Encoding Web Service Constraints at your Service Coreographies as Constraints

Transcription

1 Encoding Web Service Constraints at your Service Coreographies as Constraints Marco Aiello DIT, University of Trento & DSG, TUWien Joint work with: Mike Papazoglou, Alexander Lazovik, and Rosella Gennari Implementation: Alexander Lazovik, Igor Cappello SRI, June 23 rd, 2006

2 Summary Service Choreography Definition of Choreography framework The XSRL request language The XSAL assertion language An example of a choreography Implementation overiview

3 Problem context and description Given a set of services populating an electronic marketplace that follow standardized business process, equip the requester and service providers with instruments to operate, abstracting from marketplace s s details and avoiding reimplementation as much as possible Choreography: (dynamic) selection and invocation of services in order to achieve requester and providers goals

4 A delicate balance Composition by design vs. Automatic composition design time execution time

5 The orchestration framework

6 Can constraints be of service? Dealing with numeric values Feasibility Notions of optimal solutions Soft constraints to express preferences Dynamic addition and removal of assertions Previous approach using MBP: Advantages: sound and complete algorithms, handling of non-determinism, state together with path properties Disadvantages: state explosion problem, handlling h of numeric values, non-optimality n of the solution

7 Business process for Travelling

8 XSRL: Sample request - 1 Given a business process for a traveling domain, user requests: reserving one night trip to Paris with hotel avoiding to travel by train, if possible spending overall amount less than 300 euros spending less than 100 euros per hotel, if possible, and 200 at most receiving, finally, a confirmation of payment

9 XSRL: language constructs Xml Service Request Language, based on an extension of temporal logic (EaGLe and CTL): achive-all, vital, atomic reachability before then sequencing prefer to, optional preference vital-maint, optional-maint maintainability goals =,<,> linear constraints

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11 XSRL: Sample request - 2 achieve-all before achieve-all prefer vital-maint hotelprice < 100 to vital-maint hotelprice < 200 optional-maint trainbooked vital confirmed ^ location = Paris ^ hotelreserved then atomic final vital-maint price < 300

12 XSAL: Assertion examples - 1 Provider level: Use VISA card for payment, if possible Preserve a positive balance on a bank account Role level: All flights to a health risk countries must have a special medical insurance purchased Travel package entity evolution is checked Process level: Special offer for people with fidelity card (OneWorld( OneWorld) Process must be atomic: always reaching a final state

13 XSAL: Assertions classification Operational assertions Simple Preservation Business Entity VISA card Positive account balance Flight medical insurance Travel package Atomicity Fidelity card Provider Role Business Process Actor assertions (based on ownership)

14 Two Phase Construction Given a BP a request and a set of assertions: PHASE I: encode the BP as a set of constraint expressions PHASE 2: encode the request and assertions based on phase I execute and gather information from service invocations (including varaible values and new assertions)

15 Two Phase Construction Given a BP a request and a set of assertions: PHASE I: encode the BP as a set of constraint expressions PHASE 2: encode the request and assertions based on phase I execute and gather information from service invocations (including varaible values and new assertions)

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17 Phase II

18 Encoding: Completeness Theorem 1. If the service problem P is modeled into the constraint problem E(P), then a solution to the constraint problem corresponds to a solution plan for P.

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20 Encoding the BP

21 A sample request achieve-all vital-maint (price < 155) Vital (Asel = true) Vital (TrConcluded = true) whole encoding and run

22 Implementation and initial evaluation JUnit Eclipse plug-in Implemented using Choco java library with explanation based functionalities GNU-Linux Centrino CPU 2 GHz, RAM 1 GB

23 Preliminary considerations 1. simple reachability requests, domains 2000 states with low branching and non-determisim on an average of 0,947 seconds 2. including cycles the average execution time grows up to 1,737 seconds 3. vital requests, domains 1000 the average execution time increases to 4,29 seconds 4. reachability and maintainability operators the average execution time 10,97 seconds

24 Planning perspective Business process is defined by a state-transition system Problem: find and execute a plan,, such that its execution satisfies the XSRL goal and XSAL assertions From the planning perspective: XSRL & XSAL Service operations Our Framework Business processes Service implementations and registry goal language actions planning domain environment Planning Actions: two types of uncertainty: nondeterministic failures and unknown outcome from the invocations Solution: : interleaved planning and execution

25 Conclusions: summary A language to express user requests XSRL and business rules (assertions) XSAL The Choreography framework: interleaving of planning and execution The realization of the framework using Constraint Programming Advantage of using constraints for Web Services: values, updates, optimality, preferences (soft), explanations An interesting application for contraint programming, beyond traditional scheduling? An implementation of the Choreography framework

26 Conclusions: future directions Properties of the encoding algorithms, e.g., complexity Generalization of the planning in non- determistic domains under uncertainty Implementation of «smart» service selection Use of XSRL and XSAL for expressing QoS properties of requests and assertions Experimental evaluation of the implementation

27 References A. Lazovik, M. Aiello, and R. Gennari, Encoding Requests to Web Service Compositions as Constraints. (2005) LNCS 3709: Constraint Programming (CP 05). A. Lazovik, M. Aiello, and M. Papazoglou, Planning and monitoring the execution of web service requests. (2006) Journal on Digital Libraries,, to appear. M. Aiello, and A. Lazovik, Monitoring assertion-based business processes. (2006) International Journal of Cooperative Information Systems,, to appear.