Towards a Semantic Composition of ebXML Business Processes

Ouassila Hioual LIRE Laboratory, Mentouri University of

Constantine (Algeria)

ouassila.hioual@gmail.com

Zizette Boufaida

LIRE Laboratory, Mentouri University of

Constantine (Algeria)

zboufaida@gmail.com

Abstract

In the Service Oriented Architecture paradigm,

services are self-contained software units of

functionality. Several services can be composed to

assemble a composite one that provides an overall

functionality. This process is called Service

Composition. The automation of the service

composition process aims at decreasing the human

intervention during the service discovery, matching,

filtering and reasoning about the resulting composition

candidates. The paper presents our research work

which consists of the proposition of a new model and

the use of semantic matching technology for semantic

and dynamic composition of ebXML business

processes. For that purpose, we need to enrich ebXML

registries by an OWL-S ontology.

1. Introduction

In the Service Oriented Architecture paradigm, services are self-contained software units of functionality. Several services can be composed to assemble a composite one that provides an overall functionality. This process is called Service Composition. Creating new services by means of composition of existing web services to satisfy a client request is a challenging research issue especially when achieved automatically.

In the literature, there are two approaches of Web-service composition, static composition and dynamic composition [1]. The static one takes place during design-time when the architecture and the design of the software system are planned. The components to be used are chosen, linked together, and finally compiled and deployed. Microsoft Biztalk and Bea WebLogic are examples of static composition engines [17]. Dynamic composition takes place during runtime, i.e. systems can discover and bind Web services dynamically to the application while it’s executing.

Dynamic composition is considered as a good way to deal with and even take advantage of the frequent changes in Web services with minimal user intervention [1].

The dynamic composition of Semantic Web Services requires the location of services based on their capabilities and the recognition of those services that can be matched together to create a composition in a semantic manner. The semantic description of web services makes them interpretable and offers to them a possibility to automatically compose different services for a new composite one. The Ontology Web Language for services OWL-S [10] provides richer semantic specifications with different views of the capabilities of web services. In particular, it provides a functional view of the service as a process which describes both the information transformation which results in the production of outputs from a set of inputs, and the state transformation that results in the generation of effects starting from a state that satisfy preconditions.

In this paper, we present a semantic web services composition architecture. The semantic for service description is based on sub-ontologies and the responsibility of composing and coordinating the execution of a composite service specified by a user is centralised around one component called composer agent. Another agent called the general manager agent is responsible for global control of agents’ tasks. The composer agent is responsible for global control of composition tasks in conjunction with other components called manager agents; it implements many strategies of composition control constructions (sequence, split, If-Then-Else, etc.). We organize the rest of this paper in the following way. In section 2, the overall research problem is introduced. In section 3, the proposed architecture for ebXML BPs composition is presented. Section 4 gives related work. Finally, in section 5, the conclusion and our future work are presented.

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2. Research problem

Our research problem is a part of the semantic and dynamic composition of business processes in the context of ebXML (electronic business eXtensible Markup Language). The goal is to add a component to the functional specification of ebXML, whose role is to:

− Look, semantically, for BPs (Business Processes) that meet the requirements of the client company.

− Combine, semantically, BPs to meet the needs of the client company. This needs i) the definition of an ontology for

ebXML domain, ii) the proposition of a new model and the use of semantic matching technology for semantic and dynamic composition of business processes (web services).

2.1. Where we are locating the new component

ebXML [8] is a set of specifications that together enable a modular electronic business framework. The vision of ebXML is to enable a global electronic marketplace where enterprises of any size and in any geographical location can meet and conduct business with each other through the exchange of XML-based messages.

Figure 01 is an illustration based on the ebXML Technical Architecture Specification [8] which gives an outline of what ebXML means for business.

Figure 1. High-level overview of ebXML interaction between two companies [8]

In Figure 1, Company A has become aware of an ebXML Registry that is accessible on the Internet (Figure 1, step 1). Company A, after reviewing the contents of the ebXML Registry, decides to build and deploy its own ebXML compliant application (Figure 1, step 2). Custom software development is not a necessary prerequisite for ebXML participation [8].

