COMPSCI 732: Semantic Web Technologies

1
COMPSCI 732Semantic Web Technologies

• Semantic Web Architecture

2
Where are we?
Title
1 Introduction
2 Semantic Web Architecture
3 Resource Description Framework (RDF)
4 Web of Data
5 Generating Semantic Annotations
6 Storage and Querying
7 Web Ontology Language (OWL)
8 Rule Interchange Format (RIF)
3
Overview

• Introduction and motivation
• Technical solutions
• Semantic Web architecture
• Uniform Resource Identifier
• eXtensible Markup Language (XML)
• XML Schema
• Namespaces
• Extensions
• Illustration by a large example
• Summary
• References

4
INTRODUCTION AND MOTIVATION
5
A Semantic Web Scenario From Today

• Queries
• Which type of music is played by UK radio
  stations?
• Which UK radio station is playing titles by
  Swedish composers?
• Information to answer query is available on the
  Web
• Web search engines analyze Web content one page
  at a time
• The Semantic Web provides better framework to
  answer such queries
• combines data
• distributed across different sources, and
• described in machine-interpretable manner

6
Steps in Answering Queries

• Playlists of BBC radio shows published online in
  Semantic Web formats
• Music groups such as ABBA have an
  identifierhttp//www.bbc.co.uk/music/artists/d87
  e52c5-bb8d-4da8-b941-9f4928627dc8artist
• Identifier can relate music group to information
  at Musicbrainz
• Music community portal exposing data on Semantic
  Web
• http//musicbrainz.org
• Knows about band members (e.g. Benny Andersson)
• Aligns its information with Wikipedia
• Information on UK radio stations may be found in
  lists on Web pages
• Can be translated into similar Semantic Web
  representation

7
Describing Things and Their Relationships

• Meaning of Relationships, e.g., band memberships
  explained online, too
• Using collections of Ontologies available on the
  Web
• Dublin Core (general properties of information
  resources)
• http//dublincore.org/
• SKOS (covering taxonomic descriptions)
• http//www.w3.org/2004/02/skos/
• Specialized ontologies (covering the music
  domain)
• Data at the BBC currently use at least nine
  different ontologies
• http//www.bbc.co.uk/ontologies/programmes
• Availability of data in these formats enables
  queries to be answered
• Based on a query language

8
Towards the Required Infrastructure

• What infrastructure is required to implement the
  scenario from before?
• Generic software components, Languages, Protocols
• Their seamless interaction to satisfy requests
• Purpose of Lecture
• Investigate Semantic Web Architecture
• Analyze requirements from technical need to
  identify and relate data
• Analyze organizational needs to maintain Semantic
  Web as a whole

9
Web Architecture

• The Semantic Web is an evolution of the Web
• Important for the fast growth and adoption of the
  Web are
• Many people can set up Web servers easily and
  independently from each other
• More people can create documents, put them
  online, and link them to each other
• Even more people can browse and access any Web
  server to retrieve documents
• Web architecture allows graceful degradation of
  user experience when
• Network is partially slow (World Wide Wait),
  while other parts still operate at full speed
• Single Web servers break, because others still
  work
• Hyperlinks are broken, because other links still
  lead somewhere
• Separation of concerns justifies less quality
  outputs
• Users can easily create and access documents
• Distributed nature of system, without need of
  central coordinator, results in robustness

10
Web Architecture Principles

• Explicit simple data representation
• Common data representation hides underlying
  technologies (e.g. HTML)
• Distributed system
• Data sources without centralized instance
  controlling who owns what type of info
• Distributed ownership and control can facilitate
  adoption and scalability
• E.g. Web pages are under full control of their
  producers
• Cross-referencing
• Reuse of existing data and data definitions from
  different authorities (e.g. hyperlinks)
• Loose coupling achieved by common language layers
• Communication in standardized languages
• These must be easy to customize
• Overall communication must not be jeopardized by
  such specialization
• E.g. Coupling of Web clients/servers HTTP for
  transport, HTML for Web content
• Ease of publishing and consumption
• Easy publishing and consumption of simple data
• Comprehensive publishing and consumption of
  complex data, e.g.HTML simple to convey textual
  info powerful browsers/content management systems

