Towards Automatic Non-Deterministic Web Service Composition

Towards Automatic Non-Deterministic Web Service Composition
Markou, G. & Refanidis, I. Dept. of Applied Informatics, University of Macedonia, Greece ICIW Web Services-based Systems & Applications IV

ICIW 2012 - Web Services-based Systems & Applications IV
In Summary Introduction Related Work Method of Choice Use of Standards Online Evaluation Proposed Approach Quantitative criteria Use case scenarios Conclusion Application Registry Web Service Editor Translation between AI & Web Service languages Manual Web Service Composition module Automatic Web Service Composition module Work in progress Implementation of an online Web Service Composition system Based on the most prevalent Web Service standards Utilizing other open source projects as sub-elements Treats non-determinism as an inherent characteristic of the problem  tackles it by exploiting AI planning, specifically contingency planning Detailed use case scenarios to evaluate WSC systems’ capabilities ICIW Web Services-based Systems & Applications IV

Introduction Related Work Method of Choice Use of Standards Online Evaluation Proposed Approach Application Registry Web Service Editor Translation between AI & Web Service languages Manual Web Service Composition module Automatic Web Service Composition module Quantitative criteria Use case scenarios Conclusion Work in progress Implementation of an online Web Service Composition system Based on the most prevalent Web Service standards Utilizing other open source projects as sub-elements Treats non-determinism as an inherent characteristic of the problem  tackles it by exploiting AI planning, specifically contingency planning Detailed use case scenarios to evaluate WSC systems’ capabilities ICIW Web Services-based Systems & Applications IV

Motivation Difficult to expect from a human user /experts to manually complete the goal of a Web Service Composition (WSC) Number of Web Services (WSs) is growing continuously  discovery phase more difficult Ever-changing environment: WSs can change interfaces or even part of their usage multiple times throughout their lifespan Always possible that their execution is not successful ICIW Web Services-based Systems & Applications IV

System Goals - Functionalities:
Online Registry / Advertisement / Semantic search of Web Services Editing of Web Services Translation/ mapping between AI & Web Service languages Manual Web Service composition module Automatic Web Service composition module Evaluation based on Quantitative criteria Use case scenarios ICIW Web Services-based Systems & Applications IV

Method of Choice (1/2) Method of choice? Use of standards? Most widespread: AI planning Diverse OWL-S / PDDL widely used Other standards (e.g., WSMO) Proprietary formats Perhaps most notable is Sirin, et al. (2004) From WSC problem (described in OWL-S) to HTN Composite process that can be decomposed to simpler ones Simple processes being atomic WSs Reduces complexity of the planning process  Cannot cope with non-determinism  Planner-dependent  E. Sirin, B. Parsia, D. Wu, J. Hendler, and D. Nau, “HTN planning for web service composition using SHOP2”, J. Web Semant., vol. 1, no. 4, Oct. 2004, pp Available WSs’ OWL-S process models are translated to a SHOP2 domain, and the WSC problem to a compatible HTN planning problem by describing it as a composite process that can be decomposed to simpler ones (with simple processes being atomic WSs). Then, the planner generates a plan that can be converted back to an OWL-S process and executed by OWL-S API. SHOP2 plans for tasks in the same order in which they will be executed, which allows it to be aware of the current state of the world at each step. In that way it can gain significant reasoning power in regard to its precondition-evaluation mechanism and reduce the complexity of the planning process. ICIW Web Services-based Systems & Applications IV

Method of Choice (2/2) AI planning also used in Hoffmann, et al. (2009) Treats the application of a WS as a belief update operation Identifies tractable special cases of WSC Allow for a compilation into planning under uncertainty  Subsequent use of existing conformant planner  PDDL-like problem descriptions  No standardized WS description  J. Hoffmann, P. Bertoli, M. Helmert, and M. Pistore, “Message-based web service composition, integrity constraints, & planning under uncertainty: a new connection”, J. Artif. Intell. Res, vol. 35, May 2009, pp it identifies two special cases of WSC that are more tractable and allow for a compilation into planning under uncertainty and the subsequent use of an already existing conformant planner (Conformant-FF) ICIW Web Services-based Systems & Applications IV

