Semantic Markup Languages: A Gentle Introduction Yolanda Gil USC/Information Sciences Institute [e-mail]

1
Semantic Markup LanguagesA Gentle
IntroductionYolanda GilUSC/Information
Sciences Institutegil_at_isi.edu
2
Outline

• I The Big Picture
• The Semantic Web
• http//www.scientificamerican.com/2001/0501issue/0
  501berners-lee.html
• http//www.w3.org/DesignIssues/Semantic.html
• II A Gentle Introduction
• XSD, RDFS, DAML
• http//trellis.semanticweb.org/expect/web/semantic
  web/comparison.html
• III The Big Picture Revisited
• W3Cs Semantic Web principles
• http//www.semanticweb.org
• How this is changing our research in Knowledge
  Bases
• http//www.isi.edu/expect/papers/gil-seweb-book-01
  .pdf

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I THE BIG PICTURE
4
The Semantic Web

• W3Cs Tim Berners-Lee Weaving the Web
• I have a dream for the Web and it has two
  parts.
• The first Web enables communication between
  people
• The Web shows how computers and networks enable
  the information space while getting out of the
  way
• The new Web will bring computers into the action
• Step 1 -- Describe putting data on the Web in
  machine-understandable form -- a Semantic Web
• RDF (based on XML)
• Master list of terms used in a document (RDF
  schema)
• Each document mixes global standards and local
  agreed-upon terms (namespaces)
• Step 2 -- Infer and reason apply logic inference
• Operate on partial understanding
• Answering why
• Heuristics

5
Semantics and Meaning according to TBL

• In the extreme view, the world can be seen as
  only connections, nothing else. I like the
  idea that a piece of information is really
  defined only by what its related to, and how
  its related. There really is little else to
  meaning. The structure is everything.
• What matters is in the connections. It isnt
  the letters, its the way they are strung
  together into words. into phrases. into
  a document.
• For the people, by the people the right to link
• Once something was made available, it
  should be accesible to anyone . And it should
  be possible to make a link to that thing.

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And There You Have It
?
SMIL
PICS
XSD
XLink
?
?
XML
XPath
DAML
RDF
?
XSLT
RDF(S)
OIL
RSS
DAMLOIL
N3
?
?
DAML-S
?
CYCL
KIF
WSDL
MELD
LOOM
XQUERY
OKBC
FOL
XTM
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II THE GENTLE INTRODUCTION
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The Layer Cake TBL,XML2000
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The Layer Cake TBL,XML2000
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URIs Uniform Resource Identifiers (aka URLs)

• http//trellis.semanticweb.org/semanticweb/slides/
  
• ftp//www.allinone.org/all.gz
• The Web is an information space. URIs are the
  points in that space.
• Short strings that identify resources in the web
  documents, images, downloadable files, services,
  electronic mailboxes, and other resources.
• They make resources addressable in the same
  simple way. They reduce the tedium of "log in to
  this server, then issue this magic command ..."
  down to a single click.

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Unicode

• A character encoding system, like ASCII,
  designed to help developers who want to create
  software applications that work in any language
  in the world
• Unicode provides a unique number for every
  character, no matter what the platform, no matter
  what the program, no matter what the language

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The Layer Cake TBL,XML2000
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Why XML (eXtensible Markup Language)

• Problems with HTML
• HTML design
• - HTML is intended for presentation of
  information as
• Web pages.
• - HTML contains a fixed set of markup
  tags.
• This design is not appropriate for data
• - Tags dont convey meaning of the data
  inside the tags.
• - Tags are not extensible.

