and Semantic Web Services

religiondressInternet και Εφαρμογές Web

21 Οκτ 2013 (πριν από 3 χρόνια και 1 μήνα)

104 εμφανίσεις

1

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

Languages for the Semantic Web
and Semantic Web Services

Current Efforts and Challenges for ASP


Axel Polleres

axel.polleres@deri.org


2

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

Semantic Web


Publish machine
-
processable meta
-
data on the Web (semantic Web idea!)!


Provide the means to publish data on relations of resources and taxonomies of data on the Web


Provide standards on top of XML to describe the meaning of published knowledge


This meta
-
data shall ideally be
consensual (Ontologies!).












3

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

Overview


OWL


Semantic Web


RDF(S), OWL, SWRL, SWRL FOL


Semantic Web Services


SWSL
-
Rules


WSML


Challenges

4

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

OWL


卥浡湴楣S坥W

RDF(S), OWL, SWRL, SWRL FOL


RDF(S)
W3C Recommendation, latest version,10 February 2004


simple taxonomies, express structured knowledge in a
graph made up of
<subject predicate object>

triples


OWL
W3C Recommendation, latest version,10 February 2004


SWRL
W3C member submission, 21 May 2004


extends OWL DL by simple rules, quite restrictive, but
undecidable already.



This is not all!


Several drawbacks, several alternative suggestions. Let's see the results of the
current Rules Workshop going on this minute in Washington.

5

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

RDFS
-

OWL Lite/DL/Full

inappropriate Layering


OWL DL is not properly
layered on top of RDFS
syntactically…



… even worse: Given the
same (OWL DL) ontology
there are things
semantically entailed by
OWL Full, not entailed by
OWL Lite…


… something's strange here!



6

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

OWL DL is not properly layered on top
of RDFS syntactically:


OWL does not smoothly integrate:


No meta
-
statements in OWL Lite and DL (i.e.
separate vocabulary:



RDF Triples:




hansi rdf:type eagle.




eagle rdf:type species.



Not possible in OWL Lite and DL!

7

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

Given the same (OWL DL) ontology there
are things semantically entailed by OWL
Full, not entailed by OWL DL…


From OWL Semantics and abstract Syntax document:







The "only if" direction is not true!



I.e., OWL Full adds additional inferences on the
same
OWL DL ontology!






Theorem 2:

Let O and O' be collections of OWL DL ontologies and axioms and facts in

abstract syntax form that are imports closed, such that their union has a
separated vocabulary
.

Given a datatype map D that maps xsd:string and xsd:integer to the appropriate XML Schema

datatypes and that includes the RDF mapping for rdf:XMLLiteral, then the translation of O

OWL Full entails

the translation of O' with respect to D if the translation of O
OWL DL entails


the translation of O' with respect to D.

8

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

OWL DL entails less than OWL full:

Axel friendOf Lea .

²
OWL Full



Axel rdf:type
:
x .

:

x owl:onProperty friend .

:

x owl:minCardinality "1"xsd:nonNegativeInteger .


But:



Axel friendOf Lea .


²
OWL DL


Axel rdf:type :x .


x owl:onProperty friend .


x owl:minCardinality "1"xsd:nonNegativeInteger .


Woulld need additionally:


Axel rdf:type owl:Thing.


Lea rdf:type owl:Thing .


friend rdf:type owl:ObjectProperty .

9

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

SWRL


OWL unsatisfactory expressivity, not even simply rules like:



parent(?x,?y)


brother(?y,?z)


uncle(?x,?z)





SWRL extends OWL with a simple rule language which allows
concept (unary) and role (binary) predicates as well as sameAs
(equality) and differentFrom (inequality) as atoms.



Undecidable, if not further restricted (e.g. to Description logic
programs)



SWRL FOL W3C member submission April 11th:


Proposal to loosen some of the restrictions of SWRL to handle
function
-
free handle unary/binary first
-
order logic, n
-
ary
predicates only via reification.