Company A then submits its own Business Profile information (including implementation details and reference links) to the ebXML Registry (Figure 1, step 3). The business profile submitted to the ebXML Registry describes the company’s ebXML capabilities and constraints, as well as its supported business scenarios. These business scenarios are XML versions of the Business Processes and associated information bundles (e.g. a sales tax calculation) in which the company is able to engage. After receiving verification that the format and usage of a business scenario is correct, an acknowledgment is sent to Company A[8] (Figure 1, step 3).

Company B discovers the business scenarios supported by Company A in the ebXML Registry (Figure 1, step 4). Company B sends a request to Company A stating that they would like to engage in a business scenario using ebXML[8] (Figure 1, step 5).

Before engaging in the scenario, Company B submits a proposed business arrangement directly to Company A’s ebXML compliant software Interface. The proposed business arrangement outlines the mutually agreed upon business scenarios and specific agreements. The business arrangement also contains information pertaining to the messaging requirements for transactions to take place, contingency plans, and security related requirements (Figure 1, step 5). Company A then accepts the business agreement. Company A and B are now ready to engage in eBusiness using ebXML (Figure 1, step 6)[8].

In a context of ebXML, all the Business Processes (BPs) of companies (big or small), using ebXML as tool to participate in global markets, are grouped in a Registry/Repository. According to our point of view, the problem of ebXML BPs’ composition appears in two scenarios: 1. When the process looked for with specified

parameters does not exist during the scenario of collaboration between two commercial partners. Combining one ore more services with similar processes can satisfy the needs of the applicant company.

2. When the phase of the parameters negotiation of a business process fails. In order to not stop a possible partnership, a component added to the functional

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specification of ebXML will look for similar BPs and which compose them. This will be based on the history of the negotiation phase.

2.2. Enriching ebXML registries with OWL-S

ontology

To be able to exploit service semantics, service registries should contain not only WSDL (Web Service Description Language) description of the services but also semantic description of the service instances [7].

The popularity of ontologies is rapidly growing since the emergence of the Semantic Web. To date, available Web ontologies continue increasing at a phenomenal rate. For example, Swoogle [6] has collected more than 10,000 ontologies so far.

An ontology is a specification of a shared conceptualization. Therefore, domain experts, users, and designers need to agree on the knowledge specified in ontology so that the ontology may be shared and reused.

Ontologies provide a source of shared and precisely defined terms which can be used to dynamically discover, compose and monitor services. The latter can be represented in different ontology languages such as RDF(S)[3], OWL[12], or formats specific to ontology-development tools, such as Protégé[13] Some ontologies and terminologies are expressed in XML Schema or UML.

Web service semantics is being defined through powerful ontology languages like DAML-S [5] and more recently through OWL-S. In our work, we will use OWL-S to provide the semantics needed for service filtering and composition.

As noted in [11], the principal high-level objectives of OWL-S are (i) to provide a general purpose representational framework in which to describe Web Services; (ii) to support automation of service management and use by software agents; (iii) to build, in an integral fashion, on existing Web Service standards and existing Semantic Web standards; and (iv) to be comprehensive enough to support the entire life cycle of service tasks.

OWL-S is an OWL ontology [4] that includes three primary sub-ontologies: the service profile, process model, and grounding. The service profile is used to describe what the service does; the process model is used to describe how the service is used; and the grounding is used to describe how to interact with the

service. The service profile and process model are thought of as abstract characterizations of a service, whereas the grounding makes it possible to interact with a service by providing the necessary concrete

details related to message format, transport protocol, and so on.

Our solution is inspired from [7] that propose a mechanism of how an ebXML compliant service registry can be augmented with an OWL Service Ontology and how service instance semantics can be used through standardized queries.

2.3. Composition techniques of Web services

Various composition techniques of Web Services exist in the literature. At this stage, there are two big families: the static techniques i.e., which are defined by means of Business Process (orchestration and choreography); and the dynamic ones, in which the composition of Web services takes into account available services, their features and purpose to be reached.

Techniques of dynamic composition can be grouped in two sub-families: techniques using an approach based on workflows (BPs) and those based on techniques on artificial intelligence. In our work, we are interested in the second type of composition in which preferences and constraints of the customers will be considered.