11
Semantic Web Requirements and Examples

• Must be able to represent entities and their
  relationships (1)
• A person, the birthday of a person, the name of a
  person (Benny Andersson)
• Must be serializable in standardized manner to
  easily exchange data between different computing
  nodes (1,2,4)
• Ease of joining information from MusicBrainz,
  BBC, DBPedia
• Entities must be referable across borders of
  ownership or computing systems to allow for
  cross-linking of data (1,2,3,4)
• ABBAs Benny Andersson becomes hard to
  distinguish from other Benny Anderssons
• Expressive, machine-understandable data
  description language (1,4,5)
• Manual inspection not scalable refinements of
  basic model impossible
• BBC Data involves radio stations, shows, their
  versions, songs and their artists
• A query and manipulation language to select and
  aggregate data (5)
• The number of Swedish composers being broadcast
  on a specific program
• Reasoning desirable to facilitate querying (5)
• Direct relationship between a program and a song
  using inference
• Transport of data and query and their results by
  agreed-upon protocols (HTTP)
• May involve encrypted data requests and
  transports (HTTPs) signature of data items to
  ensure authenticity of user requests and control
  access to resources

12
Additional Requirements

• Core requirements not yet included in language
  architecture
• Versatile means for user interaction
• Broad accessibility requires viewing, searching,
  browsing, querying of data
• While at the same time abstracting from
  intricacies underlying their distributed origin
• On-the-fly data integration of multiple data
  sources assemble information from multitude of
  sources without a priori knowledge about domain
  or structure of data
• Facilitation of data production and publishing
  metadata creation and migration of data must be
  made convenient, independent from origin of data
• Provenance and Trust
• Authorship and ownership get lost during data
  processing and aggregation
• Origin, Reliability, Trustworthiness must be
  rethought to apply them for individual and
  aggregated data items, to establish faithful
  authentication at Semantic Web scale
• Alignment of unconnected sets of data
• Interlinking implies capability to suggest
  alignments between identifiers or concepts from
  different sets of data, beyond mere use of
  identifiers such as URI/IRIs
• Such alignment may be necessary to enable a real
  Web of Data

13
Semantic Web Architecture

• Formalized components and their relationships
• What technologies make up the Semantic Web
• What are the dependencies between components
• Roadmap for steps of developing the Semantic Web

14
TECHNICAL SOLUTION

• The Semantic Web architecture and its foundations

15
Search and Query the Web I

• The Web is a constantly growing network of
  distributed resources
• More than 1 trillion unique URLs
• More than 100 billion pages
• More than 200 million web sites
• Check most updated data on http//news.netcraft.c
  om/archives/web_server_survey.html
• User needs to be able to efficiently search
  resources/content over the Web
• When I Google Milan do I find info on the city
  or the soccer team?
• User needs to be able to perform query over
  largely distributed resources
• When is the next performance of the rock band
  U2, where it will be located, what are the best
  ways to reach the location, what are the
  attractions nearby

16
Search and Query the Web II

• On2Broker is the evolution of Ontobroker, a
  systems that aims at providing a solution to the
  problems discussed in the previous slides by
  adopting Semantic Technologies
• On2Broker is a system that processes distributed
  information sources and that provides intelligent
  information retrieval, query answering
• On2Broker relies on components of the Semantic
  Web Architecture
• D. Fensel, S. Decker, M. Erdmann, R. Studer
  Ontobroker in a Nutshell. ECDL 1998 663-664

17
On2Broker Architecture
18
On2Broker Components I

• Query Interface
• Provides a structured input that enables users to
  define their queries without any knowledge of the
  query language
• Input queries are then transformed to the query
  language (e.g. SparQL)
• Repository
• Decouples query answering, information retrieval
  and reasoning
• Provide support for materialization of inferred
  knowledge

19
On2Broker Components II

• Crawlers and Wrappers (or Info Agent)
• Extract knowledge from different distributed and
  heterogeneous data sources
• RDFa pages and RDF repositories can be included
  directly
• HTML and XML data sources require processing by
  wrappers to derive RDF data
• Inference Engine
• Relies on knowledge imported from the crawlers
  and axioms contained in the repository to support
  query answers
• Adopts Horn logic and closed world assumption

20
On2Broker Example

1. Tim Berners-Lee knows Christian Bizer and Tom
   Heath

1. Whom does Tim Berners-Lee know?
2. SELECT DISTINCT ?s ?o WHERE ?s foafknows
?o .

1. Extract RDF from http//www.w3.org/People/Berners
   -Lee/dblp

1. Extract RDF from fensel.comdblp

• Extends KBif x dblpcoauthor y then x
  foafknows y
• if y foafknows x then x foafknows y