Use of Standards Klusch, Gerber & Schmidt (2005) and Hatzi, et al. (2011) rely on translation of OWL-S descriptions to PDDL problems  Klusch, Gerber & Schmidt (2005): Outputs modified PDDL files (in XML)  Does not have evaluation on WSC problems  Hatzi, et al. (2011) tackles uncertainty with re-planning module  Both only address WSC problem, not other stages  PDDL and OWL-S are, as we will talk about later on, respectively, the de facto planning language and the most widely used semantic description language M. Klusch, Α. Gerber, and M. Schmidt, “Semantic web service composition planning with OWLS-Xplan”, Proc. 1st International AAAI Fall Symposium on Agents and the Semantic Web, Nov. 2005 OWLS-Xplan translates OWL-S descriptions to corresponding PDDL 2.1 ones Does not output a standard PDDL file, but a modified version of it in XML, which, according to the authors, simplifies parsing, reading, and communicating PDDL descriptions using SOAP. Then, Xplan, a hybrid planner that combines guided local search with graph planning and a simple form of HTN decomposition, is called to solve the planning problem. O. Hatzi, D. Vrakas, M. Nikolaidou, et al., “An integrated approach to automated semantic web service composition through planning”, IEEE Trans. Service Computing, April 2011, pp Can use two alternative external PDDL planners to obtain a solution ICIW Web Services-based Systems & Applications IV

Online YaWSA (Macdonald, 2007) Only web-based WSC system in literature with running demo  Only implemented a WSC process (no registry, view WSs’, etc) No longer available for public use  Prototype web-based WSC system described in Du, Song, and Munro (2006) Supporting multiple phases of WSC  Public link to running demo of their implementation is not provided  A. Macdonald, “Service composition with hyper-programming”. Technical Report, University of St Andrews, 2007 X. Du, W. Song, and M. Munro, “Using common process patterns for semantic web services composition”, Proc. 15th International Conference on Information Systems Development (ISD’06), Sept supporting WS browsing creation of composite services service flow execution generation of OWL-S descriptions used for describing their common process pattern instances. These instances are meant to bridge the gap between the users’ requirements and the technical service descriptions, as the authors consider OWL-S to be insufficient and not abstract enough to achieve such a result on its own. ICIW Web Services-based Systems & Applications IV

Evaluation Literature suggests a gap in the evaluation process of the current WSC systems Many simply evaluate their methodology on a single case study, without referring to quantitative criteria, e.g., Chen, Xu, and Reiff-Marganiec (2009), McDermott (2002), McIlraith and Son (2002) Notable exceptions: Hoffmann, et al. (2009) : Two artificial benchmarks with different encodings and planners Hatzi, et al. (2011): Single use case, with different number of WSs Test collection combination of hand-tailored atomic WSs and entire domains of OWL-S Service Retrieval Test Collection (OWL-S TC) Kona, et al. (2008): Three versions of a single use case, each suited for a mode of their WSC algorithm Test collection: Modified version of the 2006 WS-Challenge K. Chen, J. Xu, and S. Reiff-Marganiec, “Markov-HTN planning approach to enhance flexibility of automatic web service composition”, 2009, pp. 9-16 D.V. McDermott, “Estimated-regression planning for interactions with web services”, 2002, pp S. McIlraith and T. Son, “Adapting Golog for composition of semantic web services”, 2002, pp O. Hatzi, D. Vrakas, M. Nikolaidou, et al., “An integrated approach to automated semantic web service composition through planning”, IEEE Trans. Service Computing, April 2011, pp measuring the preprocessing, transformation (from OWL-S to PDDL) and planning time required. However, the use of only one planner is referenced, despite the possible use of two different ones, and the atomic WSs that comprise the composite one seem to be (mostly) hand-tailored by the authors J. Hoffmann, P. Bertoli, M. Helmert, and M. Pistore, “Message-based web service composition, integrity constraints, & planning under uncertainty: a new connection”, 2009, pp two artificial benchmarks with different encoding methods and planners, and measures the total runtime of the planner, as well as the number of search states and actions in the output plans S. Kona, A. Bansal, M.B. Blake, and G. Gupta, “Generalized Semantics-Based Service Composition”. 2008 Sequential Composition Non-Sequential Composition Non-Sequential Conditional Composition quantitative results regarding the number of WSs participating in the WSC the number of I/O parameters each WS had the preprocessing and query execution time needed to obtain a solution do not provide details regarding the machine that was used to run the experiments. ICIW Web Services-based Systems & Applications IV

Proposed Approach - Application
User registration Ext GWT (GXT) external library for UI widgets Based on Google Web Toolkit (GWT): Initial screen ICIW Web Services-based Systems & Applications IV

