Modelling and Analysis of Time-related Properties in Web Service Compositions

1. Modelling and Analysis of Time-relatedProperties in Web Service Compositions

2. Problem in Hands • Service composition as a way to obtain new functionality by combining existing services into distributed business processes • re-usage of existing heterogeneous applications • stack of standards (e.g. BPEL) for different aspects of WS compositions (e.g. behavior) • Analyze correctness of the WS composition • quantitative properties (deadlocks, livelocks, LTL properties) • qualitative properties (performance, time, resource allocation) • Time-related properties are particularly relevant • necessity to support Long-Running Transactions • compatibility of time-consuming tasks w.r.t. the expected timing constraints • compatibility of local timed commitments of different involved parties WESC'05

3. Case Study: e-Government Application • Domain: Environmental Protection Agency authorization for the establishment and operation of a waste disposal or recycling plant • Settings: complex distributed process involving various actors • state authorities (province board) • local public services (agencies, administrations, secretaries) • consultants and experts (environmental engineers) • process clients (companies, information requestors) • Scenario: composition of Web Services representing actors’ interfaces • BPEL specifications to model the behavior of each participant • long-term process that also contains time-consuming activities • necessity to comply with variety of functional and timing constraints posed by different parties WESC'05

4. Citizen Service Waste Management Office Initial Request Register Protocol Secretary Service Preliminary Notification Evaluate Documents Prepare Integration Procedure Manager Receive Notification Public Notification Receive Notification Collect Integration Provide Integration Technical Committee Invoke TC Start Procedure Technical Analysis Verify Reviews Conference Call Modify Date Final Call Conference Province Board Provide Evaluation Provide Evaluation Receive Acts Send Acts Receive Decision Provide Decision WESC'05

5. Citizen Service Waste Management Office Initial Request Register Protocol Secretary Service Preliminary Notification Evaluate Documents Prepare Integration Procedure Manager Receive Notification Public Notification Receive Notification Collect Integration Provide Integration Technical Committee Invoke TC Start Procedure Technical Analysis Verify Reviews Conference Call Modify Date Final Call Conference Province Board Provide Evaluation Provide Evaluation Receive Acts Send Acts Receive Decision Provide Decision Long activities: manual tasks, decisions,… Timeouts Within 5 days WESC'05

6. Citizen Service Waste Management Office Initial Request Register Protocol Secretary Service Preliminary Notification Evaluate Documents Prepare Integration Procedure Manager Receive Notification Public Notification Receive Notification Collect Integration Provide Integration Technical Committee Invoke TC Start Procedure Technical Analysis Verify Reviews Conference Call Modify Date Final Call Conference Province Board Provide Evaluation Provide Evaluation Receive Acts Send Acts Receive Decision Provide Decision Complex timed requirements: Constraints, regulations, commitments Within 30 days after registration Within 30 days after registration Within 30 days after registration, and at least 10 days before conference At least 5 days before conference Within 90 days after the 1st call WESC'05

7. Timed analysis • Goal Analysis of time-related issues in WS compositions defined by a set of BPEL specifications • Formalize the composition model with explicit representation of time • Represent BPEL timed constructs and activity durations annotations • Represent and analyze complex timed requirements and constraints • Concentrate on “business” time and neglect “technical” time • Solution • Web Service Timed State Transition System (composition behavior) • (subset of) Duration Calculus (complex timed requirements) • Implementation • Discrete time model • Quantified Discrete-time Duration Calculus + DCVALID tool • NuSMV state of the art model checker WESC'05

8. Formal Model • Based on previous work on non-timed analysis of BPEL compositions • Closely related to the formalism of Timed Automata • Each BPEL process is encoded as WS Timed State Transition System • WSTTS (X, S, s0, A, Tr, Inv): • X – set of global clocks (timers) • S – set of states, s0 – initial state • A – set of actions (message input, message output, internal action) • Tr – S x A x Φ x 2X x S – transition relation • Inv – invariants function from S to Φ where φ in Φ has the form true | φ1 AND φ2| x ~ c with ~ in {>, <, =, !=,>=,<=} Action a is fired condition φover timersis true a φ S S’ Y:=0 timers in subset Y are reset WESC'05

9. Formal Model • Based on previous work on non-timed analysis of BPEL compositions • Closely related to the formalism of Timed Automata • Each BPEL process is encoded as WS Timed State Transition System • Semantics of WSTTS network: Global Timed Transitions System Time elapsing transition: • global state is not changed • all timers synchronously increment Internal action of some WSTTS: • internal transition of some WSTTS is executed • timers are not changes Shared communication action of two WSTTS: • two WSTTS execute shared transitions • timers are not changes X’:=X+d X’:=X X’:=X a WESC'05

10. Mapping to WSTTS • Instant activities x ≤ 0 sendCall <invoke name="Customer Call“ operation="sendCall“ partnerLink="CustomerPL"/> x := 0 • Duration annotations x ≤ 0 x ≤ 3 <empty name=“Verify Reviews“ duration=“lessEqual(3D)”/> x ≤ 3 x := 0 • BPEL timeout (for) modifyDate x ≤ 5 <pick> <onMessage operation=“modifyDate”>…</> <onAlarmfor=“PT5D”>…</> x := 0 x = 5 • BPEL timeout (until) modifyDate gt ≤ 12 <pick> <onMessage operation=“modifyDate”>…</> <onAlarmuntil=“12-12-2005”>…</> x := 0 gt = 12 WESC'05

11. Formal Model : Interval Specifications • Duration Calculus • Properties over intervals • Allows to express complex timed requirements of behavioral specifications P P P P P P ¬P D1 D2 D1 D2 D1 x =a x =a+c WESC'05

12. Interval Formula Example Every interval of the behavior that starts with the registration and ends with the conference consists of two subintervals with the call in between, such that the 1st lasts at most 30, and the 2nd at least 10 days. registration call conference len ≤ 30 len ≥ 10 [] ( ([registration]0 ^ true ^ [conference]0) → ( (len ≤ 30) ^ [call]0 ^ (len ≥ 10) ) ) WESC'05

13. Implementation 2. Translate QDDC properties Di into automata A(Di) Timed assumptions (QDDC) 1. Translate annotated BPEL specification into WSTTS composition model M 4. Generate NuSMV specification for the behavioral analysis NuSMV model checker [Annotated] BPEL specifications WSTTS composition model NuSMV Specification Counterexample 5. Verification and counterexample generation Verification properties (LTL,QDDC) 3. Translate (negation of) property P into automaton A(¬P) WESC'05

14. Conclusions • What is done… modelling and analysis of time-related properties of WS compositions • Formal model for the definition of timed behavior of the composition • Mapping of BPEL constructs • Extension with durations annotations for modelling of simple properties • Application of duration calculus for modelling of complex requirements • What is to be done… Translation optimizations and better analysis techniques • State space clustering • math-sat techniques Alternative encoding • UPPAAL model checking Quantitative Analysis • Automated extraction of time bounds from the specifications WESC'05

15. ? Questions WESC'05