21
SemWeb Architecture Requirements

• Extensibility
• Each layer should extend the previous one(s)
• Support for data interchange
• Using data from one source in other applications
• Support for ontology description with different
  complexity
• Including rules
• Support for data query
• Support for data provenance and trust evaluation

see the Semantic Web Roadmap http//www.w3.org/De
signIssues/Semantic.html
22
Semantic Web Stack
Rules RIF
Adapted from http//en.wikipedia.org/wiki/Semantic
_Web_Stack
23
UNICODE, URI and XML

• UNICODE is the standard international character
  set
• E.g. used to encode the data in the repository
• Uniform Resource Identifiers (URIs) identify
  things and concepts
• E.g. used to identify resources on the Web and in
  the repository
• Be aware to distinguish between information and
  non-information resources
• http//www.bbc.co.uk/music/artists/d87e52c5-bb8d-
  4da8-b941-9f4928627dc8artist vs.
  http//dbpedia.org/resource/ABBA
• Data publishers on the Semantic Web use Linked
  data principles
• Use URIs as names for things
• Use HTTP URIs so that people can look up those
  names
• When someone looks up a URI, provide useful
  information, using standards (RDF,SPARQL)
• Include links to other URIs, so that they can
  discover more things.
• eXtensible Markup Language (XML) used for data
  exchange
• Used on the Semantic Web to exchange the
  description of resources
• E.g. format that can be transformed into RDF and
  imported into the repository

24
RDF, RDFS and OWL

• Resource Description Framework (RDF)
• is the HTML of the Semantic Web
• Simple way to describe resources on the Web
• Based on triples ltsubject, predicate, objectgt
• Various serializations, including one based on
  XML
• A simple ontology language (RDFS)
• E.g. language used to store the data in the
  repository
• More in lecture 3
• Web Ontology Language (OWL)
• Is a more complex ontology language than RDFS
• Layered language based on Description Logics
• Overcomes some RDF(S) limitations
• E.g. ontology language used to define the schemas
  used in repository
• More in lecture 7

25
RDF Graph Encoding a Description of ABBA
26
RDF Serialized in RDF/XML

• lt?xml version1.0gt
• lt!DOCTYPE rdfRDF
• lt!ENTITY bbca http//www.bbc.co.uk/music/artists/
  gt
• lt!ENTITY bbci http//www.bbc.co.uk/music/images/a
  rtists/gt
• lt!ENTITY mba http//musicbrainz.org/artist/gtgt
• ltrdfRDF
• xmlnsrdfhttp//www.w3.org/1999/02/22-rdf-synta
  x-ns
• xmlnsowlhttp//www.w3.org/2002/07/owl
• xmlnsfoafhttp//xmlns.com/foaf/0.1/
• xmlnsmohttp//purl.org/ontology/mo/gt
• ltmoMusicArtist rdfabouthttp//www.bbc.co.uk/m
  usic/artists/d87e52c5-bb8d-4da8-b941-9f4928627dc8
  artistgt
• ltrdftype rdfresourcehttp//purl.org/ontology/
  mo/MusicGroup/gt
• ltfoafnamegtABBAlt/foafnamegt
• ltfoafhomepage rdfresourcehttp//www.abbasite.
  com//gt
• ltmoimage rdfresourcebbci542x305/d87e52c5-bb
  8d-4da8-b941-9f4928627dc8.jpggt
• ltmomember rdfresourcebbca042c35d3-0756-4804
  -b2c2-be57a683efa2artistgt
• ltmomember rdfresourcebbca2f031686-3f01-4f33
  -a4fc-fb3944532efaartistgt

27
RDF Serialized in Turtle

• _at_prefix rdf lthttp//www.w3.org/1999/02/22-rdf-sy
  ntax-nsgt .
• _at_prefix owl lthttp//www.w3.org/2002/07/owlgt .
• _at_prefix foaf lthttp//xmlns.com/foaf/0.1/gt .
• _at_prefix mo lthttp//purl.org/ontology/mo/gt .
• lthttp//www.bbc.co.uk/music/artists/d87e52c5-bb8d
  -4da8-b941-9f4928627dc8artistgt
• rdftype moMusicArtist, moMusicGroup
• foafname ABBA
• foafhomepage lthttp//www.abbasite.com/gt