10

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

RDF(S), OWL, SWRL syntax


All of these standards offer XML exchange
syntaxes



RDF exchange syntaxes:


OWL/RDF, SWRL/RDF exchange syntax are not really useful: puts
OWL constructs inside an RDF graph themselves, causes problems
with OWL DL and OWL Full semantic interoperability

11

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

Semantic Web Services

-

Requirements


Semantic descriptions of the functional and behavioral aspects of Web Services to
enable (semi
-
)automatic discovery, composition and execution of Web Services,
build upon Web Services technologies (SOAP, WSDL, UDDI).


pre
-
postconditions


Interfaces


Mediators


Capability


User goals, preferences



Currently three major initiatives:


OWL
-
S … an OWL ontology to semantically describe Web Services (OWL)


WSMO/WSML/WSMX … a general framework for SWS description (own logical
language)


SWSL … a framework for SWS description based on OWL (but also own language)



Another W3C workshop in June in Innsbruck:

Frameworks for Semantic Web Services … deadline for position papers extended to Friday
April 29th!

12

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

Why OWL is not enough for SWS?


Permit FOL for ontologies beyond DL/OWL: Need to express
complex conditions, rules, trust policies for contracting,
nonmon. features, prioritization, dynamics



Integrate nonmon., frame/OO, DDB ontologies with mon.
DL/FOL ontologies



Cope robustly with conflict between ontologies, e.g., merging
OWL ontologies from many sources



OWL
-
S does not define the semantics of dynamics, proposes to
allow DRS,KIF,SWRL for expressing pre
-
conditions, effects,
etc. but does not specify the semantics.


13

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

SWSL
-
Rules


Semantic Web Service Language initiative


(Micheal Kifer, David Martin, Benjamin Grosof, … DAML
founded plus European participants)



Ontology/Rules Language:


SWSL Rules


LP with NAF; Courteous, Hilog extensions


SWSL FOL


Shared presentation syntax; builds on F
-
Logic


Markup syntax


TBD probably with RuleML committee



W3C member submission planned



14

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

SWSL Language Layers:


Strong Consensus: Need
Nonmonotonic

LP.
And

FOL.


“SWSL
-
Rules” = the LP KR.


“SWSL
-
FOL” = the FOL KR.


Expressive Features for SWSL are similar to those
desired for SW rules in general, but with bit different
near
-
term importance/urgency:


Important in both:
Prioritization, NAF

(cf. Courteous LP)


Important in both, more urgent in SWS than SW overall:
Meta
-

power/convenience:
Hilog, frame syntax

(cf. F
-
Logic)


A bit more important in SWS than SW overall:
Lloyd
-
Topor
(nested expressions)


Reification: meta
-
knowledge/modeling, mentioned already
in RDF, but no semantics for it.

15

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

SWSL Rules + SWSL FOL


Semantics for rules part and FOL part separate


Exchange syntax RuleML


New fundamental KR theory is needed to unify nonmon. LP with FOL


"A holy grail for SWS, and for SW generally"


16

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

WSML

(joint work with Jos de Bruijn, Holger Lausen, Dieter Fensel, Michael Kifer)



Developed as joint effort in several EU Projects (dip, SEKT,
KnowledgeWeb)



Based on Web Service Modeling Ontology WSMO



Also has its own rules language, similarities with SWSL



W3C member Submission pending


17

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

Web Service Modeling Language


Four elements of WSMO:


Ontologies


Goals


Web Services


Mediators


WSML provides a formal grounding for the
conceptual elements of WSMO, based on:


Description Logics


Deductive Databases


First
-
Order Logic

18

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

Syntaxes for WSML


Human
-
readable syntax


Layered syntax


Inspired by OIL/OWL and F
-
Logic


Two flavors:


Conceptual syntax


Logical Expression Syntax


Semantics is fixed in WSML variants


XML syntax


RDF syntax


Mapping to OWL

19

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

Variants of WSML logical
languages

20

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

Variants of WSML (contd.)


WSML
-
Core


Based on the intersection of Description Logics and Datalog


Has (frame
-
based) conceptual syntax and logical expression
syntax


WSML
-
Flight


Layered on top of WSML
-
Core


Basic meta
-
class facility


Constraints


Non
-
monotonic features (default negation)


Provides more intuitive modeling constructs (for people with
DB/SE background)


Preferred ontology modeling language


Based on Datalog with stratified negation and inequality

21

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

Variants of WSML (contd.)


WSML
-
Rule


Based on Logic Programming with default negation and F
-
Logic/HiLog syntactical extensions


Preferred goal/web service modeling language


WSML
-
DL


Based on SHIQ


WSML
-
Full


Combining FOL with minimal models and non
-
monotonicity



22

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

WSML Logical Expressions


Elements:


Function symbols (e.g.
f()
)


Variables (e.g.
?x
)


The syntax is based on F
-
Logic style molecules, e.g.