Registry (1/2) Core of the application is based on iServe Open platform for publishing and discovering services WSs are semantically described in OWL-S, not Minimal Service Model Used its web-based application for Browsing Querying Uploading services Populated the registry with version 4.0 of OWL-S TC Made several improvements to its interface and functionality iServe translates all services uploaded to a model of its own, called Minimal Service Model (MSM), which is a simple RDF(S) ontology able to capture (part of) the semantics of both Web services and Web APIs in a common model ICIW Web Services-based Systems & Applications IV

Registry (2/2) Inline operations Web Service details Semantic search alternatives ICIW Web Services-based Systems & Applications IV

Proposed Approach – WS Editor
XML Editor with syntax highlighting Pre-defined OWL-S templates We modified GWT-codemirror to create an XML editor of our own ICIW Web Services-based Systems & Applications IV

Translation between AI & WS Languages
AI planning language: PDDL, the de facto planning language Specifically, NuPDDL Compatible with PDDL2.1, retaining most of it Capable of modeling non-deterministic action effects (one of, unknown) WS semantic description language: OWL-S, most widely used Heavily influenced from planning languages, such as PDDL Partial mapping from OWL-S to PDDL exists Part of it straightforward: ServiceProfile input parameters  identically named ones of PDDL action hasPrecondition/ hasEffect parameters precondition/ effect of action Conversion of non-physical knowledge from OWL-S to PDDL problematic  Introduction of new predicate in PDDL domain? NuPDDL: compatible with PDDL2.1, retaining most of it, including the handling of functions, conditional effects, and quantifiers The language used by Model Based Planner (MBP), a system designed to perform plan synthesis, plan validation and plan/domain simulation in non-deterministic domains In the current NuPDDL version, the following restrictions apply: - every object/function must be typed - no nested functions is allowed - axioms are not handled Both tackle the problem by introducing a new predicate in the PDDL domain; the first creates a predicate agentKnows with one argument that can either be bound to an input or an output parameter the second adds every output variable X to the world state through the introduction of an add-effect predicate agentHasKnowledgeAbout(X) (the same process is followed in an analogous manner for every input parameter) ICIW Web Services-based Systems & Applications IV

Manual WSC Module Under implementation Based on PetalsBPM Modification from BPMN 2.0 editor to suit OWL-S WSC functionalities To be compared with automatic WSC module (ease of use, speed, etc) ICIW Web Services-based Systems & Applications IV

Automatic WSC Module Future work – Basic directions: WSs may fail to execute correctly, e.g., Unavailability of an atomic WS involved in the plan Output of their successful execution is not the expected one Generate plans tackling the most influential and likely contingencies Proposed solution based on contingent planning Produce seed plan Examine for significant/ likely points of failure Add conditional branches Re-planning module will be integrated this process will be repeated until we either reach a plateau or run out of time. As we cannot cope with every possible point of failure, a re-planning module will also be incorporated. convert the NuPDDL plan back to an OWL-S (composite) WS, that is, create an OWL-S profile and its process description, without, however, providing a corresponding WSDL definition In short, the profile description of the new composite WS will treat it as an atomic service with IOPEs, while the process model will be based on OWL-S control constructs that describe the way the WSs that compose the composite one interact with each other. OWL-S API will be used to implement the conversion supports composite processes ICIW Web Services-based Systems & Applications IV

Quantitative Criteria
Criteria to be considered: Number of Web Services considered for WSC Preprocessing time (parsing of ontologies’ concepts, etc) Transformation time (of WS domain to PDDL one) Planning time (to output a successful plan) Optimality of the outputted plans (least WSs used to achieve the required goal) ICIW Web Services-based Systems & Applications IV

Use Case Scenarios Based on OWL-S TC Semantic Web Services v. 4.0 (PDDL) Each scenario uses a subset of descriptions of an OWL-S TC domain A few semantic WS descriptions were added for testing purposes, and some were modified Each scenario with increasing non-determinism & complexity ICIW Web Services-based Systems & Applications IV

Movie Database Scenario (1/2)
Movie database search using a (partial) movie title Based on Communication domain: 58 semantic WSs in total Fully deterministic - Serialized composite WS output Retrieve comedy films with titles similar to user input Output: Movie titles Pricing information (tax-free price, recommended price, etc) ICIW Web Services-based Systems & Applications IV