28
RDFS and OWL Example

• Reasoning example in RDFS
• rdfssubClassOf can model class hierarchies
• moMusicGroup and moMusicArtist specify two
  classes
• Axiom ltmoMusicGroup, rdfssubClassOf,
  moMusicArtistgt
• Stating that ABBA is an instance of type
  MusicGroup enables reasoners to conclude that
  ABBA is also an instance of type MusicArtist
• When query asks for all MusicArtists, then ABBA
  will be contained in query result, even though
  there is no explicit assertion of this
• Reasoning example in OWL
• owlsameAs can be used to specify that two
  resources are identical
• To consolidate information about ABBA from
  multiple sources we can specify
  thathttp//www.bbc.co.uk/music/artists/d87e52c5
  -bb8d-4da8-b941-9f4928627dc8artist and
  http//dbpedia.org/resource/ABBA are the same

29
SPARQL and Rule Languages

• SPARQL
• Query language for RDF triples
• A protocol for querying RDF data over the Web
• E.g. language used to query the repository from
  the user interface
• Can also be used for Updates
• More in lecture 6
• Rule languages (esp. Rule Interchange Format RIF)
  
• W3C recommendation for exchanging rule sets
  between rule engines
• Extend ontology languages with proprietary axioms
• Based on different types of logics
• Description Logic
• Logic Programming
• E.g. used to enable reasoning over data to infer
  new knowledge
• More in lecture 8

30
SPARQL Example

• SPARQL query for other music groups that members
  of ABBA sing in
• PREFIX rdf lthttp//www.w3.org/1999/02/22-rdf-syn
  tax-nsgt
• PREFIX foaf lthttp//xmlns.com/foaf/0.1/gt
• PREFIX mo lthttp//purl.org/ontology/mo/gt
• SELECT ?memberName ?groupName
• WHERE
• lthttp//www.bbc.co.uk/music/artists/d87e52c5-bb8
  d-4da8-b941-9f4928627dc8artistgt
• momember ?m .
• ?x momember ?m .
• ?x rdftype moMusicGroup .
• ?m foafname ?memberName .
• ?x foafname ?groupName
• FILTER (?groupName ltgt ABBA)

31
SPARQL Example

• SPARQL query for other music groups that members
  of ABBA sing in
• Graphical representation of WHERE clause

lthttp//www.bbc.co.uk/music/artists/d87e52c5-bb8d
-4da8-b941-9f4928627dc8artistgt momember ?m
. ?x momember ?m . ?x rdftype moMusicGroup
. ?m foafname ?memberName . ?x foafname ?gro
upName
32
Two RIF rules for mapping FOAF predicates

• True statements in antecedent of rule mean true
  statements in its conclusion
• if ?x foaffirstName ?first
• foafsurname ?last
• then
• ?x foaffamily_name ?last
• foafgivenname ?first
• foafname funcstring-join(?first ?last)
• if ?x foafname ?name and
• predcontains(?name, )
• then
• ?x foaffirstName funcstrong-before(?name,
  )
• foafsurname funcstrong-after(?name, )
  

33
Logics, Proof and Trust

• Security and Encryption
• HTTPs provides data integrity and confidentiality
  when transmitting data and queries
• Digital signing of RDF graphs provides
  authenticity and non-repudiation
• Unifying logic
• Bring together the various ontology and rule
  languages
• Connect unlinked data to provide more meaning to
  data, and drive data integration
• E.g. identity management and alignment via
  http//sameas.org
• Proof
• Explanation of inference results, data provenance
• Trust
• Trust that the system performs correctly
• Trust that the system can explain what it is
  doing
• Network of trust for data sources and services
• Technology and user interface
• Many open problems, topics for future research

34
Foundations
Rules RIF
35
UNICODE

• More than a-z, A-Z

36
Character Sets

• ASCII 7 bit, 128 characters (a-z, A-Z, 0-9,
  punctuation)
• Extension code pages 128 chars (ß, Ä, ñ, ø, Š,
  etc.)
• Different systems, many different code pages
• ISO Latin 1, CP1252 Western languages (197 Å)
• ISO Latin 2, CP1250 East Europe (197 L)
• Code page is an interpretation, not a property of
  text
• Swedish programmer would have to write ä
  aÄiÜ'Ön' ü instead of ai'\n'
• Thus if we do not interpret correctly the code
  page, the result visualized will not be the
  expected one

