A Position statement on IRS-III: A Comprehensive Approach to Creating and Using Semantic Web Services
John Domingue, Liliana Cabral, Stefania Galizia, and Enrico Motta
Knowledge Media Institute, The Open University,
Milton Keynes, MK7 6AA, UK
{j.b.domingue, l.s.cabral, s.galizia, e.motta}@open.ac.uk
http://kmi.open.ac.uk/
Creating software applications requires time and effort from skilled IT specialists. Even when long standing software engineering practices are followed more often than not there will exist a gulf of execution [Norman, 1988] between the intentions and desires of users and the functionalities afforded by the developed software system. Over the past eight years we have been investigating how to alleviate the above problem through the use of intelligent brokers [Benjamins et al., 1998]. Our overall vision is that through the use of knowledge level descriptions our brokers will be able to automatically configure applications on-the-fly from components available over the internet to support a given user’s task.
Our early work led to the creation of the UPML framework [Fensel et al., 1999] which prescribed an epistemology for a library of reusable knowledge level components founded on tasks, problem solving methods and domain models. We then created the first version of the IRS [Crubezy et al., 2002]. The overall design goals for the IRS were two fold. Firstly, during the development phase the IRS enabled components to be combined easily through the use of a) a clear process model; b) semi-automated support for creating bridges between components; and c) an easy-to-use interface. Secondly, during execution the IRS acts as a broker between users/clients who have goals that are to be achieved and executable components available over the internet which provide functionalities.
The overall design of the most recent version of the IRS, IRS-III was driven by the fact that we wished to be compatible with emerging web service standards. At the ontological level we elected not to try and adapt the UPML framework but instead adopt and extend WSMO [Roman et al., 2005]. We had two main reasons for adopting WSMO. Firstly, WSMO is based on WSMF [Fensel and Bussler, 2002] which is itself partly descendent from UPML, thus, there was an existing strong relationship between the two frameworks. Secondly, the underlying epistemology of WSMO is based on web services, whereas UPML is based on an idealised conceptualisation of reusable knowledge intensive systems. At the implementation level IRS-III utilises web service protocols such as SOAP and is interoperable with standard web service technologies.
In this paper we focus on the design principles underlying IRS-III, gleaned from our deployment experiences, the IRS-III ontology and architecture. More details on IRS-III can be found in [Domingue, et. al, 2004] and [Galizia and Domingue, 2004].
Since 2002 we have been involved in a process of deploying the system for use with partners in collaborative projects such as the EU funded DIP project (see dip.semanticweb.org), the UK funded Advanced Knowledge Technologies (AKT) project (see www.aktors.org) and the MIAKT EScience project (see www.aktors.org/miakt/). Additionally, since 2003 we have used the IRS within an educational setting as part of the OntoWeb and KnowledgeWeb summer schools (see babage.dia.fi.upm.es/sssw05/) and as part of a hands on session within tutorials presented at the AIMSA and NetObjectDays and ISWC tutorials. In total IRS has been used to educate 150 students and conference attendees into the area of semantic web services.
The initial vision of an intelligent broker and the feedback we have received from our users have enabled us to generate a generic set of design principles for systems which aim to support the creation and use of semantic web services. We outline these below.
The starting point for our design is that web services are invoked by clients. A client may be a human end user invoking a web service for personal use, an employee of an organisation or a software program. In each case the client will exist in its own context which should be modelled within the semantic descriptions. This context will be quite different from that of the web service. For example, a personal end user may request a holiday with a preference for a certain climate, a location near particular cultural artefacts and amenable to children of a specific age range. The required flights and hotel booking web services will be described using concepts such as city and available date. Our view is that distinct ontological structures are required to describe potential users and web services. Moreover, within the IRS the independence between user desires and ontology means that we can specify user desire which may not in principle be satisfiable, even in principle, by a web service – for example “I want to be the UK Prime Minister”. Ontological role separation is also a principle which underlies WSMO [Feier, 2004].
Building on the principle above we enable clients (human users or application programs) to invoke a web service simply by specifying a concrete desired capability. The IRS acts as a broker finding, composing and invoking appropriate web services in order to fulfil the request. Implementing this principle relies on the fact that the semantic descriptions with the IRS are operational.
We have designed the IRS interfaces so that much of the complexity surrounding the creation of SWS based applications is hidden. For example, the IRS-III browser hides some of the complexity of underling ontology by bundling up related class definitions into a single tabbed dialog window.
A corollary of the above design principle. We have many users who have an existing system which they would like to be made available but have no knowledge of the tools and processes involved in turning a stand alone program into a web service. We therefore created the IRS so that it supports ‘one click’ publishing of stand alone code written a standard programming language (currently we support Java and Lisp) and of applications available through a standard web browser.
