Financial. Analysis. O.Eval = {Low, High} Store. Bid. Update. Risk. Technical. Evaluation. External Consultant

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1 ACM PODS98 of CS Dept at Stony Brook University Based Modeling and Analysis of Logic Workows Hasan Davulcu* N.Y , U.S.A. * Joint with M. Kifer, C.R. Ramakrishnan, I.V. Ramakrishnan Hasan Davulcu { University at Stony Brook 1

2 A collection of inter-related tasks and transactions Workow: to carry out a well-dened business process. designed Management: Automated coordination of work, Workow processing entities, to achieve an overall business goal. among Management System (WfMS): System for Workow of workow processes (like DBMS facilitates automation Workows creation and maintenance of large data sets). Hasan Davulcu { University at Stony Brook 2

3 What Kind of Computations are Workows? Long-running: Hours, days, months; Autonomous, distributed processing entities; Transactional Semantics. Hasan Davulcu { University at Stony Brook 3

4 Control Flow Graph: Bid Evaluation Example Contractor Evaluation o O.Eval = {Low, High} Financial Analysis f Receive Bid r AND c Cost Update C.Cost < Budget b Budget Update s Store Bid d Final Decision D.Final = Accept XOR D.Final = Reject OR t e Technical Evaluation External Consultant i m Risk Analysis Consultant Billing Global Coordination Dependencies: 1. IF o.eval = low THEN not e 2. IF occurs (e) THEN o before e 3. IF occurs (t) AND occurs (e) THEN e before i 4. c before f Hasan Davulcu { University at Stony Brook 4

5 Coordination: How to schedule tasks automatically? Central Workow Problems a XOR b c d 1. d before c 2. b AND IF occurs (b) THEN c Is control ow graph and coordination dependencies Consistency:? consistent Does the specication satisfy certain key properties? Correctness: Every bid is either accepted or rejected by the bid-evaluation e.g., workow. Hasan Davulcu { University at Stony Brook 5

6 A formal language to specify the structure of processes Creation: their interactions at a high-level; and Reasoning methods to ascertain that a workow is Verication: correct; Techniques for automatically deriving correct Execution: from high-level specications. executions What is Needed to Enable Workow Automation? Ideally, all should t in a single, unifying framework. Hasan Davulcu { University at Stony Brook 6

7 { Sequential and concurrent composition; { Subroutines (e.g. sub-workows); { Declarative queries (e.g. transition conditions); { Atomicity; { Isolation; Requirements for Workow Specication Primitives for modular specication Temporal constraints for expressing coordination dependencies. Triggers (e.g. exceptions) Hasan Davulcu { University at Stony Brook 7

8 { Suitable for specifying reactive behavior. [Dayal et.al.-91,96] Related Research on Workows Extended Transaction Models Permits hierarchical structures and relaxes ACID properties. { [Elmagarmid-90] Task Dependencies Declarative constructs suitable for specifying global coordination { [Klein-91, Singh-96] dependencies. Active Rules and Triggers Petri Nets and Temporal Logics Suitable for modeling and verifying concurrent processes. { et.al.-93, Nabil et.al.-98] [Sheth Hasan Davulcu { University at Stony Brook 8

9 { Declarative queries { Concurrent updates { Transactional behavior Model Theory: { A model assigns transaction formulas truth values over paths. Informally, being true over path means \ can execute along." Constructs execution paths as it proves statements. Our Framework: Concurrent Transaction Logic (CT R ) CT R : Conservative extension of rst order logic for programming, executing and reasoning with state-changing concurrent processes. CT R uniformly models: (i.e., nite sequences of states) Proof Theory: { Sound and complete. Hasan Davulcu { University at Stony Brook 9

10 CT R : Logical Connectives cost update budget update means, \Execute cost update and then budget update". execute D D D D D D D D cost_update budget_update (contractor nancial) j (consultant billing) means, \Execute f inancial) and (consultant billing) in an interleaved (contractor fashion". D D D D D D D D contractor consultant financial billing ( contractor financial ) ( consultant billing ) Hasan Davulcu { University at Stony Brook 10

