1. Reasoning about the Behavior of Semantic Web Services with Concurrent Transaction Logic Presented By Dumitru Roman, Michael Kifer University of Innsbruk, State University of New York 2008-01-04 Summerized By Sungchan Park

2. Copyright  2008 by CEBT Overview  Improve the authors’ previous works on Web Service modeling Concurrent Transaction Logic(CTR) – Logic based Modeling and Analysis of Workflows. 1998 – A Logical Framework for Scheduling Workflows under Resource Allocation Constraints. 2002 – CTR-S: A Logic for Specifying Contracts in Semantic Web Services. 2004 Reasoning about behavior about WS – Contracting, Enactment Improvement – Conditional control, data flow – More general constraints – Simpler logic than CTR-S Center for E-Business Technology

3. Copyright  2008 by CEBT Modeling & Reasoning about Service Behavior Center for E-Business Technology

4. Copyright  2008 by CEBT Modeling & Reasoning about Service Behavior: Example Center for E-Business Technology

5. Copyright  2008 by CEBT The Basics of CTR  Atomic formula P(t 1, t 2, …, t n ) – P : predicate – t i : function term Complex formulas are built using connectives and quantifiers  Informal Sematics Database states – Eg. s 1, s 2, …, s n Paths( sequences of states) – Eg.,, … – Truth value of CTR formula is determined over path – Formula a is true over a path iff a can “excute” starting at state s 1, change to s 2, s 3, … etc. Will terminate at state s n. Center for E-Business Technology

6. Copyright  2008 by CEBT The Basics of CTR, Cont.  CTR Connectives a ⊗ b – execute athen execute b a | b – a and bmust both execute concurrently in an interleaved fashion. a b – a and b must both execute along the same path – Constraints a b – execute a or execute b non-deterministically ¬a – execute in any way, provided that this will not be a valid execution of a ⊙ a – execute a in isolation execution i.e., without interleaving with other concurrently running activities Center for E-Business Technology

7. Copyright  2008 by CEBT Concurrent-Horn subset of CTR  Concurrent-Horn rule p ← q – Means “if q can execute along path, then so p can do” – p : atomic formula – q : concurrent horn goal Atomic formula a ⊗ b, a | b, a V b when a and b are concurrent horn goals ⊙ a when a is concurrent horn goal Examples – Process ← a ⊗ ( b | Subproc ) ⊗ g – Subproc ← ( c ⊗ ( d v ( e ⊗ f ))) Center for E-Business Technology

8. Copyright  2008 by CEBT Concurrent-Horn subset of CTR, Cont.  Can use SLD-like proof procedure In previous work, G C can be transformed into horn goal by limiting class of constraints  In present work, however, the extended proof theory of CTR overcomes the limitation of constraints Center for E-Business Technology

9. Copyright  2008 by CEBT Modeling Services with CTR: Control Flow Center for E-Business Technology

10. Copyright  2008 by CEBT Modeling Services with CTR: Constraints  Unlike previous works, we use predicates with variables—not just propositions—to represent control and data flow.  Constraints Algebra Event – e = ∃ DataFlowVar eventName(DataFlowVar) Primitive – ∇ e : Event e must happen = path ⊗ e ⊗ path – ¬ ∇ e : Event e must not happen Immediate serial constraints – ∇ ⊙ (e 1 ⊗ … ⊗ e n ) : e 1, …, e n happen next to each other with no other event in- between Serial constraints – ∇ (e 1 ⊗ … ⊗ e n ) : e 1, …, e n excute in that order with possible interleaving Complex constraints – C 1 ∧ C 2, C 1 ∨ C 2 Center for E-Business Technology

11. Copyright  2008 by CEBT Modeling Services with CTR: Constraints, Cont.  Expression Examples Events e and f must both occur (in any order) – ∇ e ∧ ∇ f It is not possible for e and f to happen together – ¬ ∇ e ∧ ¬ ∇ f If event e occurs, then f must also occur (before or after e) – ∇ e → ∇ f If event e occurs, then f must occur later – ∇ e → ( ∇ e ⊗ ∇ f) If event f has occurred, then event e must have occurred some time prior to that – ∇ f → ( ∇ e ⊗ ∇ f) If both e and f occur, then e must come before f – ( ∇ e ∧ ∇ f) → ( ∇ e ⊗ ∇ f) If event e occurs, then f must occur right after e with no event in-between – ∇ e → ∇ ⊙ (e ⊗ f) If k and d both occur then d must happen right after k with no other event in-between – ( ∇ k ∧ ∇ d) → ∇ ⊙ (k ⊗ d) Center for E-Business Technology

12. Copyright  2008 by CEBT Modeling Services with CTR: Constraints, Cont. Center for E-Business Technology

13. Copyright  2008 by CEBT Modeling Services with CTR: Data Flow and Conditional Control Flow  Data flows imply constraints Center for E-Business Technology

14. Copyright  2008 by CEBT Modeling Services with CTR: Data Flow and Conditional Control Flow  Conditions in control flow are checked ahead and unsatisfiable branches are eliminated Center for E-Business Technology

15. Copyright  2008 by CEBT Reasoning about Choreography and Contracts  Contracting Determine if contracting for the service is possible – Find out if there is an execution of the CTR formula G ∧ C given the set of service choreography definition R – Check that there is a path s 1, s 2, …, such that R, s 1, …, s k ㅑ G ∧ C  Enactment Find a constructive proof that – R, s 1, …, s k ㅑ G ∧ C for some paht s 1, …, s k – Each proof is a way to execute the choreography so that all constraints are satisfied Center for E-Business Technology