This principle is in part a consequent of the one-click-publishing principle. Within the design of the IRS we make no strong assumptions about the underlying service implementation platform. We do however accept the current dominance of the web services stack of standards and consequently program components which are published through the IRS also appear as standard web services with a SOAP based end-point.
When manipulating web services, whether manually or automatically, one needs to be able to reason about their status. Often this information needs to be computed on-the-fly in a fashion which integrates the results smoothly with the internal reasoning. To support this we allow functions and relations to be defined which make extra-logical calls to external systems – for example, invoking a web service. Although, this design principle has a negative effect on the ability to make statements about the formal correctness of resulting semantic descriptions, it is necessary because our domain of discourse includes the status of web services. For example, a user may request to exchange currencies using “today’s best rate”. If our representation environment allows us to encode a current-currency-rate relation which makes an external call to an appropriate web service then this will not only make life easier for the SWS developer but the resulting descriptions will be more readable.
Our aim is to make IRS-III as open as possible. The IRS-III clients are based on Java APIs which are publicly accessible. More significantly, components of the IRS-III server are semantic web services represented within the IRS-III framework. This feature allows our users to replace the main parts of the IRS broker with their own web services to suit their own particular needs.
Our view is that any data which can be represented is. This principle also holds for other SWS frameworks. For example, OWL-S [OWL-S, 2002] has a grounding and non functional properties. Nevertheless, we believe that this dimension is important enough to stress. It is not possible a priori to know which specific data will be required for SWS related reasoning.
In many parts of the life cycle of any software system it is important that the developers are able to understand the design and behaviour of the software being constructed. This is also true for SWS applications. This principle is concerned with making the semantic descriptions accessible in a human readable form. The descriptions could be within a plain text editor or within a purpose built browsing or editing environment. The key is that the content and form are easily understandable by SWS application builders.
One of the main aims for web services is to enable the interoperability of programs over the internet. A reasonable extension of this is that as far as possible SWS frameworks and platforms also should be interoperable. For this reason IRS-III has an OWL-S import mechanism [Hakimpour et al., 2004] and is interoperable with the WSMO reference implementation WSMX (see www.wsmx.org).
The IRS-III ontology is currently based on WSMO standard v 1.0 [Roman et al., 2004] with a number differences mainly derived from the fact that in IRS-III we aim to support capability driven web service invocation. To achieve this we require that goals and web services have input and output roles. In addition to the semantic type we also store the soap binding for input and output roles. Consequently a goal in IRS-III has the following extra slots: has-input-role, has-output-role, has-input-role-soap-binding and has-output-role-soap-binding. Note that in WSMO v 1.1 goal definitions now refer to a requested capability (of a potential web service) where the variables used with pre and post conditions, assumptions and affects are explicitly declared.
Goals are linked to web services via mediators. More specifically, the wg-mediators (wg-mediators in WSMO link goals and web services) found in the used-mediator slot of a web service’s capability. If a mediator associated with a capability has a goal as a source, then the associated web service is considered to be linked to the goal.
Web services which are linked to goals ‘inherit’ the goal’s input and output roles. This means that input role definitions within a web service are used to either add extra input roles or to change an input role type.
When a goal is invoked the IRS broker creates a set of possible contender web services using the wg-mediators. A specific web service is then selected using an applicability function within the assumption slot of the web service’s associated capability. As mentioned earlier the wg-mediators are used to transform between the goal and web service input and output types during invocation.
In WSMO the mediation service slot of a mediator may point to a goal that declaratively describes the mapping. Goals in a mediation service context play a slightly different role in IRS-III. Rather than describing a mapping goals are considered to have associated web services and are therefore simply invoked.
The IRS-III architecture is composed by the main following components: the IRS-III Server, the IRS-III Publisher, IRS-III Editors and the IRS-III Client, which communicate through a SOAP-based protocol, as shown in figure 1.
Fig. 1. The IRS-III Server Architecture
The IRS-III Server is based on an HTTP server written in lisp [Riva and Ramoni, 1996] which has been extended with a SOAP [SOAP, 2003] handler. Separate modules handle soap based requests from the browser, the publishing platforms and the invocation client. Messages result in a combination of queries to or changes within the entities stored within the WSMO library.
The IRS-III Browser and Editors provide simple interfaces enabling the creation and editing of WSMO based descriptions. The Browser provides multiple visualizations of the semantic descriptions which can be navigated by direct manipulation. The Editor combines related WSMO components into single multiple tabbed windows. For example, a web service window will contain the associated interface, capability, choreography and orchestration definitions.