3. Architecture components

Figure 2 depicts the components described in our architecture. The system supports the use of existing e-services able to communicate using standard web services languages.

Figure 2. Architecture Components

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The manager agent ensures that an imported service description is consistent with the sub-ontology that controls in particular the operations, their inputs and outputs names which must be concepts of the sub-ontology. It stores the set of OWL-S services descriptions and the localizations of their e-services providers.

The request constructor agent reconstructs the user request from the descriptions stored in the global BPs ontology. This request which can represent the description of the required composite service is processed by the general manager agent that invokes the composer agent, the latter invokes the manager agents concerned by the request. If the user request concerns an atomic service, the general manager agent invokes the manager agent concerned since it has a global view of the system.

The role of composer agent is to select, coordinate and assemble the manager agents in order to execute the required operations.

3.1. Main tasks involved in the composition of

services

The first task is user request construction. To make that, the user retrieves a special interface. After the user has finish his request construction, we have a request reconstruction step made by the request constructor agent. To reconstruct a request, the request constructor agent retrieves OWL-S available services descriptions that are stored in the global BPs Ontology and which supports both atomic and composite processes.

Once the user request is semantically described, the general manager agent must be able to determine if the user request can be executed by one atomic service or by composing multiple services. In the second case, composer agent must be invoked. The composer agent processes the composite service following the order specified by the user; then it identifies the manager agents that manage the sub-ontologies that publish the required processes. It must be able to perform a matching between the inputs of successive operations and a matching between outputs of an invocation and the inputs of the next required one. In this case, we distinguish several types of compatibility [16] between the parameters. We have Exact match and PlugIn match which represent a total matching, Subsume match and Fail match which give a partial matching. In our model, we consider total matching (“Exact match” and “PlugIn match”). We suppose the compatibility of IOPEs (Inputs, Outputs, Preconditions and Effects) at composition phase. Checking compatibility is made in selection services phase.

4. Related work

Most research efforts handling the Automatic Service Composition have been focusing on the composition of Web Services, e.g. airline ticket booker, hotel finder, translation service, etc. From this perspective the Web Services world is a mash-up of software artefacts developed under a variety of platforms and standards, and a composite web service is the orchestration of various web services to provide a collective functionality.

In the literature, extending ebXML registries with ontology language constructs has been addressed in a few works. A. Dogac et al [7] describe how ebXML registries can be enriched through OWL ontologies to describe Web service semantics. They also describe how the various constructs of OWL can be mapped to ebXML classification hierarchies and how the stored semantics can be queried through standardized queries by using ebXML query facility. However, the only way to store semantic of individual service instances in ebXML registries is done in an extern manner from the “ExtrinsicObject” registry in ebXML terminology. Unfortunately, the content of external objects can not be queried through ebXML queries. If a mechanism to store individual service semantics locally to the registry is developed, then the queries searching for services with required properties can be executed more efficiently [7].

There are different industry efforts to create a standard for web service composition tasks. The Business Process Execution Language for Web Services (BPEL4WS) [4] is one of the most important ones. BPEL4WS provides a language for the formal specification of business processes and business interaction protocols. It extends the interaction model of WSDL to define a process that provides and consumes multiple Web Service interfaces. Such a process can be thought of as composing a set of Web Services from other Web Services. However, BPEL4WS supports static binding of services in the composition, rather than discovering the possibilities on demand.

McIlarith and Son [14] proposed an approach for building agent technology based on the notion of generic procedures and customizing user constraints. They argue that an augmented version of the logic programming language Golog provides a natural formalism for programming Web Services. This version called ConGolog communicates with Web Services via the Open Agent Architecture (OAA), but the service and procedure ontologies are written in first-order logic. To remedy to this problem, in our

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work, the first order logic will be replaced by OWL-S ontology.

5. Conclusion

In this paper, we have presented our research work which consists in enriching ebXML registries by an OWL-S ontology and proposing a new composition model for ebXML Business Processes composition. We have proposed an agent based architecture to will be integrated in the functional specification of ebXML. Our architecture allows defining different responsibility levels. The responsibility of constructing semantically the user request specified by the request constructor agent according to the global BPs ontology, the responsibility of affecting a task to composer agent or directly to manager agent specified by the general manager agent according to its global view of the system, and the responsibility of composing and coordinating the execution of the composite service.