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The Design of XML

• Tags can be used to represent the meaning of
  data/information
• separates syntax (structural representation) from
  semantics gt only syntax is considered in XML
• There is no fixed set of markup tags - new tags
  can be defined
• Underlying data model is a tree structure
• XML is the new ASCII -- Tim Bray
• http//www.w3.org/TR/2000/REC-xml-20001006

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Simple XML Example
Make up your own tags
ltBookstoregt ltBook ID101gt ltAuthorgtJohn
Doelt/Authorgt ltTitlegtIntroduction to
XMLlt/Titlegt ltDategt12 June 2001lt/Dategt
ltISBNgt121232323lt/ISBNgt ltPublishergtXYZlt/Publishe
rgt lt/Bookgt ltBook ID102gt ltAuthorgtFoo
Barlt/Authorgt ltTitlegtIntroduction to
XSLlt/Titlegt ltDategt12 June 2001lt/Dategt
ltISBNgt12323573lt/ISBNgt ltPublishergtABClt/Publisher
gt lt/Bookgt lt/Bookstoregt
Sub-elements
XML by itself is just hierarchically structured
text
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XSD XML Schema Definition

• Written in the same syntax as XML documents
  (unlike XML DTDs!)
• Elements and attributes
• Enhanced set of primitve datatypes.
• Wide range of primitive data types, supporting
  those found in databases (string, boolean,
  decimal, integer, date, etc.)
• Can create your own datatypes (complexType)
• - Can derive new type definitions on the
  basis of old ones (refinement)
• Can have constraints on attributes
• Examples maxlength, precision, enumeration,
  maxInclusive (upper bound), minInclusive (lower
  bound), etc.

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An important diversion Namespaces

• What is a Namespace ?
• The Namespace of an element, is the scope within
  which, it (and thus its name) is valid. (Ex. A
  basic block in C)
• Why do we need Namespaces ?
• If elements were defined within a global scope,
  it becomes a problem when combining elements from
  multiple documents.  Name collision is hard to
  avoid.
• Modularity If a markup vocabulary exists which
  is well understood and for which there is useful
  software available, it is better to reuse this
  rather than make it again.
• Namespaces in XML
• An XML namespace is a collection of names,
  identified by a URI reference.
• Names from XML namespaces may appear as
  qualified names, which contain a single colon,
  separating the name into a prefix and a local
  part. The prefix, which is mapped to a URI
  reference, selects a namespace

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XSD (XML Schema) Example
lt?xml version"1.0"?gt ltxsdschema
xmlnsxsdhttp//www.w3.org/2001/XMLSchema
targetNamespace"http//www.books
.org" xmlnshttp//www.book
s.orggt ltxsdelement
name"Bookstore"gt ltxsdcomplexTypegt
ltxsdsequencegt
ltxsdelement ref"Book" minOccurs"1"
maxOccurs"unbounded"/gt
lt/xsdsequencegt lt/xsdcomplexTypegt
lt/xsdelementgt ltxsdelement name"Book"gt
ltxsdcomplexTypegt ltxsdsequencegt
ltxsdelement ref"Title"
minOccurs"1" maxOccurs"1"/gt
ltxsdelement ref"Author" minOccurs"1"
maxOccursunbounded/gt
ltxsdelement ref"Date" minOccurs"1"
maxOccurs"1"/gt ltxsdelement
ref"ISBN" minOccurs"1" maxOccurs"1"/gt
ltxsdelement ref"Publisher" minOccurs"1"
maxOccurs"1"/gt lt/xsdsequencegt
lt/xsdcomplexTypegt lt/xsdelementgt
ltxsdelement name"Title" type"xsdstring"/gt
ltxsdelement name"Author" type"xsdstring"/gt
ltxsdelement name"Date" type"xsdDate"/gt
ltxsdelement name"ISBN" type"xsdinteger"/gt
ltxsdelement name"Publisher" type"xsdstring"/gt
lt/xsdschemagt
Prefix xsd refers to the XMLSchema namespace
xmlns refers to the default namespace
Defining the element Bookstore as a complex
Type
Containing a sequence of 1 or more Book
elements
When referring to another Element, use ref
The Author can be 1 or more
Element definitions
Notice the use of more meaningful data types
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XSL XML Stylesheet Language
An Example
lt?xml version'1.0'?gt ltxslstylesheet
xmlnsxsl"http//www.w3.org/TR/WD-xsl"gt
ltxsltemplate match"/"gt lthtmlgt ltbodygt
lttable cellpadding"2" cellspacing"0"
border"1" bgcolor"FFFFD5"gt lttrgt
ltthgtTitlelt/thgt
ltthgtAuthorlt/thgt ltthgtDatelt/thgt
ltthgtISBNlt/thgt lt/trgt
ltxslfor-each select"Bookstore/Book"gt
lttrgtlttdgtltxslvalue-of select"Title"/gtlt/tdgt
lttdgtltxslvalue-of select"Author"/gtlt/
tdgt lttdgtltxslvalue-of
select"Date"/gtlt/tdgt
lttdgtltxslvalue-of select"ISBN"/gtlt/tdgt
lt/trgt lt/xslfor-eachgt lt/tablegt
lt/bodygt lt/htmlgt lt/xsltemplategt
lt/xslstylesheetgt
xsl namespace
Match the Root Element
Go through Each Book Element (inside a
Bookstore Element)
What you print out when the root element matches
And, print out their Title, Author, Date, and ISBN
Result (Notice, that some fields have been
filtered out from the XML file)
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XML Tools/Software
XML Spy By far, the most comprehensive editor.
Handles XML files, DTDs, XSL files, as well as
XSD (XML Schema). Unfortunately only a 30 day
trial version. http//www.xmlspy.com/download.html
XML Notepad Microsoft XML Notepad is a simple
application for building and editing small sets
of XML-based data. Freeware. http//msdn.microsoft
.com/xml/notepad/download.asp XML Pro XML Pro is
a top-notch XML editor but it doesnt include as
many features as XML Spy. Shareware. http//www.ve
rvet.com/demo.html You can also validate your
XML files by just opening them with IE5.0 or
above. It checks if the XML file is well-formed
or not, and also validates against a DTD (if
specified on the DOCTYPE declaration Some nice
short Tutorials on XML/XSL/DTD/XML Schemas can be
found at www.w3schools.com
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Summary of the XML NS XSD LayerThe Power of
Simplicity

