WSMX ­ INFRASTRUCTURE FOR EXECUTION OF SEMANTIC …

    WSMX ­ INFRASTRUCTURE FOR EXECUTION OF SEMANTIC
                     WEB SERVICES
                                Michal Zaremba, Armin Haller, Maciej Zaremba, Matthew Moran

                                       Digital Enterprise Research Institute, DERI, Ireland
                           {michal.zaremba, armin.haller, maciej.zaremba, matthew.moran}@deri.org


ABSTRACT
In this paper we present a demo implementation of an event driven system, which aims to enable execution of Semantic
Web Services. Our demo infrastructure is based on the Web Service Modeling Ontology (WSMO) [Roman et al., 2004].
The implementation follows research carried out by the Web Services Modeling Execution1 working group. WSMX is a
Service Oriented Architecture (SOA) and allows an agent acting on behalf of a user to talk to WSMX enabling discovery,
selection, mediation and invocation of formally described Web Services to carry out specific client tasks. Through the
implementation of WSMX we aim to prove the viability of WSMO and although the first implementation of the system
remains incomplete in terms of the required functionality, all components are in place and the system is capable of
executing simple scenarios. Through continuous open source development2 we aim to enhance WSMX with the intended
functionality for all defined conceptual components.

KEYWORDS
Semantic Web Services, Event Oriented Architecture, Service Oriented Architecture


1. INTRODUCTION
Web Services constitute one of the hot areas in web technology supporting the remote invocation of business
functionality over the Internet through exchange of well defined standardised messages. Existing Web Services'
technologies already provide the basic functionality for discovering (UDDI), interface description (WSDL) and
messaging (SOAP) in heterogonous, autonomous and distributed systems. Ongoing developments in the area of Web
Services constitute the future way of providing value-added services over the Internet. Despite the promises given by
inventors of Web Services standards and technologies about their automated or semi-automated execution, in reality Web
Services remain almost nothing more than enhanced RPC calls over Internet. Most of the Web Services used today
support one-way data retrieval and update functions (getting schedules, selling tickets, checking quotes etc.), which are
hard coded into software programs. While useful, they do not provide semi-automated or automated fulfilment of
customers' goals (Web Services can not be automatically bound to requestor goals at run time). Also the functionality
required by B2B & EAI systems is currently not supported by Web Services standards. The complex issues surrounding
system integration are well documented, but no Web Services software infrastructure currently exists that tackles this
problem. We are building our system on the most recent research in the area of Semantic Web Services. The intentional
purpose of Web Services Execution Environment (WSMX) is to support the functionality of B2B & EAI integration
systems while fulfilling the promise of automatic (semi-automatic) service discovery, selection, mediation and execution.


2. WSMO, WSMX AND WSML
The application of ontologies to Web Services is seen as a key requirement to enable semantics-driven data access
and processing [Bussler et al., 2002]. There are currently three initiatives providing semantic mark-up and the
means for semi-automated discovery, composition and execution of Web Services: OWL-S (formerly DAML-S)
[OWL Service Coalition, 2004], METEOR-S [Patil et al., 2004] and WSMO [Roman et al., 2004].

1
    WSMX ­ http://www.wsmx.org/
2
    Sourceforge ­ WSMX hosting site - http://sourceforge.net/projects/wsmx
WSMX is based on WSMO and its underlying formalized representational languages family WSML. WSMO itself is a
Semantic Web Services initiative being led by DERI3 and several EU projects (DIP 4, SEKT 5 and Knowledge Web 6) to
provide an ontology describing various aspects related to Semantic Web Services such as dynamic discovery, mediation,
choreography, orchestration and invocation. The conceptual foundation for WSMO has been defined in the Web Service
Modelling Framework (WSMF) [Fensel/Bussler, 2002].
WSMX is a reference implementation for WSMO defining its own conceptual model [Cimpian et al., 2004], execution
semantics [Oren, 2004], architecture [Zaremba et al., 2004] and implementation [Moran et al., 2004]. There are also use
cases provided by WSMX working group [Haller, 2004]. Once other aspects of execution of Semantic Web Services
such as for example choreography and orchestration are conceptually defined through the WSMO initiative, they will
become part of WSMX as well. Internally the execution semantics of WSMX provide the reliability, security and trust
required by industrial B2B & EAI integration systems. WSMX provides a mechanism to compile (checks syntax
correctness and converts to internal system data representation) semantic descriptions of Semantic Web Services that
have been described using Web Services Modelling Language (WSML)7. The formal definition of WSML language is
provided in [de Bruijn, 2004].


