Web Service Composition via Generic Procedures and Customizing User Preferences

Abstract. We claim that a key component of effective Web service composition, and one that has largely been ignored, is the consideration of user preferences. In this paper we propose a means of specifying and intergrating user preferences into Web service composition. To this end, we propose a means of performing automated Web service composition by exploiting generic procedures together with rich qualitative user preferences. We exploit the agent programming language Golog to represent our generic procedures and a first-order preference language to represent rich qualitative temporal user preferences. From these we generate Web service compositions that realize the generic procedure, satisfying the user’s hard constraints and optimizing for the user’s preferences. We prove our approach sound and optimal. Our system, GologPref, is implemented and interacting with services on the Web. The language and techniques proposed in this paper can be integrated into a variety of approaches to Web or Grid service composition.

HTN planning: Overview, comparison, and beyond

Hierarchies are one of the most common structures used to understand and conceptualise the world. Within the field of Artificial Intelligence (AI) planning, which deals with the automation of world-relevant problems, Hierarchical Task Network (HTN) planning is the branch that represents and handles hierarchies. In particular, the requirement for rich domain knowledge to characterise the world enables HTN planning to be very useful, and also to perform well. However, the history of almost 40 years obfuscates the current understanding of HTN planning in terms of accomplishments, planning models, similarities and differences among hierarchical planners, and its current and objective image. On top of these issues, the ability of hierarchical planning to truly cope with the requirements of real-world applications has been often questioned. As a remedy, we propose a framework-based approach where we first provide a basis for defining different formal models of hierarchical planning, and define two models that comprise a large portion of HTN planners. Second, we provide a set of concepts that helps in interpreting HTN planners from the aspect of their search space. Then, we analyse and compare the planners based on a variety of properties organised in five segments, namely domain authoring, expressiveness, competence, computation and applicability. Furthermore, we select Web service composition as a real-world and current application, and classify and compare the approaches that employ HTN planning to solve the problem of service composition. Finally, we conclude with our findings and present directions for future work. In summary, we provide a novel and comprehensive viewpoint on a core AI planning technique.<br/

Quantifiable non-functional requirements modeling and static verification for web service compositions

As service oriented architectures have become more widespread in industry, many complex web services are assembled using independently developed modular services from different vendors. Although the functionalities of the composite web services are ensured during the composition process, the non-functional requirements (NFRs) are often ignored in this process. Since quality of services plays a more and more important role in modern service-based systems, there is a growing need for effective approaches to verifying that a composite web service not only offers the required functionality but also satisfies the desired NFRs. Current approaches to verifying NFRs of composite services (as opposed to individual services) remain largely ad-hoc and informal in nature. This is especially problematic for high-assurance composite web services. High-assurance composite web services are those composite web services with special concern on critical NFRs such as security, safety and reliability. Examples of such applications include traffic control, medical decision support and the coordinated response systems for civil emergencies. The latter serves to motivate and illustrate the work described here. In this dissertation we develop techniques for ensuring that a composite service meets the user-specified NFRs expressible as hard constraints, e.g., the messages of particular operations must be authenticated. We introduce an automata-based framework for verifying that a composite service satisfies the desired NFRs based on the known guarantees regarding the non-functional properties of the component services. This automata-based model is able to represent NFRs that are hard, quantitative constraints on the composite web services. This model addresses two issues previously not handled in the modeling and verification of NFRs for composite web services: (1) the scope of the NFRs and (2) consistency checking of multiple NFRs. A scope of a NFR on a web service composition is the effective range of the NFR on the sub-workflows and modular services of the web service composition. It allows more precise description of a NFR constraint and more efficient verification. When multiple NFRs exist and overlap in their scopes, consistency checking is necessary to avoid wasted verification efforts on conflicting constraints. The approach presented here captures scope information in the model and uses it to check the consistency of multiple NFRs prior to the static verification of web service compositions. We illustrate how our approach can be used to verify security requirements for an Emergency Management System. We then focus on families of highly-customizable, composed web services where repeated verification of similar sets of NFRs can waste computation resources. We introduce a new approach to extend software product line engineering techniques to the web service composition domain. The resulting technique uses a partitioning similar to that between domain engineering and application engineering in the product-line context. It specifies the options that the user can select and constructs the resulting web service compositions. By first creating a web-service composition search space that satisfies the common requirements and then querying the search space as the user makes customization decisions, the technique provides a more efficient way to verify customizable web services. A decision model, illustrated with examples from the emergency-response application, is created to interact with the customers and ensure the consistency of their specifications. The capability to reuse the composition search space is shown to improve the quality of the composite services and reduce the cost of re-verifying the same compositions. By distinguishing the commonalities and the variabilities of the web services, we divide the web composition into two stages: the preparation stage (to construct all commonalities) and the customization stage (to choose optional and alternative features). We thus draw most of the computation overhead into the first stage during the design in order to enable improved runtime efficiency during the second stage. A simulation platform was constructed to conduct experiments on the two verification approaches and three strategies introduced in this dissertation. The results of these experiments were analyzed to show the advantage of our automaton-based model in its verification efficiency with scoping information. We have shown how to choose the most efficient verification strategy from the three strategies of verifying multiple NFRs introduced in this dissertation under different circumstances. The results indicate that the software product line approach has significant efficiency improvement over traditional on-demand verification for highly customizable web service compositions

AUTOMATED COMPOSITION OF WEB SERVICES VIA PLANNING IN ASYNCHRONOUS DOMAINS\ud

The service-oriented paradigm promises a novel degree of interoperability between\ud business processes, and is leading to a major shift in way distributed applications are\ud designed and realized. While novel and more powerful services can be obtained, in such\ud setting, by suitably orchestrating existing ones, manually developing such orchestrations\ud is highly demanding, time-consuming and error-prone. Providing automated service\ud composition tools is therefore essential to reduce the time to market of services, and\ud ultimately to successfully enact the service-oriented approach.\ud In this paper, we show that such tools can be realized based on the adoption and extension\ud of powerful AI planning techniques, taking the “planning via model-checking” approach\ud as a stepping stone. In this respect, this paper summarizes and substantially extends a\ud research line that started early in this decade and has continued till now. Specifically, this\ud work provides three key contributions.\ud First, we describe a novel planning framework for the automated composition of Web\ud services, which can handle services specified and implemented using industrial standard\ud languages for business processes modeling and execution, like ws-bpel. Since these\ud languages describe stateful Web services that rely on asynchronous communication\ud primitives, a distinctive aspect of the presented framework is its ability to model and\ud solve planning problems for asynchronous domains.\ud Second, we formally spell out the theory underlying the framework, and provide algorithms\ud to solve service composition in such framework, proving their correctness and\ud completeness. The presented algorithms significantly extend state-of-the-art techniques\ud for planning under uncertainty, by allowing the combination of asynchronous domains\ud according to behavioral requirements.\ud Third, we provide and discuss an implementation of the approach, and report extensive\ud experimental results which demonstrate its ability to scale up to significant cases for\ud which the manual development of ws-bpel composed services is far from trivial and time\ud consuming

Methods for Efficient and Accurate Discovery of Services

With an increasing number of services developed and offered in an enterprise setting or the Web, users can hardly verify their requirements manually in order to find appropriate services. In this thesis, we develop a method to discover semantically described services. We exploit comprehensive service and request descriptions such that a wide variety of use cases can be supported. In our discovery method, we compute the matchmaking decision by employing an efficient model checking technique