• Keeps the principles of SGML in place but its
  spec is thin enough to wave ?
• When I designed HTML, I chose to avoid giving it
  more power than it absolutely needed a
  principle of least power, which I have stuck to
  ever since. I could have used a language like
  Knuths Tex but -- TBL
• To say you are Using XML is sort of like saying
  you are using ASCII
• Using XSD (XML Schema) makes a lot more sense

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The Layer Cake TBL,XML2000
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Where XML XML Schemas Fail

• No semantics!
• Will XML scale in the metadata world?
• The order in which elements appear in an XML
  document is often meaningful. This seems highly
  unnatural in the metadata world.
• Furthermore, maintaining the correct order of
  millions of data items is impractical.
• XML allows constructions that mix up some text
  along with child elements, which are hard to
  handle.
• Ex.

ltbookgt lttitlegt lt/titlegt ltauthorgt
lt/authorgt ltisbngt lt/isbngt lt/bookgt
ltbookstoregt ltbookgt lt/bookgt ltbookgt
lt/bookgt lt/bookstoregt
lttopelemgtThis is some character string data
ltelemgt this is a child
ltsubelemgtthis is another childlt/subelemgt
lt/elemgt lt/topelemgt
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RDF (Resource Description Framework)

• RDF provides a way of describing resources via
  metadata (data about data)
• It restricts the description of resources to
  triplets (subject,predicate,object)
• It provides interoperability between applications
  that exchange machine
• understandable information on the Web.
• The broad goal of RDF is to define a mechanism
  for describing resources
• that makes no assumptions about a particular
  application domain,
• nor defines (a priori) the semantics of any
  application domain.
• Uses XML as the interchange syntax.
• Provides a lightweight ontology system.
• The formal specification of RDF is available at
• http//www.w3.org/TR/REC-rdf-syntax/

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RDF Syntax

• Subject, Predicate and Object Triplets (Tuples)
• Subject The resource being described.
• Predicate A property of the resource
• Object The value of the property
• A combination of them is said to be a Statement
  (or a rule)