11 db updates means, \Execute db updates in isolation". CT R : Logical Connectives bid eval ^ c before f means, \Execute bid eval and c bef ore f along the path". (i.e. ^ can be used to express constraints on execution.) same c_before_f D D D D D D D D bid_eval internal eval _ external contractor means, \Execute either internal eval external contractor". or : external contractor means, \Do anything but an execution of contractor". external db updates cost update budget update means, \An execution of update budget update is also an execution of db updates". cost ( is dened as _:). Hasan Davulcu { University at Stony Brook 11

12 Control-ow graphs translates straightforwardly into CTR formulas: Putting It Altogether : Bid-Evaluation Workow bid eval r (f inancial j db updates j technical) rest f inancial o ([o:eval = \high"] f ) _ (low f ) db updates (c [c:cost < budget] b) s technical (t i) _ (e m) _ (t i j e m) Global Coordination Dependencies can be modeled as conjunction of set of dependencies C. a 1: Olow! :Oe 3: Ot ^ Oe! Oe Oi 2: Oe! (Oo Oe) 4: Oc Of ( O means \ occurs sometime".) Workow specication: bid eval ^ C Hasan Davulcu { University at Stony Brook 12

13 Constraints are CT R formulas. Temporal Dependencies 1. Existence constraints: Oe, :Oe (e must/must not occur); 2. Serial constraints: Oe Of (e must occur before f); 3. Complex constraints: C 1 ^ C 2, and C 1 _ C 2, if C 1, C 2 are constraints.. Hasan Davulcu { University at Stony Brook 13

14 Executing a workow G ^ C by the general proof theory has run-time complexity. exponential We develop a re-write system, Apply, which transforms G ^ C an equivalent ^-free formula G C such that: into { Execution and verication becomes more ecient on G C. Transformation Apply Hasan Davulcu { University at Stony Brook 14

15 Workow Analysis with CT R : G C if satisable and G C is ^-free A legal execution of C ^ G can be picked from G C { Inconsistency: I Apply (C, bid eval) false { Verication: Given a property : Proposition (Apply): 8 < Apply (C; G) C ^ G false if C ^ G is unsatisable in linear time by the inference system. 2 8 < Apply (:; G C ) false if holds for G C G : all counter executions of C^: Inconsistency and verication reduce to the same logical problem { unsatisability. Hasan Davulcu { University at Stony Brook 15

16 Apply Transformation: Contd. α γ XOR β δ η Example: If T is ( ), then Apply (O; T ) = O ^ T = Apply (:O; T ) = :O ^ T = ( _ ) Hasan Davulcu { University at Stony Brook 16

17 = ( send()) j (receive() ) j 1 j ::: j n Apply Transformation: Contd. AND γ XOR β ρ ρ 1 n α XOR δ Example: Apply ( O O; ( _ ) j ( _ ) j 1 j ::: j n ) Hasan Davulcu { University at Stony Brook 17

18 Knot Detection and Elimination Insertion of send/receive may cause a cyclic wait, which we call a knot. Wf Coord. Dependencies : Receive Bid 1. I before O OR 2. If occurs (E) then O before E 3. If occurs (T) AND occurs(e) then E before I R AND Technical Evaluation T Contractor Evaluation O 2 E I 1 3 External Consultant Risk Analysis D Final Decision Excise Transformation rewrites the above workow into a knot-free Receive Bid R AND Technical Evaluation XOR Contractor Evaluation O T I Risk Analysis D Final Decision E External Consultant workow: Hasan Davulcu { University at Stony Brook 18

19 (Consistency) Theorem workow specication G ^C is inconsistent i Excise(Apply (C; G)) false. A (Correctness) Theorem is a constructive way of verifying workow properties with Apply. There (Coordination) Theorem jgj denote the size of a control-ow graph, then we can pick a legal Let (Complexity) Let jgj denote the size of a control-ow graph, N be the Theorem of constraints in C, and d be the largest number of disjuncts in a constraint. number Results execution from Excise(Apply (C; G)) in time linear in jgj. The worst-case size of Apply (C; G) is O(d N jgj). (where as standard model-checking algorithms for this problem are exponential in jgj) For certain classes of constraints Apply (C; G) is linear in jgj. Excise(G) is linear in jgj. Hasan Davulcu { University at Stony Brook 19

20 Data Value Dependencies: Include transition conditions in analysis; Future Work Management: Facilitate failure detection and handling with Failure features like contingency and compensation; advanced Management: Improve support for triggers to facilitate Exception behavior due to exceptions; reactive Workows with Loops. Hasan Davulcu { University at Stony Brook 20