A NOVEL APPROACH TO WEB SERVICES DISCOVERY

YR-SOC'07 - Leicester 11-12 June 2007

1

SEQUOIAS

A NOVEL APPROACH TO WEB SERVICES DISCOVERY

Marco Comerio

Università di Milano-Bicocca

[email protected]

YR-SOC'07 - Leicester 11-12 June 2007 2

SEQUOIAS

IndexIndex

Objectives & Motivations

The Web Services Modeling Ontology (WSMO)

Non-functional Properties (NFPs)

The NFP-based Discovery Process

Conclusions and Future Works


SEQUOIAS

ObjectivesObjectives

Definition of a technique to enrich SWS requests and descriptions with the specification of non-functional properties (NFPs);

Proposal of a novel approach to a NFP-based SWSs discovery;

Test and validation of the proposal in the WSMO environment.


SEQUOIAS

MotivationsMotivations

The discovery of a Semantic Web service (SWS) is the act of locating a machine-processable description of a SWS-related resource that may have been previously unknown and that meets certain functional criteria.

The increasing availability of SWSs that offer similar functionalities requires the discovery process to be enhanced with a selection phase that considers non-functional properties (NFPs) of the SWSs.

NFPs could be quite relevant to match a service request and a service description. In fact, even if a service matches the requested functionalities, it could be unacceptable in terms of NFPs (e.g., cost is too expensive).


SEQUOIAS

MotivationsMotivations

This scenario highlights two needs:

• enrichment of SWS descriptions with a well-defined set of NFPs;

• enhancement of the matching functionality between SWS requests and descriptions.


SEQUOIAS

IndexIndex







SEQUOIAS

The Web Services Modeling The Web Services Modeling Ontology (WSMO)Ontology (WSMO)

WSMO is an ontology for describing various aspects related to Semantic Web Services.

WSMO consists of four different main elements:

www.wsmo.org


SEQUOIAS

The Web Services Modeling The Web Services Modeling Ontology (WSMO)Ontology (WSMO)

Ontologies : provide the terminology;

Goals : define the problems to be solved;

Web Services : define various aspects of Web Services (e.g., Capabilities, Interfaces);

Mediators : allow the overcoming of data, protocol and process heterogeneity. They represent the main advantage of using WSMO and are of four different types: (i) wgMediator; (ii) ggMediator; (iii) ooMediator and (iv) wwMediator.


SEQUOIAS

IndexIndex







SEQUOIAS

Non-functional Properties (NFPs)Non-functional Properties (NFPs)

NFPs can be considered to be constraints beyond the functionalities of a Semantic Web Service.

The management of NFPs is not a simple task because:

• NFPs are characterized by several properties;

• NFPs are of different nature;

• NFPs are often inter-dependent.

Solution: address this problem by developing ontologies of NFPs (OntoNFPs) to formalize definitions, relations, dependencies, heterogeneous measurements and evaluation methods.


SEQUOIAS


Two different types of NFPs must be considered:• offered NFPs (offNFPs) to be included in SWS description;

• requested NFPs, that are, NFP constraints (conNFPs) to be included in SWS requests.

ConNFPs and OffNFPs can be classified as:• Qualitative: expressed by enumerative values;

• Quantitative: expressed by numeric values.

The strength of a good offered/required NFP description consists in supporting matching between requested and offered NFPs in a simple and effective way.


SEQUOIAS

Offered NFPs (offNFPs)Offered NFPs (offNFPs)

OffNFPs are NFPs supported by the provider of the SWS.

The concept of NFP-policy is introduced to collect a set of OffNFPs with a SWS.

More NFP-Policies can be associated with a SWS. Each Policy has an applicability condition defined through an axiom.


SEQUOIAS

NFP Constraints (conNFPs)NFP Constraints (conNFPs)

ConNFPs are requirements that the requester of a SWS wants to fulfill.

The concept of NFP-Request is introduced to collect a set of conNFPs with a Goal.

NFP-Request is introduced as a requester-side counterpart of NFP-Policy.


SEQUOIAS


Web Service DescriptionWeb Service Description

NFP-PolicyNFP-Policy

offNFPsoffNFPs

GoalGoal

NFP-RequestNFP-Request

conNFPsconNFPs


SEQUOIAS

IndexIndex







SEQUOIAS

The NFP-based Discovery ProcessThe NFP-based Discovery Process

A novel approach to WS discovery that enriches the traditional UDDI-based process with the use of semantics and evaluation of NFPs.

