1. From SHIQ and RDF to OWL: The Making of a Web Ontology Language
Ian Horrocks Peter F. Patel-Schneider and Frank van Harmelen
Presented by Zonghui Lian

2. Ontology Languages So far, how many ontology languages we can know
XOL (XML-based Ontology Exchange Language)
SHOE (Simple HTML Ontology Extension)
OML (Ontology Markup Language)
RDF(S) (Resource Description Framework (Schema))
OIL (Ontology Interchange Language)
DAML+OIL (DARPA Agent Markup Language + OIL)
OWL (Ontology Web Language)

3. XML – XML Schema
XML provides a standardized syntactical way to expose structural information
XML schema allows to define a schema for XML documents and may already provide machine-understandable semantics of data
Do not attach meaning to structural information

4. RDF Schema RDFS is too weak to describe resources in sufficient detail
No localised range and domain constraints
For example, can’t express such a subclass of person: the person who has children.
No existence/cardinality constraints
Can’t say that all instances of person have a mother that is also a person, or that persons have exactly 2 parents
No transitive, inverse or symmetrical properties
Can’t say that isPartOf is a transitive property, that hasPart is the inverse of isPartOf or that touches is symmetrical
Difficult to provide reasoning support
RDF has fact-stating ability.
Symmetric: if P(x, y) then P(y, x)
Transitive: if P(x,y) and P(y,z) then P(x, z)
Functional: if P(x,y) and P(x,z) then y=z
InverseOf: if P1(x,y) then P2(y,x)
InverseFunctional: if P(y,x) and P(z,x) then y=z
allValuesFrom: P(x,y) and y=allValuesFrom(C)
someValuesFrom: P(x,y) and y=someValuesFrom(C)
hasValue: P(x,y) and y=hasValue(v)
cardinality: cardinality(P) = N
minCardinality: minCardinality(P) = N
maxCardinality: maxCardinality(P) = N
equivalentProperty: P1 = P2
intersectionOf: C = intersectionOf(C1, C2, …)
unionOf: C = unionOf(C1, C2, …)
complementOf: C = complementOf(C1)
oneOf: C = one of(v1, v2, …)
equivalentClass: C1 = C2
disjointWith: C1 != C2
sameIndividualAs: I1 = I2
differentFrom: I1 != I2
AllDifferent: I1 != I2, I1 != I3, I2 != I3, …
Thing: I1, I2, …
Legend:
Properties are indicated by: P, P1, P2, etc
Specific classes are indicated by: x, y, z
Generic classes are indicated by: C, C1, C2
Values are indicated by: v, v1, v2
Instance documents are indicated by: I1, I2, I3, etc.
A number is indicated by: N
P(x,y) is read as: “property P relates x to y”

5. Requirements
Desirable features identified for a Web Ontology Language :
Compatible with existing Web standards (XML, RDF, RDFS)
Easy to understand and use
Formally specified
Has “adequate” expressive power
Tools for reasoning support

6. Layers of Languages Attribution Explanation We are here!
Identity
Standard Syntax
Metadata
Ontologies
Rules & Inference
Explanation
Attribution
Complexity could be a problem

7. OWL (Ontology Web Language)
OWL is now a W3C Recommendation
The purpose of OWL is identical to RDFS i.e. to provide an XML vocabulary to define classes, properties and their relationships.
RDFS enables us to express basic relationships and has limited inferencing capability.
OWL enables us to express much richer relationships, thus yielding a much enhanced inferencing capability.
The benefit of OWL is that it facilitates a much greater degree of inferencing than you get with RDF Schema.

8. Comparison RDF and OWL

9. Introduction of OWL (Ontology Web Language)
Description logic and frames
Many characteristics of RDF
The frame includes the name of the class, identifies the more general class (or classes) that it specialises, and lists a set of “slots”. A slot may consist of a property-value
pair, or a constraint on the values that can act as slot “fillers” (in this context, value means either an individual or a data value). This structure was used in the OIL language, with some enrichment of the syntax for specifying classes and slot constraints so as to enable the full power of a Description Logic style language to be captured.

10. D.L’s Influence on OWL Semantics are well defined.
OWL uses D.L model theory to formalise the meaning of the language.
Advantages
Reasoning technique --- check the consistency of classes and ontologies, and to check entailment relationships. Assume a query …

11. D.L’s Influence on OWL Language constructors Expressive power
Class (property) constructors
Axioms
Conflict with the computational complexity
OWL entailment
Blance
Boolean connectives, restriction on properties, transtive properties, and property hierarchy

12. D.L’s Influence on OWL Datatypes Difference with Advantage
Decrease the complexity & easy to answer question
“-5 nonNegative ?”
Totally seperated, 2nd indicates abstract concepts.

13. Origins of OWL DARPA Agent Markup Language DAML
Ontology Inference Layer
OIL
RDF
EU/NSF Joint Ad hoc Committee
DAML+OIL
All influenced by RDF
Oil: the precise details of RDF semantics.
OWL provides the complex inferences, undecidable.
OWL Lite
OWL DL
OWL Full
A W3C
Recommendation
OWL

14. Versions of OWL
Depending on the intended usage, OWL provides three increasingly expressive sublanguages
OWL Full
Full: Consider the compatibility with RDF and RDFS as the primary importance. no computation guarantees
DL (Description Logic): Friendly syntax, decidable inference. computationally complete
Lite: Simpler syntax and more tractable inference.
OWL DL
OWL Lite

15. Advantages/Disadvantages of versions
Full:
The advantage of the Full version of OWL is that we get the full power of the OWL language.
The disadvantage is that it is very difficult to build a computational tool for this version and may not get a quick and complete answer.
DL/Lite:
The advantage of the DL or Lite version of OWL is that tools can be built more quickly and easily, and users can expect responses from such tools to come quicker and be more complete.
The disadvantage is that we don't have access to the full power of the language.

16. OWL as D.L

17. OWL as D.L

18. Conclusion Difference b/w OWL DL & D.L:
Datatyping mechanisms (XML schema datatypes)
RDF URI reference as name
Entailments OWL DL is compatible with that of RDF and RDFS