1. A Visual Query Language for Business Processes Catriel Beeri Hebrew University Anat Eyal, Simon Kamenkovich, Tel Aviv University Tova Milo

2. Beeri, Eyal, Kamenkovitch, Milo 2006 2 Outline  Introduction and motivation  Overview by example  System and query formal model  Compact representation of query answers  Implementation  Summary

3. Beeri, Eyal, Kamenkovitch, Milo 2006 3 The Standard Example Client PO Service Credit Service Inventory Service Purchase Order Credit Check Reserve Inventory Credit Response Inventory Response Invoice Consolidate Results

4. Beeri, Eyal, Kamenkovitch, Milo 2006 4 Web Services Meet Business Processes Web Service 1 Web Service 2 Web Service 3 Web Service 4 Web Service 5 Web Service n Company A business process Local to company A At company BOn the Web

5. Beeri, Eyal, Kamenkovitch, Milo 2006 5 Recent History of Business Process Standards 2000/05 XLang (Microsoft) 2001/03 BPML (Intallio et al) 2001/05 WSFL (IBM) 2001/06 BPSS (ebXML) 2002/03 BPEL4WS 1.0 (IBM, Microsoft) BPEL4WS 1.1 (OASIS) 2002/062003/01 WS-Choreography (W3C) 2003/04 WSCI (Sun et al) WSCL (HP) 2002/08 BPEL

6. Beeri, Eyal, Kamenkovitch, Milo 2006 6 BPEL in a nutshell Business process -- control and data flow Actions: – atomic –compound : fork, join, while, procedure/process call,… Process spec. represented in XML Commercial products: – design tools with “conceptual” model –Application generators compile to executable code –Application servers execute the code

7. Beeri, Eyal, Kamenkovitch, Milo 2006 7 Points to note Not just a modeling language: applications are automatically generated from the (relatively declarative) specs. There will be plenty of such specs around Specs are data; a lot of interest in querying them: “What kind of credit services are used (in)directly”? “How can I buy a plane ticket ?” “Can one get a price quote without giving first credit card info?”  motivation for developing a query facility

8. Beeri, Eyal, Kamenkovitch, Milo 2006 8 Can a QL be based on BPEL? NO! The BPEL XML representation is machine oriented, unfit for human consumption It decomposes the system diagram into a (XML-based) relational representation of nodes and edges  loss of understanding + queries will require lots of joins Need: Similarity of system and query models

9. Beeri, Eyal, Kamenkovitch, Milo 2006 9 Why not XQuery? (on XML representation of conceptual model) Additional requirements from query language : Graphs rather than trees Queries about control & data flow paths Need to query at different level of granularity –Zoom-in/zoom-out P2P architecture: Specs are distributed  We use a home-brewed QL

10. Beeri, Eyal, Kamenkovitch, Milo 2006 10 Querying Specs, not Runs Not the same semantics –Q: “ does the spec contain these two operations ? ” –V: “ can there be a run that contains these two operations?“ Querying the specs is –Cheaper (specs are data, not possible executions) –Gives a reasonably good approximation for actual runs A (practical) problem with verification: It needs a clear semantics...

11. Beeri, Eyal, Kamenkovitch, Milo 2006 11 Outline  Introduction and motivation  Overview by example  System and query formal model  Compact representation of query answers  Implementation  Summary

12. Beeri, Eyal, Kamenkovitch, Milo 2006 12 A system specification Property, data & activity nodes Control and data flow edges A process is a di-graph of atomic and compound activities Compound activities can be zoomed-in (a-la statecharts)

13. Beeri, Eyal, Kamenkovitch, Milo 2006 13 Travel Agency Process

14. Beeri, Eyal, Kamenkovitch, Milo 2006 14 Zoom In

15. Beeri, Eyal, Kamenkovitch, Milo 2006 15 Queries Use process patterns (like tree patterns for xml) Single/double-headed edges (compare to / and // in XPath) – – edges – – paths of arbitrary length Single/double-bounded activities: –w/o zoom-in –unbounded zoom-in Allow * as node label Node label variables Mark requested nodes/edges by

16. Beeri, Eyal, Kamenkovitch, Milo 2006 16 Query1: provided operations?

17. Beeri, Eyal, Kamenkovitch, Milo 2006 17 Query2: used credit card services? local

18. Beeri, Eyal, Kamenkovitch, Milo 2006 18 Query3: search without login?

19. Beeri, Eyal, Kamenkovitch, Milo 2006 19 Query4: data flow Data elements affected by searchRequest and affecting returnTripResults

20. Beeri, Eyal, Kamenkovitch, Milo 2006 20 Outline  Introduction and motivation  Overview by example  System and query formal model  Compact representation of query answers  Implementation  Summary

21. Beeri, Eyal, Kamenkovitch, Milo 2006 21 Formal Model System: Process graphs + implementation function Graph refinement (graph rewriting) Query: Process patterns + implementation function