The proposed SWSs discovery process is composed of five different phases.

set up time execution time


SEQUOIAS

MediationMediation

Mediation is performed at setup time and aims at defining: • mediators : matching rules for pairs of conNFPs and

offNFPs stating when a conNFP is satisfied by an offNFP;

• meta-mediators : mediators identifying which matching rules need to be invoked for a NFP-Request.

Mediators and Meta-mediators are logic programs written in F-logic that are processed by a deductive engine.

The result of matching is not a boolean value, it is a positive numeric value that states the degree of satisfaction of a certain constraint.


SEQUOIAS

Matching RulesMatching Rules

Matching rules for qualitative and quantitative NFPs have been defined.

Quantitative matching rules for the most typical constraint operators have been defined.

The matching degree of pairs of quantitative <conNFP, offNFP> depends on the constraint operator op expressed in the NFP constraint and is computed by formulas like

Degree=fop(OffValue,ReqValue)


SEQUOIAS

Quantitative Matching Rules: Quantitative Matching Rules: ExamplesExamples

Constraint operator (≥ ) : values greater or equal than a reqValue. ReqValue is a lower bound and that the higher value is better.

Constraint operator (≥ ) : values at least equal than a reqValue. ReqValue is a lower bound and the lower value is better.

• if offValue>reqValue

• if offValue<reqValue

• if offValue=reqValue

reqValue

offValueDegree

reqValue

offValueDegree

reqValueoffValue

offValueDegree

NumberDegree max


SEQUOIAS

Functional DiscoveryFunctional Discovery

Functional Discovery is the traditional SWSs discovery process.

This phase has the goal of finding a list of SWSs that totally satisfy the functionalities required by an end-user.

This phase finds a set of candidate services; each one providing the same functionality but associated with different sets of policies.


SEQUOIAS

NFP EvaluationNFP Evaluation

NFP Evaluation is in charge of exploiting the matching rules stored in mediators and meta-mediators to compute the matching degree between a conNFP and an offNFP.

The result of the NFP Evaluation is a set of values in the range [0..n] associated with each NFP-policy of each SWS identified in the Functional SWS Discovery phase.


SEQUOIAS

NFP EvaluationNFP Evaluation

On these results, two indicators are defined:• normalized degree (n-degree): shows if offValue

matches a reqValue and is expressed by values in range [0..1] (if the result is >1 it is reduced to 1).

• extra matching degree (extraMatch): it is an additional information about how a conNFP is satisfied. It is expressed by values in range [0..1], and is computed by the formula:

)max(Degree

DegreeextraMatch i

i


SEQUOIAS

Filtering consists in discarding SWSs with NFP-Policies that do not satisfy user minimum requirements and in computing two numeric matching indicator for each NFP-Policy. It is

composed of three steps: • Mandatory NFPs-driven SWSs discarding : checks if the degree of

matching is equal to 1 for all conNFPs with relevance equal to 1. Otherwise, the related NFP-Policy is discharged.

• Calculus of NFP Global Normalized Value (NGNV) : for each NFP-Policy evaluates the NGNV with the following formula:

• Calculus of NFP Global ExtraMatch Value (NGEV) : for each NFP-Policy evaluates the NGEV with the following formula:

FilteringFiltering

n

iii rDegreeNGNV

1

*

n

iii rextraMatchNGEV

1

*


SEQUOIAS

RankingRanking

Ranking is in charge of sorting the policies of the SWSs on the basis of their NGNV values.

In the case of policies with the same NGNV value, their NGEV values are considered.


SEQUOIAS

IndexIndex







SEQUOIAS

ConclusionsConclusions

This ongoing work proposes:

• an ontological model to capture the nature and relations among NFPs;

• an enhancement of the discovery process with a selection phase that considers NFPs;

• two indicators, NGNV and NGEV, to measure the matching degree between requested and offered NFPs, in order to be able to filter, rank and select a set of services offering the same functionality;

• a set of matching rules to address the different kinds of constraints expressed by the requesters.


SEQUOIAS

FutureFuture Works Works

Experimental validation of the proposed approach in the WSMO environment;

Enhance the NFP ontological model to capture the dependency relations among NFPs;

Semi-automatic generation of mediators;

Management of NFPs in SWS composition.

These works are supported by the Single European Employment Market Place (SEEMP) project and the Networked Peers for Business (NeP4B) project.

YR-SOC'07 - Leicester 11-12 June 2007

28

SEQUOIAS

Thank you!Thank you!Questions?Questions?

Documents

A NOVEL APPROACH TO WEB SERVICES DISCOVERY