Composition of Semantic Web Services using Linear Logic Theorem Proving Jinghai Rao a Peep K¨ungas a Mihhail Matskin b aDepartment of Computer and Information Science, Norwegian University of Science and Technology, NO-7491, Trondheim, Norway, Email: {jinghai,peep}@idi.ntnu.no bDepartment of Microelectronics and Information Technology, Royal Institute of Technology, SE-164 40 Kista, Sweden, Email: [email protected] Abstract This paper introduces a method for automatic composition of Semantic Web services using Linear Logic (LL) theorem proving. The method uses a Semantic Web service language (DAML- S) for external presentation of Web services, while, internally, the services are presented by extralogical axioms and proofs in LL. LL, as a resource conscious logic, enables us to define attributes of Web services formally (including parameters, states and non-functional attributes). We use a process calculus to present the process model of the composite service formally. The process calculus is attached to the LL inference rules in the style of type theory. Thus the process model for a composite service can be generated directly from the complete proof. The subtyping rules that are used for semantic reasoning are presented with LL inference figures. We propose a system architecture where the DAML-S Translator, LL Theorem Prover and Semantic Reasoner can operate together. This architecture has been implemented in Java. Key words: Service composition, Web service, Semantic Web 1 Introduction ment to the Web service provision. In particular, if no single Web service can satisfy the functionality required by the Recent progress in the field of Web ser- user, there should be a possibility to com- vices makes it practically possible to bine existing services together in order publish, locate, and invoke applications to fulfill the request. This trend has trig- across the Web. This is a reason why more gered a considerable number of research and more companies and organizations efforts on Web services composition both now implement their core business and in academia and in industry. outsource other application services over Internet. The ability to efficient selection Several Web service initiatives provide and integration of inter-organizational platforms and languages that should al- and heterogeneous services on the Web at low easy integration of heterogeneous runtime becomes an important require- systems. In particular, Universal De- Preprint submitted to Elsevier Science 13 June 2004 scription, Discovery, and Integration sition of atomic services that satisfies the (UDDI) [7], Web Services Description user requirements. The reason why we use Language (WSDL) [11], Simple Object LL theorem proving as Web service com- Access Protocol (SOAP) [8] and parts of position method is that LL is resource- DAML-S [25] ontology (including Servi- conscious logic. This means that, first, we ceProfile and ServiceGrounding) define can distinguish the information transfor- standard ways for service discovery, de- mation and the state change produced by scription and invocation (message pass- the Web service and, second, we can per- ing). Some other initiatives including form planning using both qualitative and Business Process Execution Language quantitative non-functional attributes. for Web Services (BPEL4WS) [4] and Because of soundness of the logic frag- DAML-S ServiceModel, are focused on ment used the correctness of composite representing service compositions where services is guaranteed with respect to the a process flow and bindings between ser- initial specifications. Completeness of the vices are known a priori. logic fragment ensures that all compos- able solutions would be found. The problem of Web service composition is a highly complex task. Here we under- Secondly, we present a composition ap- line only the following two sources of its proach that allows reasoning with types complexity. Firstly, Web services can be from a service specification. We introduce created and updated on the fly, and it may a set of subtyping rules that defines a valid be beyond human capabilities to analyze dataflow for composite services. The sub- a huge amount of available services and typing relationships between the DAML to compose them manually. Secondly, the concepts are detected by the Semantic Web services are usually developed by dif- Reasoner separately from the LL Theo- ferent organizations that use different se- rem Prover. Since the rules are defined as mantic model presenting services’ charac- logical implications, the interoperability teristics (for example, non-functional at- is ensured between the Linear Logic The- tributes) and this requires utilization of orem Prover and the Semantic Reasoner. relevant semantic information for match- ing and composition of Web service. Web service composition using theorem proving is a relatively new topic, and it In this paper, we propose a solution that has been mentioned in quite recent