Publishing with IRS-III entails associating a deployed web service with a WSMO web service description. When a web service is published in IRS-III all of the information necessary to call the service, the host, port and path are stored within a publisher-information class associated with the web service’s interface. Additionally, updates are made to the appropriate publishing platform. IRS-III contains publishing platforms to support the publishing of standalone Java and Lisp code and of web services. Web applications (HTTP GET requests) are handled internally by the IRS-III server.
As mentioned above a key design feature of IRS-III is that web service invocation is capability driven. The IRS-III Client supports this by providing a goal-centric invocation mechanism. An IRS-III user simply asks for a goal to be solved and the IRS-III broker locates an appropriate web service semantic description and then invokes the underlying deployed web service.
IRS-III is a framework and implemented infrastructure which allows semantic web service based applications to be created and used. The main features of IRS-III are:
‘One click’ publishing – the provision of interfaces which turn standalone code into a semantic web service,
Capability based invocation – users can ask for goals to be achieved and the IRS-III will locate and execute the appropriate web service, and
Openness – the main components of IRS III are semantic web services which can be overridden to suit a particular context.
As we mentioned earlier we are deploying IRS-III in a number of projects. Our current target domains include eGoverment, semantically enhanced graphical information systems and eLearning. The browser, publisher and Java API for IRS-III can be downloaded from http://kmi.open.ac.uk/projects/irs/.
Benjamins, V. R., Plaza, E., Motta, E., Fensel, D., Studer, R., Wielinga, B., Schreiber, G. and Zdrahal, Z. (1998) An Intelligent Brokering Service for Knowledge-Component Reuse on the World-Wide-Web. In Proceedings of the 11th Workshop on Knowledge Acquisition, Modeling and Management (KAW 98). Banff, Canada.
Crubezy, M., Motta, E., Lu, W. and Musen, M. (2002). Configuring Online Problem-Solving Resources with the Internet Reasoning Service. IEEE Intelligent Systems 2002.
Domingue, J., Cabral, L., Hakimpour, H., Sell, D., and Motta, E. (2004). IRS-III: A Platform and Infrastructure for Creating WSMO-based Semantic Web Services. Proceedings of the Workshop on WSMO Implementations (WIW 2004) Frankfurt, Germany, September 29-30, 2004, CEUR Workshop Proceedings, ISSN 1613-0073 (Available at http://CEUR-WS.org/Vol-113/paper3.pdf).
Feier, C (Ed.) (2004) WSMO Primer, WSMO Deliverable D3.1, DERI Working Draft, 2004.
Fensel, D., Benjamins, V. R., Motta, E. and Wielinga, B (1999) UPML: A Framework for knowledge system reuse. Proceedings of the International Joint Conference on AI (IJCAI-99), Stockholm, Sweden
Fensel, D. and Bussler, C. (2002) The Web Service Modeling Framework WSMF. Electronic Commerce Research and Applications 1(2): 113-137.
Galizia, S. and Domingue, J. (2004) Towards a Choreography for IRS-III. Proceedings of the Workshop on WSMO Implementations (WIW 2004) Frankfurt, Germany, September 29-30, 2004, CEUR Workshop Proceedings, ISSN 1613-0073. (Available at http://CEUR-WS.org/Vol-113/paper7.pdf).
Hakimpour, F., Domingue, J., Motta, E., Cabral, L. and Lei, Y. (2004) Integration of OWL-S into IRS-III, Proceedings of the first AKT Workshop on Semantic Web Services.
Norman, D A. (1988): The Design of Everyday Things. New York, Doubleday
OWL-S (2002) Web Service Description for the Semantic Web. In the Proceedings of The First International Semantic Web Conf. (ISWC), Sardinia (Italy) 2002.
Riva, A. and Ramoni, M. (1996) LispWeb: a Specialised HTTP Server for Distributed AI Applications. Computer Networks and ISDN Systems, 28, 7-11, 953-961.
Roman, D.; Lausen, H.; Keller, U. (2004) The Web Service Modeling Ontology WSMO, Final Version 1.0. WSMO Final Draft D2, 2004. (Available at http://www.wsmo.org/2004/d2/v1.0/).
Roman, D.; Lausen, H.; Keller, U. (2005) The Web Service Modeling Ontology WSMO, Final Version 1.1. WSMO Final Draft D2, 2005. (Available at http://www.wsmo.org/TR/d2/v1.1/).
SOAP (2003) SOAP Version 1.2 Part 0: Primer. (available at http://www.w3.org/TR/soap12-part0/).