Movie Database Scenario (2/2)
Composite Web Service (created through Manual WSC module) ICIW Web Services-based Systems & Applications IV

Online Bookstore Scenario (1/2)
Online bookstore product purchase User wants to purchase a book from an specific online bookstore with a preferred method of payment Preferences regarding method of payment Based on Education domain: 285 semantic WSs in total Non-deterministic output Different outcomes: Output if book in stock: Addition of book in shopping cart Purchase with the specified method of payment Output information regarding it, such as its author No output if book not in stock a preferred method of payment (a cheque, debit or credit card) If, however, it is not in stock, no payment should be made, and no further information concerning it should be displayed to the client ICIW Web Services-based Systems & Applications IV

Online Bookstore Scenario (2/2)

Camera Search Scenario (1/2)
Camera search and purchase User want to purchase an analog SLR model; willing to settle for other ones if it is not in stock User preference towards specific model More than one sellers exist Based on Economy domain: 359 semantic WSs in total Possible iteration in output Web Service Since more than one sellers exist, if product not available at one, check another If product not found in any of the sellers, try with other versions (digital SLR, simple compact cameras) As such, if a store is found that sells the analog SLR model and has it in stock, it should be added to the user’s shopping cart. If it is not in stock, the search should continue for another store that sells it, and if one cannot be found, the process should be repeated, this time searching for the camera’s compact version, or, if all else fails, for any camera available in stock ICIW Web Services-based Systems & Applications IV

Camera Search Scenario (2/2)

Conclusion Current WSC approaches, in general: Do not deal with inherent non-determinism in WSC domain Are not online, despite WS’ use & nature being web-oriented Do not evaluate their methodology using well defined scenarios or test sets Improvements have been made recently Our final system is intended to be the first online and open source system supporting multiple phases of WSC Presented scenarios provide efficient way of evaluation Can be used by other WSC works as a common test bed Although the first two scenarios can be considered as special cases of the last one, it is important to showcase that the system can indeed cope with the generation of both sequential and conditional plans, with and without preferences. Moreover, the importance of the scenarios lies in that they exhibit that this particular test set can be used to produce meaningful use cases that can evaluate the capabilities of WSC approaches efficiently and in a manner that is reproducible and extensible. ICIW Web Services-based Systems & Applications IV

Thank you for your attention!
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References: Referenced papers: E. Sirin, B. Parsia, D. Wu, J. Hendler, and D. Nau, “HTN planning for web service composition using SHOP2”, J. Web Semant., vol. 1, no. 4, Oct. 2004, pp J. Hoffmann, P. Bertoli, M. Helmert, and M. Pistore, “Message-based web service composition, integrity constraints, and planning under uncertainty: a new connection”, J. Artif. Intell. Res, vol. 35, May 2009, pp M. Klusch, Α. Gerber, and M. Schmidt, “Semantic web service composition planning with OWLS-Xplan”, Proc. 1st International AAAI Fall Symposium on Agents and the Semantic Web, Nov O. Hatzi, D. Vrakas, M. Nikolaidou, et al., “An integrated approach to automated semantic web service composition through planning”, IEEE Trans. Service Computing, April 2011, pp A. Macdonald, “Service composition with hyper-programming”. Technical Report, University of St Andrews, X. Du, W. Song, and M. Munro, “Using common process patterns for semantic web services composition”, Proc. 15th International Conference on Information Systems Development (ISD’06), Sept K. Chen, J. Xu, and S. Reiff-Marganiec, “Markov-HTN planning approach to enhance flexibility of automatic web service composition”, Proc. IEEE International Conference on Web Services (ICWS'09), July 2009, pp D.V. McDermott, “Estimated-regression planning for interactions with web services”, Proc. Sixth International Conference on Artificial Intelligence Planning Systems (AIPS ’02), April 2002, pp S. McIlraith and T. Son, “Adapting Golog for composition of semantic web services”, Proc. 8th International Conference on Principles of Knowledge Representation and Reasoning (KR2002), April 2002, pp S. Kona, A. Bansal, M.B. Blake, and G. Gupta, “Generalized Semantics-Based Service Composition”, Proc. IEEE International Conference on Web Services (ICWS’08), Sept Details about the system presented: Source code available – Pre-alpha: Check paper for link Full description of the use cases & the WSs they are based on : Check paper for link ICIW Web Services-based Systems & Applications IV

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