John Doe
http//foo.bar.org/index.html
Author
A property of the web page (author) Predicate
A web page being described Subject
The value of the predicate (here the
author) Object
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RDF Example
lt?xml version"1.0"?gt ltrdfRDF
xmlnsrdf"http//www.w3.org/TR/WD-rdf-syntax"
xmlnss"http//description.org/schema/"gt
ltrdfDescription about"http//foo.bar.org/index
.html"gt ltsAuthorgtJohn Doelt/sAuthorgt
lt/rdfDescriptiongt lt/rdfRDFgt
Namespace for the RDF spec
Namespace s, a custom namespace
Subject
Author (property of the subject) (Also a resource)
Object. Can also point to a resource
The above statement says The Author of
http//foo.bar.org/index.html is John Doe
In this way, we can have different objects
(resources) pointing to other objects
(resources) , thus forming a DLG (Directed Line
Graph) You can also make statements about
statements reification Ex xyz says that
The Author of http//foo.bar.org/index.html is
John Doe
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RDF Schema

• A schema defines the terms that will be used in
  the RDF statements and gives specific meanings to
  them.
• http//www.w3.org/TR/rdf-schema/
• Example

ltrdfRDF xmllang"en" xmlnsrdf"http//www.w3
.org/1999/02/22-rdf-syntax-ns"
xmlnsrdfs"http//www.w3.org/2000/01/rdf-schema"
gt ltrdfDescription ID"MotorVehicle"gt ltrdftype
resource"http//www.w3.org/2000/01/rdf-schemaCla
ss"/gt ltrdfssubClassOf rdfresource"http//www
.w3.org/2000/01/rdf-schemaResource"/gt lt/rdfDescr
iptiongt ltrdfDescription ID"PassengerVehicle"gt
ltrdftype resource"http//www.w3.org/2000/01/rdf-
schemaClass"/gt ltrdfssubClassOf
rdfresource"MotorVehicle"/gt lt/rdfDescriptiongt
ltrdfDescription ID"Truck"gt ltrdftype
resource"http//www.w3.org/2000/01/rdf-schemaCla
ss"/gt ltrdfssubClassOf rdfresource"MotorVehicl
e"/gt lt/rdfDescriptiongt
RDF Schema Namespace
An ID attribute actually defines a new resource
Resource is the top level class
PassengerVehicle is a subclass of MotorVehicle
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Example (cont..)
ltrdfDescription ID"Van"gt ltrdftype
resource"http//www.w3.org/2000/01/rdf-schemaCla
ss"/gt ltrdfssubClassOf rdfresource"MotorVehicl
e"/gt lt/rdfDescriptiongt ltrdfDescription
ID"MiniVan"gt ltrdftype resource"http//www.w3.o
rg/2000/01/rdf-schemaClass"/gt ltrdfssubClassOf
rdfresource"Van"/gt ltrdfssubClassOf
rdfresource"PassengerVehicle"/gt lt/rdfDescripti
ongt ltrdfDescription ID"registeredTo"gt
ltrdftype resource"http//www.w3.org/1999/02/22-r
df-syntax-nsProperty"/gt ltrdfsdomain
rdfresource"MotorVehicle"/gt ltrdfsrange
rdfresource"Person"/gt lt/rdfDescriptiongt ltrdf
Description ID"rearSeatLegRoom"gt ltrdftype
resource"http//www.w3.org/1999/02/22-rdf-syntax-
nsProperty"/gt ltrdfsdomain rdfresource"Passen
gerVehicle"/gt ltrdfsdomain rdfresource"Minivan
"/gt ltrdfsrange rdfresource"http//www.w3.org/2
000/03/example/classesNumber"/gt lt/rdfDescription
gt lt/rdfRDFgt
Multiple Inheritance
Domain of a property
Range of a property
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RDF Tools/Resources
SirPAC A Simple RDF Parser Compiler. It parses
the RDF, and validates it. It also generates the
tuples and even draws a graph of the data
model. www.w3.org/RDF/Implementations/SiRPAC/
Reggie A Nice Metadata Editor. Java based
simple user interface to describe a web
resource. Can mail the metadata file to yourself
after finished editing. http//metadata.net/dstc/
Protégé Editor of ontologies in practically any
language you care about. Open source. http//www.
smi.stanford.edu/projects/protege/
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Summary RDF RDF Schema layer

• Minimalist model - (thing), Class, Property
• Subproperty, Subclass
• Domain Range
• Still not a W3C recommendation
• Continues to change
• Other languages are being built on XML substrate
  XQUERY, XTM

