Optimizing Web Service Composition While Enforcing Regulations

Abstract

To direct automated Web service composition, it is compelling to provide a template, workflow or scaffolding that dictates the ways in which services can be composed. In this paper we present an approach to Web service composition that builds on work using AI planning, and more specifically Hierarchical Task Networks (HTNs), for Web service composition. A significant advantage of our approach is that it provides much of the how-to knowledge of a choreography while enabling customization and optimization of integrated Web service selection and composition based upon the needs of the specific problem, the preferences of the customer, and the available services. Many customers must also be concerned with enforcement of regulations, perhaps in the form of corporate policies and/or government regulations. Regulations are traditionally enforced at design time by verifying that a workflow or composition adheres to regulations. Our approach supports customization, optimization and regulation enforcement all at composition construction time. To maximize efficiency, we have developed novel search heuristics together with a branch and bound search algorithm that enable the generation of high quality compositions with the performance of state-of-the-art planning systems.

Preference-Based Web Service Composition: A Middle Ground between Execution and Search

“…Several methods can be relevant to a particular nonprimitive task t, leading to different decompositions of t. In our example, the method with name by-air-trans can be used to decompose the task arrange-trans into the subtasks of booking a flight and paying, with the constraint (constr ) that the booking precede payment. Specifying User Preferences and Constraints: Customizing preferences and constraints are specified in a version of PDDL3 that we have augmented to express preferences over how HTN tasks are parameterized and decomposed as well as preferences over service (i.e., task) properties [19,18]. This allows us to combine optimization of service selection (such as quality of service) with optimization of the composition.…”

“…In previous work (e.g., [15,20,19]) we have argued that for a number of WSC problems it is desirable to specify a flexible workflow, generic procedure, or composition template that specifies the basic steps of the composition at an abstract level, but has sufficient flexibility to support their customization for different stakeholders, scenarios, and applications. To this end, we have specified flexible workflows using Golog (e.g., [15,20]), or alternatively Hierarchical Task Networks (HTNs) [19], and developed associated machinery for WSC. We are not alone is proposing such a vision.…”

“…Similarly, in cases where customizations are desirable but not mandatory, customizations can be specified as preferences. This observation has led us to characterize the WSC task as a preference-based planning (PBP) task where actions (services, service parameters, and/or data) are selected not only to achieve the composition objective but to produce compositions that are of high quality with respect to quality of service, trust, or other composition-, service-, or data-oriented user preferences (e.g., [20,11,19,1,10,21]). …”

“…Our investigation is performed in the context of our existing preference-based HTN WSC system, HTNWSC-P [19]. We propose a means of analyzing a WSC problem in order to identify places where optimization can be localized while preserving global optimality.…”

Achieving completeness in the verification of action theories by Bounded Model Checking in ASP

“…[2] exploits a first order linear temporal logic for defining domain dependent search control knowledge in the planner TLPlan, and in [13] strong fairness constraints expressed in LTL are used to restrict nondeterminism in generalized planning. LTL has been used in the verification of agent interaction protocols [24] and for enforcing regulations in automated Web service composition [35]. In the context of reasoning about action, [11] introduced a second order extension of the temporal logic CTL*, ESG, to reason about non-terminating Golog programs.…”