pub- allows decreasing the complexity of the lications. However, the idea of software Web service composition task emerging construction from proofs is not new. In from the above-mentioned sources. particular, deductive program synthesis is based on an observation that constructive Firstly, we present a method for auto- proofs are equivalent to programs where mated Web service composition which is each step of a proof can be interpreted as based on the proof search in a fragment a step of a computation. The key ideas of propositional Linear Logic (LL) [14]. of the software composition approach, as The main idea of the method is as fol- well as correspondence between theorems lows. Given a set of existing Web services and specifications and between construc- and the requirements in term of DAML-S tive proofs and programs, are presented ServiceProfile, the method finds a compo- in [23]. 2 There is still a long way towards com- tation and extralogical axioms in LL. plete automation of service composition In our system, DAML-S ServicePro- in a general case. In this paper we re- file is used externally for presentation strict the problem to composition of value- of atomic Web service specifications, added services only assuming that a core while LL axioms are used internally service (atomic or composed) already ex- for composition. The process model is ists. internally presented by a process cal- culus. The calculus can be translated The rest of this paper is organized as either into DAML-S ServiceModel or follows: Section 2 describes a system ar- BPEL4WS. chitecture for composition of Semantic GUI: visualizes services (both com- Web services, Section 3 gives a motivat- posed and atomic). The graphical ing example. Section 4 presents back- presentation includes visualization of ground knowledge for service description functionalities and non-functional at- language and LL. Section 5 presents a tributes. method for transformation of DAML-S LL Theorem Prover: proves whether profile to extralogical axioms in LL lan- the user’s request for service can be guage. Section 6 discusses the usage of achieved by a composition of the avail- type system to enable semantic compo- able atomic services. If the answer is sition. Section 7 presents the implemen- yes, the process model for the compos- tation of a prototype system. Finally, ite service is automatically extracted related works and conclusions are pre- from the proof. sented. Semantic Reasoner: detects the sub- typing and some other relationships between concepts in service descrip- 2 The service composition archi- tions. The formal logics used in Seman- tecture tic Reasoner could be logics developed for expressing knowledge and reasoning about concepts and concept hierarchies, A general architecture of the proposed for example, Description Logics [15]. Web service composition system is de- A transformation between Description picted on Figure 1. The system takes Logics and LL is done by the Adapter. available atomic services and user’s re- Adapter: performs translation between quirements (both of them are described LL and the internal presentation used in DAML-S ServiceProfile and grounded by the Semantic Reasoner. by WSDL documents) as inputs and pro- duces a set of possible composite services The composition process in our case is presented by the ServiceModel in DAML- as follows. Firstly, a semantic descrip- S service model or BPEL4WS. tion of existing Web services (in the form of DAML-S ServiceProfile) is translated The basic components of the system are into extralogical axioms of LL and the the follows: user’s request for a composite service is specified in the form of a LL sequent to Translator: performs automated trans- be proven. Then, the LL Theorem Prover formation between an external presen- checks whether the request can be satis- 3 Service Profile Extralogical Axioms Linear Logic Translator Theorem Prover Proof Service Process l C a mI S las n se le p e s tio b il m an i a c a d P s i a n ro o r it t pe p a o ci rtie ro V n s P GUI Adapter R S y l e u g e al b lo d t yt to o oi p n M n ni O s g Semantic Ontology Reasoner Base Fig. 1. The architecture of the service composition system. fied by a composition of existing atomic lar, they may stand alone in terms of op- services (this is done by applying theo- eration and profitability as well as pro- rem proving in LL). During the theorem vide adds-on to core services. It is impor- proving the Theorem Prover may inter- tant to mention that value-added services act with the Semantic Reasoner. As a may allow different their combination and result of this interaction the Semantic they may provide incremental extension of Reasoner may provide extensions of the core services. For example, in online shop- set of extralogical axioms via performing ping, the core services range from prod- subtyping inference using Ontology Base. uct search, ordering, payment and ship- New axioms are asserted into the Theo- ment.