37
UNICODE an unambiguous code

• We need a solution that can be unambiguously
  interpreted, i.e. whether a code corresponds to a
  single character and vice versa
• Thats why UNICODE was created!
• Å L Æ ?
• U0024 U00C5 U0139 U00C6 U03AE
• ? ? ? ? ?
• U0643 U215D U2665 U0416
  U0E0D

38
UNICODE

• ISO standard
• About 100,000 characters, space for 1,000,000
• Unique code points from U-0000 through U-FFFF to
  U-10FFFF
• Well-defined process for adding characters
• When dealing with any text, simply use UNICODE
• Character code charts http//www.unicode.org/char
  ts/
• See also
• http//www.tbray.org/talks/rubyconf2006.pdf
• http//tbray.org/ongoing/When/200x/2003/04/06/Unic
  ode

39
URI UNIFORM RESOURCE IDENTIFIERS

• How to identify things on the Web

40
Identifier, Resource, Representation
Taken from http//www.w3.org/TR/webarch/
41
URI, URN, URL

• A Uniform Resource Identifier (URI) is a string
  of characters used to identify a name or a
  resource on the Internet
• A URI can be a URL or a URN
• A Uniform Resource Name (URN) defines an item's
  identity
• the URN urnisbn0-395-36341-1 is a URI that
  specifies the identifier system, i.e.
  International Standard Book Number (ISBN), as
  well as the unique reference within that system
  and allows one to talk about a book, but doesn't
  suggest where and how to obtain an actual copy of
  it
• A Uniform Resource Locator (URL) provides a
  method for finding it
• the URL http//www.auckland.ac.nz identifies a
  resource (UoA's home page) and implies that a
  representation of that resource (such as the home
  page's current HTML code, as encoded characters)
  is obtainable via HTTP from a network host named
  www.auckland.ac.nz

42
URI Syntax

• Examples
• http//www.ietf.org/rfc/rfc3986.txt
• mailtoJohn.Doe_at_example.com
• newscomp.infosystems.www.servers.unix
• telnet//melvyl.ucop.edu/
• URI Syntax scheme //authority /path
  ?query fragid
• The scheme distinguishes different kinds of URIs
• Authority normally identifies a server
• Path normally identifies a directory and a file
• Query adds extra parameters
• Fragment ID identifies a secondary resource

43
URI Syntax contd

• Reserved characters (like /?_at_ )
• Many allowed characters
• Rest percent-encoded by UTF-8
• http//google.com/search?qtechnikerstraC39Fe
• IRI Internationalized Resource Identifier
• Allows whole UNICODE
• Specifies transformation into URI mostly UTF-8
  encoding

44
URI Schemes
Scheme Description RFC
file Host-specific file names 1738
ftp File Transfer Protocol 1738
http Hypertext Transfer Protocol 2616
https Hypertext Transfer Protocol Secure 2818
im Instant Messaging 3860
imap internet message access protocol 5092
ipp Internet Printing Protocol 3510
iris Internet Registry Information Service 3981
ldap Lightweight Directory Access Protocol 4516
mailto Electronic mail address 2368
mid message identifier 2392

• Schemes partition the URI space into subspaces
• Schemes can add or clarify properties of
  resources
• Ownership (how authorities are formed)
• Persistence (how stable the URIs should be)
• Protocol (default access protocol)

From http//www.iana.org/assignments/uri-schemes.h
tml
45
XML EXTENSIBLE MARKUP LANGUAGE

• How to exchange structured data on the Web

46
eXtensible Markup Language

• Language for creating languages
• Meta-language
• XHTML is a language HTML expressed in XML
• W3C Recommendation (standard)
• XML is, for the information industry, what the
  container is for international shipping
• For structured and semistructured data
• Main plus wide support, interoperability
• Platform-independent
• Applying new tools to old data

47
Structure of XML Documents

• Elements, attributes, content
• One root element in document
• Characters, child elements in content

48
XML Element

• Syntax ltnamegtcontentslt/namegt
• ltnamegt is called the opening tag
• lt/namegt is called the closing tag
• Examples
• ltgendergtFemalelt/gendergt
• ltstorygtOnce upon a time there was. lt/storygt
• Element names case-sensitive