16. Copyright  2008 by CEBT Reasoning about Choreography and Contracts, Cont.  Phase 1 Transform to normal form – From G ∧ C to ∨ i (G i ∧ j serialConstr ij ) Gi is a concurrent-Horn goal and SerialConstrij is either an immediate serial constr. or a serial constr. – NP-Complete in the size of largest number of disjuncts in C  Phase 2 Find the proof using inference rules – If proof is found, them enactment of the service is possible – Linear in the size of the execution path Center for E-Business Technology

17. Copyright  2008 by CEBT Reasoning about Choreography and Contracts, Phase 1  Transformation rules Applying Complex Constraints Applying Primitive Constraints If the result is ¬path, then enactment is not possible Otherwise, the result is a formula of the form ∨ i(Gi ∧ j serialConstrij) Center for E-Business Technology

18. Copyright  2008 by CEBT Reasoning about Choreography and Contracts, Phase 2  Phase 2 has two step 1.Check constraints for internal consistency and eliminate redundancy 2.Apply inference rules Center for E-Business Technology

19. Copyright  2008 by CEBT Reasoning about Choreography and Contracts, Phase 2:Step 1  Check inconsistency Inconsistent patterns  Eliminate redundancy Examples Center for E-Business Technology

20. Copyright  2008 by CEBT Reasoning about Choreography and Contracts, Phase 2:Step 2  Extended Inference System hot( Ψ ) – “ready to be excute” 1.hot( Ψ ) = Ψ, if Ψ is atomic formula 2.hot( Ψ ⊗ Ф ) = hot( Ψ ) 3.hot( Ψ | Ф ) = hot( Ψ ) | hot( Ф ) 4.hot( Ψ ∨ Ф ) = hot( Ψ ) ∨ hot( Ф ) enabled(C) – The set of enabled component of a set of constraints C is as follows: enabled(C) = {x | x is a root node of C or x is not in C} eligible( Ψ ) – x, if x ∈ hot( Ψ ) ∩ enabled(C) and x is and exclusive node in C – hot( Ψ ) enabled(C), otherwise eligible( Ψ ) ⊆ hot( Ψ ) Center for E-Business Technology

21. Copyright  2008 by CEBT Reasoning about Choreography and Contracts, Phase 2:Step 2, Cont.  Inference rules 1.Applying transactional definitions – If b ← β be a rule in P and assume that its variables have been renamed so that none are shared with Ψ. If a and b unify with the most general unifier σ then then, – Ψ’ is Ψ with some occurrence replaced with b – C’ is C after deleting a and splicing edges adjacent on a 2.Querying the database – If ( ∃ )a σ is true in D and a σ and G’ σ share no var. then, – Ψ’ is Ψ with some occurrence of a deleted Center for E-Business Technology

22. Copyright  2008 by CEBT Reasoning about Choreography and Contracts, Phase 2:Step 2, Cont.  Inference rules, cont. 3.Executing elementary updates – If a σ is an elementary state transition from state D1 to D2 then – Ψ’ is Ψ with some occurrence of a deleted – C’ is C with after deleting some nodes 4.Executing atomic transactions – If ⊙ α is hot component in then, – Ψ’ is Ψ with some occurrence of a deleted Center for E-Business Technology

23. Copyright  2008 by CEBT Reasoning about Choreography and Contracts, Phase 2:Step 2, Cont.  Difference with previous CTR inference system 1.Rule 3 operates on eligible occurrence of atomic formula, while previous one did on a larger set of hot occurrence 2.Rule 1 and 3 also modify the set of constraints Center for E-Business Technology

24. Copyright  2008 by CEBT Bird’s Eye View of the Approach  The Web service designer starts to build Web service choreography by drawing a control flow graph, a data flow graph, and specifying service policy using a GUI tool. The logical representations can be constructed automatically from an appropriately instrumented GUI tool.  The designer then uses the algorithm to find un-enactable parts of the control flow graph.  The designer uses the CTR reasoner-based algorithm to make sure that the control graph is consistent with the service policies.  The client submits the contract requirements to verify that a contract is possible. As before, verification is done using the CTR. Center for E-Business Technology

25. Copyright  2008 by CEBT Related Work  Service contracting Existing work focuses on defining frameworks, models, and architectures different aspects and phases of e-contracting (negotiation, enforcement, violation detection, monitoring, legal aspects) We provide a simple yet realistic and useful framework for e-contracting – Solve a concrete problem in establishing of contracts and enacting Web services  Workflow/process modeling Many languages for process modeling, e.g. YAWL, DecSerFlow Ours is as expressive as DecSerFlow, and additionally integrates with conditional control flows, data flows, provides reasoning mechanisms  Process verification Most of the existing approaches use model checking for verification – Complexity exponential in the size of the control graph CTR’s integrates several process modeling paradigms: conditional control flows, data flows, hierarchical modeling, constraints – Complexity polynomial in the size of the control graph and exponential in the size of the constraints (due to better structuring of the problem) Center for E-Business Technology

26. Copyright  2008 by CEBT Conclusion  Formulated the problems of choreography, contracting, and enactment for semantic Web services using Concurrent Transaction Logic complex set of constraints data flow and conditional process controls extended CTR proof theory  Presented reasoning techniques for deciding if automatic contracting for a service is possible finding a choreography that obeys the policy of the service and the user requirements of the contract enacting the service  Can be extended to multi-party contracts  Possible extensions more expressive interaction patterns, e.g. loops subsets of constraints for which the verification problem has a better complexity Center for E-Business Technology