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The Layer Cake TBL,XML2000
34
Limitations of RDF
- Cannot define properties of properties
(unique, transitive) - No equivalence,
disjointness, etc. - No mechanism of specifying
necessary and sufficient conditions for class
membership. Example If it is given
that XYZ has a car which is 7ft high, has
wide wheels and loading space is 4 cub.m,
then we should be able to reason that
XYZ has an SUV, as given by the
necessary and sufficient conditions for being an
SUV height gt 4ft wide wheels
loading space gt 2 cub.m
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DAMLOILs History

• W3Cs Semantic Web Activity
• - RDF and metadata markup efforts to
  represent data in
• a machine understandable form.
• DARPA started the DARPA Agent Markup Language
  (DAML)
• program.
• possibly with ARPANET -gt Internet in mind
• EC (European Commission) funding programs
• - Ontology Interchange Language (OIL)
• - logic based language.
• - brings logic and inference to the
  Semantic Web
• www.daml.org
• DAMLOIL http//www.daml.org/2001/03/daml
  oil-index.html

36
DAMLOIL (www.daml.org)

• It builds on earlier W3C standards such as RDF
  and RDF Schema.
• DAML extends RDF and RDFS with richer modelling
  primitives.
• disjointWith, intersectionOf, oneOf, cardinality
• Able to provide properties of properties
• uniqueness, transitivity, etc.
• Current version DAMLOIL provides a semantic
  interpretation (model-theoretic semantics)
• http//www.daml.org/2001/03/damloil-index.html
  