Human
subClassOf

Animal
.




Axel
memberOf

Human
,





Axel[name
hasValue

“Axel Polleres”]
.


Predicates (e.g.
distance(?x, ?y,?z)
)


Logical connectives (
or
,
and
,
not
,
impliedBy
,

equivalent
,

implies
,

forall
,

exists, :
-
, !
-
),


ASCII, but readable, more or less directly translatable to
XML tags.


Example:


?x
memberOf

Human
equivalent

?x
memberOf

Animal
and

?x
memberOf

LegalAgent.




23

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

WSML
-
Core


Allows conceptual modeling of ontologies


Based on Description Logic Programs subset of OWL


i.e., efficient query answering


Should be easily adopted in existing implementations (e.g. XSB,
OntoBroker, SWI
-
Prolog, KAON, DLV)


Import/export OWL ontologies


Datatype support based on XML Schema datatypes and OWL
-
E


Expressive enough for most current ontologies


Properly layered on top of RDF/RDFs worked upon, currently
restrictions on the use of RDF(S) vocabulary.


Can be used for limited goal/web service modeling

24

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

WSML
-
Flight


Is an extension of WSML
-
Core


Adds limited support for nominals


Stays in LP world


Meta
-
modeling


Adds inequality (plus UNA!)


Adds constraints (wrt. local knowledge base)


Adds stratified non
-
monotonic negation


Allows arbitrary safe Datalog rules (i.e. no function
symbols; rules must be safe)


Language is based on Datalog with inequality,
constraints and stratified negation


25

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

WSML
-
Rule


Extension of WSML
-
Flight



Allows unrestricted use of function symbols


Non
-
stratified negation (current suggestion:
use wfs)


Possibly other features


26

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

WSML
-
DL


Equivalent to SHIQ with datatype extension




Open questions:


DL epistemology?


DL concrete syntax for logic expressions?

27

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

WSML
-
Full


Based on a combination of First
-
Order Logic and
minimal model semantics and default negation


Unifies rule language with first
-
order based language



Possible formalisms:


Autoepistemic Logic


Default Logic


Circumscription

28

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

WSML Goals and Web
Services


Goal / Web Service assumptions/effects and
pre/post
-
conditions are defined through WSML
logical expressions


Logical expressions rely on ontologies



Use of ontologies through


Ontology import


Mediation



Open issue: semantics of dynamics, interfaces,
grounding

29

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

WSML Conclusions


WSML is concrete language for modeling:


Ontologies


Web Services


Goals


Mediators


Variants:


WSML
-
Core


WSML
-
Flight


WSML
-
Rule


WSML
-
DL


WSML
-
Full


Modular, Frame
-
based


Conceptual syntax vs. Logical Expressions


Syntaxes:


Human readable


XML


RDF


Mapping to OWL



More cautious, less variants than SWSL (which also doesn't explicitly tackle interoperability
with OWL).




30

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

Summary


The current W3C recommendations have some unresolved issues



The discussion in the semantic Web community are often more about syntax than about
semantics



More expressivity than OWL is necessary, the standards discussion is not over!



Challenges:

For the "ontological reasoning" part:


Fix semantic layering mess on top of RDF/RDFS


Semantic Interoperability of Knowledge bases building on different paradigms.


Engines: Support/frontends for XSD/XPath built
-
ins, Frame
-
based syntax. Efficient, modular
reasoning support.


Implies: Accept incomplete reasoning in some cases.


How to unify the DL, FOL and LP worlds? What is the semantics of a unifying umbrella language!?!


Reasoning with networks of ontologies, rewriting, etc.

For the Web Services Part:


Formalizing dynamic aspects of Semantic Web Services (pre
-
/postc., interfaces) in a way
interoperable with ontologies:


Idea: use of action theories, action languages, mappings from/to process languages, etc.

Thank you!

<questions?/>

31

Dagstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints "

Additional slide:


Desirable features of a unified logical framework:


arbitrary use of neg/naf?


Combination of wfs/sm knowledge bases?


Nested expressions + quantifiers


Define easily checkable layered syntactical restrictions with
increasing expressive power and computational properties
(also WITHIN LP, tight, etc.) in order to support modular
reasoner
-
support.