThe XML PhilosophyXML SchemasXML Schema SpecificsXML NamespacesSchemas & InstancesDocument Object ModelResource Description FrameworkRDF GrammarRDF BarriersXpathXquery & XformsMore Semantic StandardsFeed Readers & blog postingWhat isn’t the Semantic Web?Topic SelectionCurrent list of TopicsNext WeekSemantic 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 TopicsSemantic Technologies StackSemantic Technologies StackSemantic 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=booksStructure 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 validationXML 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 & attributesXML 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 & InstancesDocument 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 heavilyResource 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•ObjectRDF 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 laterXpathXpath•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 nodeXquery & 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 dataMore Semantic