37
An Example (from www.daml.org)
ltrdfRDF xmlnsrdf "http//www.w3.org/1999/02/2
2-rdf-syntax-ns" xmlnsrdfs"http//www.w3.org/
2000/01/rdf-schema" xmlnsdaml"http//www.daml
.org/2000/12/damloil" xmlns
"http//www.daml.org/2000/12/damloil-ex" gt ltda
mlOntology aboutgt ltdamlversionInfogtAn
example ontologylt/damlversionInfogt ltrdfsClass
rdfID"Animal"gt ltrdfslabelgtAnimallt/rdfslabelgt
ltrdfscommentgt This class of animals is
illustrative of a number of ontological idioms.
lt/rdfscommentgt lt/rdfsClassgt ltrdfsClass
rdfID"Male"gt ltrdfssubClassOf
rdfresource"Animal"/gt lt/rdfsClassgt ltrdfsClas
s rdfID"Female"gt ltrdfssubClassOf
rdfresource"Animal"/gt ltdamldisjointWith
rdfresource"Male"/gt lt/rdfsClassgt ltrdfsClass
rdfID"Man"gt ltrdfssubClassOf
rdfresource"Person"/gt ltrdfssubClassOf
rdfresource"Male"/gt lt/rdfsClassgt
Start of an ontology (about implies this
document)
The label is not used for logical interpretation
Can explicitly specify the set of Females to be
disjoint with the set of Males
The Person class is defined later
To be read conjunctively. A man is a sub-class of
Person and a Male
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Example (contd..)
ltrdfsClass rdfID"Woman"gt ltrdfssubClassOf
rdfresource"Person"/gt ltrdfssubClassOf
rdfresource"Female"/gt lt/rdfsClassgt ltrdfObjec
tProperty rdfID"hasParent"gt ltrdfsdomain
rdfresource"Animal"/gt ltrdfsrange
rdfresource"Animal"/gt lt/rdfObjectPropertygt ltr
dfObjectProperty rdfID"hasFather"gt
ltrdfssubPropertyOf rdfresource"hasParent"/gt
ltrdfsrange rdfresource"Male"/gt lt/rdfObjectPro
pertygt ltdamlDatatypeProperty rdfID"age"gt
ltrdfsrange rdfresource"http//www.w3.org/2000/1
0/XMLSchemanonNegativeInteger"/gt lt/damlDatatypeP
roperty ltrdfsClass rdfID"Person"gt
ltrdfssubClassOf rdfresource"Animal"/gt
ltrdfssubClassOfgt ltdamlRestrictiongt
ltdamlonProperty rdfresource"hasParent"/gt
ltdamltoClass rdfresource"Person"/gt
lt/damlRestrictiongt lt/rdfssubClassOfgt
ltrdfssubClassOfgt ltdamlRestriction
damlcardinality"1"gt ltdamlonProperty
rdfresource"hasFather"/gt
lt/damlRestrictiongt lt/rdfssubClassOfgt lt/rdfsCl
assgt
An objectProperty relates objects to objects
Describes the element which encloses this Property
Describes the value of the Property
Note Contrary to RDF, DAML takes the
intersection of the domains/ranges if
multiple domains/ranges are specified
A datatype property relates an object to a
primitive datatype value
The XML Schema datatype is referenced here
The Restriction defines an anonymous class of all
things that satisfy the restriction.
Restrictions on the property hasParent (only for
the Person class Local scope, as opposed to
rdfsrange) A person can have only another Person
as its parent
A Person can have only 1 Father
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Example (contd..)
Addition to the Animal Class without modifying it
-- about
ltrdfsClass rdfabout"Animal"gt ltrdfssubClassOfgt
ltdamlRestriction damlcardinality"2"gt
ltdamlonProperty rdfresource"hasParent"/gt
lt/damlRestrictiongt lt/rdfssubClassOfgt lt/rdfsCl
assgt ltrdfsClass rdfabout"Person"gt
ltrdfssubClassOfgt ltdamlRestriction
damlmaxcardinality"1"gt ltdamlonProperty
rdfresource"hasSpouse"/gt
lt/damlRestrictiongt lt/rdfssubClassOfgt lt/rdfsCl
assgt
Restrictions on the property hasParent An animal
can have exactly 2 parents
Restrictions on the property hasSpouse A person
can have only 1 spouse
Further constructs that the example doesnt use
Properties TransitiveProperty
(hasAncestor), UniqueProperty (hasMother),
inverseOf(hasChild -gt hasParent), etc. Classes
intersectionOf (a damlcollection), unionOf (a
damlcollection), sameClassAs,
complementOf, etc.
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DAML References/Tools
DAML Viewer It provides a means to view the
instances found in a DAML document.
http//www.daml.org/viewer/applet.html DAML
Crawler Results A list of .daml files on the
internet http//www.daml.org/crawler/pages.html
A DAML Validator http//www.daml.org/validator/
A DAML example explained It has the same
example as in the slides, discussed in
detail. http//www.daml.org/2001/03/damloil-walkt
hru.html
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42
The Layer Cake TBL,XML2000
43
The Layer Cake
DAMLOIL
WSDL
OIL
DAML-O
NOTATION 3
RDFS
XTM
XQUERY
XHTML
RDF
XML
HTML
44
To Learn More About These Languages...

• http//trellis.semanticweb.org/ more detailed
  tutorial slides
• http//trellis.semanticweb.org/expect/web/semantic
  web/flairs02.pdf
• http//trellis.semanticweb.org/expect/web/semantic
  web/comparison.html

45
The View from W3Chttp//www.w3.org/TR/

• XML Schema Part 0 Primer
• 02 May 2001, David C. Fallside
• XML Schema Part 1 Structures
• 02 May 2001, Henry S. Thompson, David Beech,
  Murray Maloney, N. Mendelsohn
• XML Schema Part 2 Datatypes
• 02 May 2001, Paul V. Biron, Ashok Malhotra
• Extensible Markup Language (XML) 1.0 (Second
  Edition)
• 6 October 2000, Tim Bray, Jean Paoli, C. M.
  Sperberg-McQueen, Eve Maler
• Namespaces in XML
• 14 January 1999, Tim Bray, Dave Hollander,
  Andrew
• Resource Description Framework (RDF) Model and
  Syntax Specification
• 22 February 1999, Ora Lassila, Ralph
  R. Swick
• Resource Description Framework (RDF) Schemas
• 3 March 2000, Dan Brickley, R.V. Guha
• RDF Model Theory
• 25 September 2001, Patrick Hayes
• XML Schema Formal Description

