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A NOVEL APPROACH TO WEB SERVICES DISCOVERY. Università di Milano-Bicocca. Marco Comerio. [email protected] Index. Objectives & Motivations The Web Services Modeling Ontology (WSMO) Non-functional Properties (NFPs) The NFP-based Discovery Process Conclusions and Future Works.

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a novel approach to web services discovery

A NOVEL APPROACH TO WEB SERVICES DISCOVERY

Università di Milano-Bicocca

Marco Comerio

[email protected]

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

index
Index
  • Objectives & Motivations
  • The Web Services Modeling Ontology (WSMO)
  • Non-functional Properties (NFPs)
  • The NFP-based Discovery Process
  • Conclusions and Future Works

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

objectives
Objectives
  • 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.

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

motivations
Motivations
  • 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).

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

motivations1
Motivations
  • 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.

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

index1
Index
  • Objectives & Motivations
  • The Web Services Modeling Ontology (WSMO)
  • Non-functional Properties (NFPs)
  • The NFP-based Discovery Process
  • Conclusions and Future Works

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

the web services modeling ontology wsmo
The Web Services Modeling 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

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

the web services modeling ontology wsmo1
The Web Services Modeling 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.

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

index2
Index
  • Objectives & Motivations
  • The Web Services Modeling Ontology (WSMO)
  • Non-functional Properties (NFPs)
  • The NFP-based Discovery Process
  • Conclusions and Future Works

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

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.

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

non functional properties nfps1
Non-functional Properties (NFPs)
  • 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.

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

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.

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

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.

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

non functional properties nfps2

Web Service Description

Goal

NFP-Policy

offNFPs

NFP-Request

conNFPs

Non-functional Properties (NFPs)

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

index3
Index
  • Objectives & Motivations
  • The Web Services Modeling Ontology (WSMO)
  • Non-functional Properties (NFPs)
  • The NFP-based Discovery Process
  • Conclusions and Future Works

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

the nfp based discovery process
The 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

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

mediation
Mediation
  • 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.

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

matching rules
Matching 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)

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

quantitative matching rules examples
Quantitative Matching Rules: Examples
  • 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

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

functional discovery
Functional 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.

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

nfp evaluation
NFP 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.

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

nfp evaluation1
NFP 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:

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

filtering
Filtering
  • 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:

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

ranking
Ranking
  • 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.

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

index4
Index
  • Objectives & Motivations
  • The Web Services Modeling Ontology (WSMO)
  • Non-functional Properties (NFPs)
  • The NFP-based Discovery Process
  • Conclusions and Future Works

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

conclusions
Conclusions
  • 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.

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

future works
Future 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

thank you questions

Thank you!Questions?

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

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