Transcript Semantic Web

The Semantic Web
Week 12
Term 1 Recap
Lee McCluskey, room 2/07
Email [email protected]
Department of Computing And
Mathematical Sciences
Module Website:
http://scom.hud.ac.uk/scomtlm/chs2533
SW - Fundamental Idea - 1
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When implementing a typical software application most of
the “semantics” of the data we use in bound up with the
procedures we write to manipulate that data.
So ‘data files’ only make sense to the methods we write to
manipulate them
Relational data bases are a bit better and open to multi-use
– but even here the programmer embeds what the relations
‘mean’ in the application code.
Current data on the internet is largely unstructured and not
amenable to processing. The data is by definition very rich
and inherently structured.
SW - Fundamental Idea - 2
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A requirement of the semantic web is to have all public
(www) ‘data’ encoded in a way that ANY application
program can use it – even programs that have no encoding
to anticipate the meaning of the data.
A second (dual) requirement of the semantic web is to have
all public (www) processes or services encoded in a way
that ANY application program can use then - even
programs that have no encoding to anticipate the meaning
of them.
The meaning of the data / processes will therefore have to
be encoded
.. To be program-independent (declarative)
 .. To be accessible to the client program
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So all programs using the SW will have to ‘understand’
HOW to extract the meaning of data / services ie
understand the data or services’s meta-languages. This
meta-language will have to be Universal.
SW - Fundamental Idea - 3
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‘SOLUTION’:
 Convention
for syntax of meta-data =>
tags/attributes via XML
 Convention for data language defn (what tagged
data in what order) => XML Schema / DTDs
 Convention for relating data items => URI, RDF
 Convention for standardising names (tags) =>
vocabularies, ontologies
 Convention for giving meaning to vocabularies =>
using (description) logics, OWL, DAML, KIF
Related Modules + Subject Area
ClientServer and
Dist Systems
OO
Modelling
UML
OO Classes
Advance
Databases
Conceptual
Schema and
Description
logics
Ontologies
Advanced
Information
Systems
Artificial
Intelligence
Shared
services
Logic and
reasoning
SEMANTIC
WEB
Semantic
notations
Language
Specification
And Implementation
recap
WEEK 1 lecture: Introduction to the Module
WEEK 2 lecture: Introduction to the Semantic Web
WEEK 3 lecture: XML / XML Schema
WEEK 4 lecture: RDF and RDFS
WEEK 5 lecture: RDFS / Introduction to Ontologies
WEEK 6 lecture: Capturing Conceptual Knowledge with Logic
WEEK 7 lecture: FOL
WEEK 8 lecture: Reasoning with FOL
WEEK 9 lecture: Reasoning with FOL
WEEK 10 lecture: Description logics: Introduction
WEEK 11 lecture: Description logics, OWL
WEEK 12 lecture: Recap
Recap – XML / XMLS
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XML is a convention for packaging up data with its metadata. Data is stored within tags and with a pointer to its data
language parser via DTDs.
Idea of URI – unique identifier for all ‘resources’.
Namespaces are a shorthand for giving and using URIs to
things. Without them all the terms we use in an internet
document would have to use the full URI !
XML schema documents are used to VALIDATE XML
documents.
XMLS is a more expressive, ambitious form of documenting
the syntax of your XML data than using DTDs. Further, an
XML Schema is an XML document itself.
Recap – RDF / RDFS
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Introduce a convention that we will (at the basic level)
describe data as ‘resource – property – value’ triples.
Fixed set of tags for this purpose
http://scom.hud.ac.uk/scomtlm/Artform/planning.html
RDFS – new tags such as
Class, property, label, subclass
Basic ontologies can therefore
Be written in RDFS
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Author
Lee McCluskey
Recap - Ontologies
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A formal, shared, specification of a
conceptualization, where a conceptualization is “an
abstract, simplified view of the world”
Encode more structured information than RDBs –
can use them to do simple reasoning with instances
and classes
Interpretation
C subset of X U Y
D&Y => Z
Ontology
X
Y
Conceptualisation
“an abstract, simplified view of the world”
Reality
Recap – FOL
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A way of specifying a conceptualisation using Wffs
Wff W is true in an interpretation I if W
evaluates to true under I.
w logically follows from W
if and only if every interpretation
that makes W true also makes w true
Recap – logic interpretations
Ax Ey R(y,x)
These 2
Interpretations
SATISFY this WFF
Greater_than
Mother_of
persons
WFF =
“Given any person there is
Someone who is their mother”
numbers
WFF =
“Given any number there
Is some number greater than it”
Recap – reasoning with FOL
Resolution Refutation: To PROVE Wff2 FROM Wff1
1. Translate Wff1 to CLAUSAL FORM
2. Translate ~ Wff2 to CLAUSAL FORM
3. Get contradiction from 1 + 2 using Resolution
…. If follows that Wff1 |- Wff2
But use of FOL controversial as:
- Reasoning not tractable in general
- FOL language ‘flat’ – not designed for the SW!
Recap – Description Logic
DL was designed for use in formalising diagrammtic notations used
in OO Modelling, Semantics Nets, Ontology description etc
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It is more compact than FOL
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It is built around the notion of concepts/classes - a concept or class
is the set of individuals x that satisfy some Wff(x)
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Its basic reasoning mechanism is subsumption – does one class
subsume another?
Eg E_Fatherof.Male (the set of fathers who have sons)
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Eg Person with > 2 degrees subsumes Person with > 3 degrees
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OWL-DL is a notation for a DL. Reasoning with OWL is based on
the “Open World Assumption”.
New Draft Schedule for next term
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Week 13 lecture: Building Ontologies with Protégé/Owl
Week 14 lecture: Building Ontologies with Protégé/Owl
Week 15 lecture: Intelligent internet agents – basics. types of agent multi agents, mobile agents, information agents
Week 16 lecture: Intelligent internet agents – reasoning+planning,
Week 17 lecture: Intelligent internet agents – adaptation+ learning
Week 18 lecture: Semantic web services: automated reasoning with
web pages;
Week 19 lecture: Semantic mark-up for web services: service
description languages eg DAML-S and OWL-S
Week 20 lecture: Automated service composition and service discovery;
Week 21 – 23: applications, domain modelling example?