RECOMMENDATIONS
CAND REC
WORKING DRAFTS
46
W3C Review Stages

1. A Working Draft represents work in progress and a
   commitment by W3C to pursue work in this area. A
   Working Draft does not imply consensus by a group
   or W3C. A Candidate Recommendation is work that
   has received significant review from its
   immediate technical community. It is an explicit
   call to those outside of the related Working
   Groups or the W3C itself for implementation and
   technical feedback.
2. A Proposed Recommendation is work that (1)
   represents consensus within the group that
   produced it and (2) has been proposed by the
   Director to the Advisory Committee for review.
3. A Recommendation is work that represents
   consensus within W3C and has the Director's stamp
   of approval. W3C considers that the ideas or
   technology specified by a Recommendation are
   appropriate for widespread deployment and promote
   W3C's mission.

47
III THE BIG PICTURE REVISITED
48
W3Cs Semantic Web Principles

• Everything identifiable is in the Semantic Web
  (URIs!)
• Partial information
• Anyone can say anything about anything
• Web of trust
• All statements on the Web occur in some context
• Evolution
• Allow combining independent work done by
  different communities
• Minimalist design
• Make the simple things simple, and the complex
  things possible
• Standardize no more than is necessary

49
Hypertext Then and Now

• SOTA circa 1990 Dynatexts electronic book
• A book had to be compiled (like a program) in
  order to be displayed efficiently
• A central link database, to make sure there were
  no broken links
• Text that was fixed and consistent (a whole book)
• WWW
• Links can be added and used at any time
• Distributed (must live with broken links!)
• Decentralized

50
Knowledge Representation Now and Tomorrow

• To webize KR in general is, in many ways, the
  same as to webize hypertext. Replace identifiers
  with URIs. Remove any requirement for global
  consistency. Put any significant effort into
  getting critical mass. Sit back.
• -- TBL

51
Whats Going On Out There The Good, the
Bad/Not-So-Good, and the Wacky

• Web services (WSDL, DAML-S, )
• Query and Rule languages
• Web of trust

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Whats Going On Out There The Good, the
Bad/Not-So-Good, and the Wacky

• Web services
• Query and Rules
• Web of trust
• Will the masses create semantic annotations?

53
Whats Going On Out There The Good, the
Bad/Not-So-Good, and the Wacky

• Web services
• Query and Rules
• Web of trust
• Will the masses create semantic annotations?
• Birds of a feather
• The Me Llamo link type
• The Wiki Wiki Web

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Ongoing Work in Our Group

• EXPECT (k acquisition and problem solving)
• No longer developing KBs, but importing schemas
  and data
• Electric Elves
• Agents are more transparent and publish data
  schemas, advertisements/assumptions
• TRELLIS (try it out at trellis.semanticweb.org!)
• Users represent decisions and opinions -gt Web of
  Trust Gil Ratnakar, ISWC 02
• IKRAFT
• Users turn text in progressively more formal
  representations (KB) -gt semi-formal annotations

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TRELLIS Developing the Web of Trust One Citizen
at a Time

• Capture decisions and opinions as the user finds,
  analyzes, and uses information
• annotate the reasons, judgment, and purpose that
  make information meaningful
• keep track of contradictory, related, and
  rejected information
• annotate derivation of conclusions and
  formulation of hypotheses
• add structure and formalization incrementally
• semantic markup language
• Derive an assessment of
• info sources based on
• individual opinions
• Try it out at
• http//trellis.semanticweb.org

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Notation 3

• Test filter in N3
• Use
• cwm rules12.n3 -think -filterfilter12.n3
• should conclude that granpa is ancestor of
  bill
• _at_prefix log lthttp//www.w3.org/2000/10/swap/loggt
  .
• _at_prefix daml lthttp//www.daml.org/2001/03/damloi
  lgt .
• _at_prefix ltgt .
• _at_prefix rules ltgt .
• SimplifiedDanC challenge - simplied version of
  rules13.n3
• this logforAll ltpgt .
• ltpgt a damlTransitiveProperty . logimplies
• ltxgt ltpgt ltygt. ltygt ltpgt ltzgt.
  logimplies ltxgt ltpgt ltzgt. .
• this logforAll ltxgt , ltygt , ltzgt.

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