49
Attributes to XML Elements

• Name/value pairs, part of element contents
• Syntax
• ltname attribute_name"attribute_value"gtcontentslt/n
  amegt
• Values surrounded by single or double quotes
• Example
• lttemperature unit"F"gt64lt/temperaturegt
• ltswearword language'fr'gtconlt/swearwordgt

50
Empty Elements

• Empty element ltnamegtlt/namegt
• This can be shortened ltname/gt
• Empty elements may have attributes
• Example
• ltgrade value'A'/gt

51
Comments

• May occur anywhere in element contents or outside
  the root element
• Start with lt!--
• End with --gt
• May not contain a double hyphen
• Comments cannot be nested
• Exampleltelementgtcontent lt!-- a comment, will
  be ignored in processing --gtlt/elementgtlt!--
  comment outside the root element --gt

52
Nesting Elements

• Elements may contain other (child) elements
• The containing element is the parent element
• Elements must be properly nested
• Example with improper nesting
• ltbgtbold ltigtbold-italiclt/bgt italic?lt/igt
• The above is not XML (not well-formed)

53
Special Characters in XML

• lt and gt are obviously reserved in content
• Written as lt and gt
• Same for ' and " in attribute values
• Written as apos and quot
• Now is also reserved
• Written as amp
• Any character 223 or xdf ? ß
• Decimal or hexa-decimal unicode code point
• Elements and attributes whose name starts with
  xmlare also special

54
Uses of XML

• Document mark-up XHTML
• HTML is a language, so it can be expressed in XML
• Exchanged data
• Scalable vector graphics SVG
• E-commerce ebXML
• Messaging in general SOAP
• And many more standards
• Internal data
• Databases
• Configuration files
• Etc.

55
Why XML?

• For semistructured data
• Loose but constrained structure
• Unspecified content length
• For structured data
• Table(s) or similar rows
• Well-defined structure, data types
• Good interoperability
• But requirements for quick access, processing

56
XML Parsers

• Document Object Model (DOM) builder
• Creates an object model of XML document,
  tree-traversal API
• In-memory representation, random access
• DOM complex, simpler JDOM etc.
• Simple API for XML parsing (SAX)
• Views XML as stream of events
• el_start("date"), attribute("day", "10"),
  el_end("date")
• Content reported as callback to methods on
  handler object of design
• DOM builder can use SAX
• Pull parsers
• Intermediate parsed results can be accessed as
  local variables
• StAX (JAVA), XMLReader (PHP), System.XML.XMLReader
  (.NET)

57
NAMESPACES

• How to distinguish categories of resources

58
The Problem

• Documents use different vocabularies
• Example 1 CD music collection
• Example 2 online order transaction
• Merging multiple documents together
• Name collisions can occur
• Example 1 albums have a ltnamegt
• Example 2 customers have a ltnamegt
• How do you differentiate between the two?

59
The Solution Namespaces!

• What is a namespace?
• A syntactic way to differentiate similar names in
  an XML document
• Binding namespaces
• Uses Uniform Resource Identifier (URI)
• e.g. http//example.com/NS
• Can bind to a named or default prefix

60
Namespace Binding Syntax

• Use xmlns attribute
• Named prefix
• ltafoo xmlnsahttp//example.com/NS/gt
• Default prefix
• ltfoo xmlnshttp//example.com/NS/gt
• Element and attribute names are qualified
• URI, local part (or local name) pair
• e.g. http//example.com/NS , foo

61
Example Document I

• Namespace binding
• lt?xml version1.0 encodingUTF-8?gt
• ltordergt
• ltitem codeBK123gt
• ltnamegtCare and Feeding of Wombatslt/namegt
• ltdesc xmlnshtmlhttp//www.w3.org/1999/xhtmlgt
  
• The lthtmlbgtbestlt/htmlbgt book ever written!
• lt/descgt
• lt/itemgt
• lt/ordergt

62
Example Document II

• Namespace scope
• lt?xml version1.0 encodingUTF-8?gt
• ltordergt
• ltitem codeBK123gt
• ltnamegtCare and Feeding of Wombatslt/namegt
• ltdesc xmlnshtmlhttp//www.w3.org/1999/xhtmlgt
  
• The lthtmlbgtbestlt/htmlbgt book ever written!
• lt/descgt
• lt/itemgt
• lt/ordergt