3. WSMX ARCHITECTURE




                                            Figure 1: WSMX Architecture




3
  Digital Enterprise Research Institute (DERI) - http://www.deri.org/
4
  DIP ­ http://dip.semanticweb.org/
5
  SEKT - http://sekt.semanticweb.org/
6
  Knowledge Web ­ http://knowledgeweb.semanticweb.org/
7
  WSML ­ http://www.wsmo.org/wsml
WSMX offers complete support for interacting with Semantic Web Services. These Web Services must provide a
WSMO-compliant (WSML) description of themselves specifying their capability, how to interact with them, the
ontologies they use along with other properties. Figure 1, above, presents the architecture that has been partially
implemented for the first version of WSMX and is going to be fully supported in subsequent implementations. The
WSMO Editor can be used at design time to create semantic description for Web Service, ontologies, mediators and
goals. WSMX provides a WSDL [WSDL, 2003] interface to accept these descriptions. Due to the WSDL interface the
creation of WSMO descriptions (capabilities) is not bound to a specific editor. There are already several initiatives to
design such an editor (within SWWS8 and DERI). Additionally to WSMO Editor, the Monitoring Tool also connects
through WSDL interface to watch functioning of the system. If requested by the Editor, any WSML file received through
the WSDL interface can be compiled and permanently stored in the system. The compiler component validates the
semantic descriptions and stores them persistently in the Ontology Repository.
          The WSMX Manager controls the operational flow of the system. It is also responsible for event management,
keeping a full record of the life cycle at each stage of processing user goal by the system. WSMX provides a Web
Service Interface described in WSDL [WSDL, 2003] to accept service requesters' goals. WSMX regularly scans for new
messages in a running state. Once a new message representing a requester goal is picked up, it is decomposed, validated
and translated into internal date representation by the Message Parser. The Matchmaker then attempts to match the client
goal to capabilities of Web Services, which are known to WSMX. The concept of Capability is used by WSMO to
formally describe the functionality a Web Service offers. Any Web Service with a capability that matches the goal is
returned by the Matchmaker. In this version of WSMX, the logical expressions representing the postconditions and
effects of the requester goal are compared with the expressions for the postconditions and effects of capabilities for Web
Services known to WSMX. The Selector component selects the Web Service that provides the best match for the goal.
The initial version of the Selector in WSMX selects the first available service. The Data Mediator component finds a
mediator in the Ontology repository that can mediate between the ontology used by the goal (source) and that used by the
selected Web Service (target). Mediation is carried out based on a set of mapping rules between the two ontologies that
are applied to the instance data contained in the goal. Once the data has been mediated, it may need to be translated from
a logical language format to an XML format before it is included in the SOAP message sent by the Invoker to the target
service. This translation is the job of the XML Converter. Once the data is in a format that can be used during Web
Service invocation, the Invoker makes the actual Web Service invocation on the selected Web Service using the mediated
and converted data.
          Event-based communication is managed by the Event Manager. Components never communicate directly
(one component never calls the other component) but they create and consume events (or change status of existing
events), which are broadcast to all components subscribed to listen for events in the system. Such an approach
enables decoupling communication from processing, which enables flexible communication patterns and
facilitating flexible run-time architecture.
WSMX can be used by enterprises that want to electronically exchange business documents across the Web (see figure
2).




                                          Figure 2: B2B Integration with WSMX

8
    SWWS - http://swws.semanticweb.org/
It is assumed that partners may not know each other before carrying out business transactions and for this reason contract
negotiation and contract agreement are going to be essential elements to be supported by future WSMX implementations.
Each business partner exposes a set of WSMO-described Web Services with the capabilities to handle conversations
using any possible known B2B protocols. The contract agreement defines the roles of enterprises in the conversation.
The infrastructure provided by WSMX takes care of any necessary mediation between Web Services, ontologies,
business goals and also mediates between Web Services and goals.


4. CONCLUSION
Web Services merely support the remote invocation of business functionality over the Internet. WSMX - the reference
implementation for Semantic Web Services goes much further, as the system aims to enable any information systems to
interact with any other information system and to preserve message, process and protocol semantics. WSMX is able to
discover Web Services matching with the agent's goal as long as the service description in any variant of WSML is
stored in any WSMX service registry within the entity. In the same process WSMX can execute them and hence reduce
the time for completing the full process by avoiding any user interaction.


ACKNOWLEDGEMENT
The work is funded by the European Commission under the projects DIP, Knowledge Web, Ontoweb, SEKT, and
SWWS; by Science Foundation Ireland under the DERI-Lion project; and by the Austrian government under the
CoOperate programme.


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