Future work should include all structure agents applied in the architecture especially the compositor one. We will also propose ebXML BPs Ontology by being inspired by works of [7], and classify the latter into a set of sub-ontologies.

References

[1] Baresi, L., Nitto, E.D., and Ghezzi, C., “Toward Open-World Software”. Issues and Challenges, IEEE Computer 39(10), 36–44 (2006)

[2] Berners-Lee, T., and Miller, E., “The Semantic Web lifts off”. ERCIM News N°.51, October 2002.

[3] Brickley, D., and Guha, R.,” Resource Description Framework (RDF) Model and Syntax Specification”. W3C Recommendation submitted 22 February 1999, http://www.w3c.org/TR/1999/REC-rdf-syntax-19990222/(current May 2002).

[4] Curbera, F., Goland, Y., Klein,J., Leymann, F., Roller, D., Thatte, S., and Weerawarana, S., “Business Process Execution Language for Web Services, version 1.0”, July 2001,http://www.106.ibm.com/developerworks/webservices/library/ws-bpel/

[5] DAML Services Coalition. DAML-, “Web Service Description for the Semantic Web”. In The First International Semantic Web Conference (ISWC), June 2002.

[6] Ding, L., Pan, R., Finin, T., Joshi, A., Peng, Y., and Kolari, P., “Finding and ranking knowledge on the Semantic Web”. In: Gil, Y., Motta, E., Benjamins, V.R., Musen, M.A. (eds.) ISWC 2005. LNCS, vol. 3729, pp. 156–170. Springer, Heidelberg (2005).

[7] Dogac, A., Kabak, Y., and Laleci, G. B., “Enriching ebXML Registries with OWL Ontologies for Efficient Service Discovery”. This work is supported by the

Scientific and Technical Research Council of Turkey, Project No: EEEAG 102E035.

[8] ebXML, http://www.ebXML.org/specs/ebTA.pdf[9] Horrocks, I., van Harmelen, F., Patel-schneider, P.,

Berners-Lee, T., Brickley, D., Connoly, D., Dean, M., Decker, S., Fensel, D., Hayes, P., Heflin, J., Hendler, J., Lassila, O., McGuinness, D., and Stein, L. A., “DAML+OIL”, 2001. http://www.daml.org/2001/03/daml+oil-index.html/.

[10] Martin, D., Burstein, M., Hobbs, J., Lassila, O., McDermott, D., and McIlraith, S., “OWL-S: Semantic Markup for Web Services”. W3C Member Submission 22 November2004,http://www.w3.org/Submission/2004/SUBM-OWL-S-20041122/

[11] Martin, D., Burstein, M., McDermott, D., McIlraith, S., Paolucci, M., Sycara, K., McGuinness, D.L., Sirin, E., and Srinivasan, N., “Bringing Semantics to Web Services with OWL-S. World Wide Web 10(3)” (September 2007)

[12] McGuinness, D. L., and van Harmelen, F., “OWL Web Ontology Language Overview”. W3C Recommendation 10 Ferbruary 2004, http://www.w3.org/TR/2004/REC-owl-features-20040210.

[13] McGuinness, D.L., and van Harmelen, F., “O.W.L: Ontology Language Overview”, W3C Recommendation (February 10, 2004), http://www.w3.org/TR/2004/REC-owl-features- 20040210/

[14] McIlarith, S., and Son, T., “Adapting Golog for Composition of Semantic Web Services”. In Conference on Knowledge Representation and Reasoning, April 2002.

[15] Protégé, http://protege.stanford.edu[16] Serin, E., Parsia, B., and Hendler, J., “Composition

driven Filtering and Selection of semantic Web sevices”. In AAAI Spring Symposium on Semantic Web Services, 2004.

[17] Sun, H., Wang, X., Zhou, B., and Zou, P., “Research and Implementation of Dynamic Web Services Composition”. In: Zhou, X., Xu, M., Jähnichen, S., Cao, J. (eds.) APPT 2003. LNCS, vol. 2834, pp. 457–466. Springer, Heidelberg (2003)

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