63
Example Document III

• Bound elements
• lt?xml version1.0 encodingUTF-8?gt
• ltordergt
• ltitem codeBK123gt
• ltnamegtCare and Feeding of Wombatslt/namegt
• ltdesc xmlnshtmlhttp//www.w3.org/1999/xhtmlgt
  
• The lthtmlbgtbestlt/htmlbgt book ever written!
• lt/descgt
• lt/itemgt
• lt/ordergt

64
XML SCHEMA

• How to define XML document structures

65
What is it?

• A grammar definition language
• More expressive than Document Type Definitions
  (DTDs)
• Uses XML syntax
• Defined by W3C
• Primary features
• Datatypes
• e.g. integer, float, date, etc
• More powerful content models
• e.g. namespace-aware, type derivation, etc

66
XML Schema Types

• Simple types
• Basic datatypes
• Can be used for attributes and element text
• Extendable
• Complex types
• Defines structure of elements
• Extendable
• Types can be named or anonymous

67
Simple Types

• DTD datatypes
• Strings, ID/IDREF, NMTOKEN, etc
• Numbers
• Integer, long, float, double, etc
• Other
• Binary (base64, hex)
• QName, URI, date/time
• etc

68
Deriving Simple Types

• Apply facets
• Specify enumerated values
• Add restrictions to data
• Restrict lexical space
• Allowed length, pattern, etc
• Restrict value space
• Minimum/maximum values, etc
• Extend by list or union

69
A Simple Type Example

• Integer with value (1234, 5678
• ltxsdsimpleType nameMyIntegergt
• ltxsdrestriction basexsdintegergt
• ltxsdminExclusive value1234/gt
• ltxsdmaxInclusive value5678/gt
• lt/xsdrestrictiongt
• lt/xsdsimpleTypegt

70
A Simple Type Example II

• Validating integer with value (1234, 5678
• ltdata xsitype'MyInteger'gtlt/datagt INVALID
• ltdata xsitype'MyInteger'gtAndylt/datagt INVALID
• ltdata xsitype'MyInteger'gt-32lt/datagt INVALID
• ltdata xsitype'MyInteger'gt1233lt/datagt INVALID
• ltdata xsitype'MyInteger'gt1234lt/datagt INVALID
• ltdata xsitype'MyInteger'gt1235lt/datagt
• ltdata xsitype'MyInteger'gt5678lt/datagt
• ltdata xsitype'MyInteger'gt5679lt/datagt INVALID

71
Complex Types

• Element content models
• Simple
• Mixed
• Unlike DTDs, elements in mixed content can be
  ordered
• Sequences and choices
• Can contain nested sequences and choices
• All
• All elements required but order is not important

72
A Complex Type Example I

• Mixed content that allows ltbgt, ltigt, and ltugt
• ltxsdcomplexType nameRichText mixedtruegt
• ltxsdchoice minOccurs0 maxOccursunboundedgt
• ltxsdelement nameb typeRichText/gt
• ltxsdelement namei typeRichText/gt
• ltxsdelement nameu typeRichText/gt
• lt/xsdchoicegt
• lt/xsdcomplexTypegt

73
A Complex Type Example II

• Validation of RichText
• ltcontent xsitype'RichText'gtlt/contentgt
• ltcontent xsitype'RichText'gtAndylt/contentgt
• ltcontent xsitype'RichText'gtXML is
  ltigtawesomelt/igt.lt/contentgt
• ltcontent xsitype'RichText'gtltBgtboldlt/Bgtlt/contentgt
  INVALID
• ltcontent xsitype'RichText'gtltfoo/gtlt/contentgt
  INVALID

74
EXTENSIONS
75
Building On The Foundations

• RDF for semantic data
• Graphs of linked data
• Semantic Web
• Any XML or HTML can support translation to RDF
• GRDDL a pointer to a transformation
• RDFa RDF in XHTML
• Makes existing data part of the Semantic Web
• XML has encryption and digital signature
• Necessary technologies for data provenance, trust

76
Web of Linked Data
77
RDF Teaser

• Resource Description Framework
• Metadata about Web resources
• But also any other data
• Graphs of resources interlinked with properties
• Rafael Nadal plays Tennis
• knows Shakira
• Shakira sings Waka waka
• Ontology languages for data schemas
• Various properties knows, plays, sings
• Classes of resources Person, Athlete, Singer,
  Sport, Song
• SPARQL for querying the data

78
ILLUSTRATION BY A LARGER EXAMPLE

• The Semantic Web architecture in practice

79
Semantic Conference

• All the data about the conference is part of the
  Semantic Web
• Date, location
• Organizers, peer-review committees
• Articles (papers), their authors
• Detailed program schedule
• Each Semantic Web architecture layer plays a
  role
• ISWC is annotating conference data usingSemantic
  Web technologies
• http//data.semanticweb.org/conference/iswc/2011/h
  tml
• Currently available data regards only papers and
  authors
• This could be extended to support features
  discussed above

80
Foundation Layers

• UNICODE
• All participants' names should be in UNICODE
  because they are international Denny Vrandecic,
  Diego Meroño, François Maué
• Same for paper titles "a-decay and ß-decay of
  heavy atoms"
• URI All important things must have identifiers,
  for example
• Conference http//data.semanticweb.org/conference
  /iswc/2011
• Participant http//data.semanticweb.org/person/pi
  ero-bonatti
• Participant's affiliation http//data.semanticweb
  .org/organization/talis-information-limited
• Paper http//data.semanticweb.org/conference/iswc
  /2011/paper/tutorial/7

81
Data Layers

• XML
• The HTML pages should be in XHTML
• The RDF data (below) should be in RDF/XML
• News feed should be in Atom (an XML format)
• RDF
• The conference dataset, and any useful subsets,
  should be published in RDF for download for
  example
• http//data.semanticweb.org/conference/iswc/2011/r
  df

82
Ontologies, Query

• RDFS, OWL
• The conference would use various vocabularies and
  ontologies, such as
• FOAF (Friend of a friend) for talking about the
  attendees and authors/presenters
• Dublin Core for paper metadata
• Calendar ontology for the program
• SPARQL
• The conference server should have a public SPARQL
  endpoint that can be used for queries over the
  conference data
• http//data.semanticweb.org/snorql/

83
Browsing ISWC Data
http//data.semanticweb.org/person/tom-heath/html
84
Querying ISWC Data
http//data.semanticweb.org/snorql/
85
SUMMARY

• Thats almost all for today

86
Things to Keep in Mind

• Semantic Web builds on the Web
• For any text, use UNICODE, probably UTF-8
• URIs can identify anything
• Not only documents on the Web
• XML helps with data exchange, interoperability
• XML languages are distinguished with namespaces

87
References

• Mandatory
• http//www.w3.org/TR/webarch/
• http//www.w3.org/DesignIssues/Architecture.html
• Further reading
• http//www.w3.org/Provider/Style/URI
• http//www.ietf.org/rfc/rfc3986.txt
• http//www.unicode.org/charts/
• http//www.tbray.org/talks/rubyconf2006.pdf
• http//tbray.org/ongoing/When/200x/2003/04/06/Unic
  ode
• http//www.w3.org/TR/xml/
• http//www.w3.org/TR/xml-names/
• http//www.w3.org/TR/xmlschema-1/
• Fensel et al., On2broker Semantic-Based Access
  to Information Sources at
• the WWW
• Fensel et al. Ontobroker in a Nutshell
• http//www.ics.uci.edu/fielding/pubs/dissertation
  /top.htm
• http//www.w3.org/DesignIssues/Semantic.html

88
References

• Wikipedia links
• http//en.wikipedia.org/wiki/Semantic_Web_Stack
• http//en.wikipedia.org/wiki/URI
• http//en.wikipedia.org/wiki/Unicode
• http//en.wikipedia.org/wiki/XML
• http//en.wikipedia.org/wiki/XML_Namespaces
• http//en.wikipedia.org/wiki/Resource_Description_
  Framework
• http//en.wikipedia.org/wiki/RDF_Schema
• http//en.wikipedia.org/wiki/Web_Ontology_Language
  
• http//en.wikipedia.org/wiki/SPARQL
• http//en.wikipedia.org/wiki/Rule_Interchange_Form
  at

89
Next Lecture
Title
1 Introduction
2 Semantic Web Architecture
3 Resource Description Framework (RDF)
4 Web of Data
5 Generating Semantic Annotations
6 Storage and Querying
7 Web Ontology Language (OWL)
8 Rule Interchange Format (RIF)
90
Questions?
90