22. Beeri, Eyal, Kamenkovitch, Milo 2006 22 System example implementation

23. Beeri, Eyal, Kamenkovitch, Milo 2006 23 Refinement (rewriting) searchTrip refined to

24. Beeri, Eyal, Kamenkovitch, Milo 2006 24 Query Process patterns: * node labels, node variables Nodes / edges can be marked as transitive –Transitive edges: paths of arbitrary length –Transitive node: refinements of arbitrary depth Nodes / edges can be marked as output Patterns related by a query implementation function

25. Beeri, Eyal, Kamenkovitch, Milo 2006 25 Query semantics An embedding: a mapping –from: query graphs (with uniquely identifiable nodes) –to: [refinements of] process graphs satisfying conditions: (nodes): preserves nodes types and labels (edges): edge mapped to edge mapped to a path (imp): preserves implementation relationships A result: image of query graph under an embedding Answer: all results

26. Beeri, Eyal, Kamenkovitch, Milo 2006 26 Examples: A B C A1 B2 B3 *4 A1 B2 B3 C4 answersystemquery

27. Beeri, Eyal, Kamenkovitch, Milo 2006 27 Examples: A B C A1 B2 B3 *4 A1 B2 B3 C4 Answer: System: Query A B C D A1 B2 D3 A1 B2 C B D3

28. Beeri, Eyal, Kamenkovitch, Milo 2006 28 Outline  Introduction and motivation  Overview by example  System and query formal model  Compact representation of query answers  Implementation  Summary

29. Beeri, Eyal, Kamenkovitch, Milo 2006 29 Many fork/joins  exponential number of paths Large or Infinite answers!

30. Beeri, Eyal, Kamenkovitch, Milo 2006 30 Infinite answers can be generated by either Cycles in process graph (example seen previously) Cycles (recursion) in zoom-in relationships  Infinite # of refinements Path vars (double headed edges) + cycles  infinite # of results

31. Beeri, Eyal, Kamenkovitch, Milo 2006 31 Recursive zoom-in

32. Beeri, Eyal, Kamenkovitch, Milo 2006 32 A query with an infinite answer

33. Beeri, Eyal, Kamenkovitch, Milo 2006 33 Finite representation

34. Beeri, Eyal, Kamenkovitch, Milo 2006 34 Systems and queries are essentially regular graph grammars Bad news:  not closed under intersection (general case) Good news: –Our systems and queries are sufficiently simple: Psize representation (as a regular grammar) can be computed in Ptime (data complexity!) skip

35. Beeri, Eyal, Kamenkovitch, Milo 2006 35 Answer construction Observations: Embeddings (results) can be composed of query pattern to system process embeddings (results) glue: the constraint (imp) Multiple embeddings can be represented by a shared node mapping (that satisfies (nodes) and (edges) -- a homomorphism)  Construction of node mappings is the core problem

36. Beeri, Eyal, Kamenkovitch, Milo 2006 36 Node mapping/answer construction The simple case: from p Q to p S (not into refinement) : Find node mappings that satisfy (nodes), (edges): NP-complete in p Q (query), Ptime in p S (data) Results are 1-1 images of mappings: – each query node is distinct, – new nodes and edges for paths (images of ) A B C D A1 B2 D3 A1 B2 C B D3

37. Beeri, Eyal, Kamenkovitch, Milo 2006 37 The complex case: from p Q to refinement of p S : A mapping may be split into parts: –into p S itself –into implementation of a compound action of p S, and so on with double-headed edges – to any depth, including cycles Observations: Only sub-graphs of p Q with single entry/exit can be mapped to an implementation In one mapping, a disjoint set of such graphs can be mapped to an implementation

38. Beeri, Eyal, Kamenkovitch, Milo 2006 38 The construction: For each p Q and p S : For disjoint set J of such sub-graphs, construct mappings for p Q /J (each member of J replaced by $* node) to p S Do same for also for these sub-graphs Glue together using by a regular grammar: –$* nodes (suitably labeled) are non-terminals –Each node (for G) is associated with the mappings for G

39. Beeri, Eyal, Kamenkovitch, Milo 2006 39 C Query : A B B F D E C A B System : A C

40. Beeri, Eyal, Kamenkovitch, Milo 2006 40 Extensions to QL: OK extensions: –label predicates, –Regular path expressions (on node labels), –Negation, –Joins on node labels Not OK extensions : –Joins on path variables The result is not a regular graph grammar Emptiness is undecidable NP-hard even without cycles and recursion

41. Beeri, Eyal, Kamenkovitch, Milo 2006 41 Outline  Introduction and motivation  Overview by example  System and query formal model  Compact representation of query answers  Implementation  Summary

42. Beeri, Eyal, Kamenkovitch, Milo 2006 42 Simple and intuitive query formulation similar to how processes are specified Operates in distributed environment System and queries modeled as graph grammars  allows compact representation of large/infinite answers Ignores semantics of composite actions AXML as an implementation platform supports –Transparent distribution –Taking advantage of built-in optimizations

43. Beeri, Eyal, Kamenkovitch, Milo 2006 43 High Lights of Model & QL Base system unit: directed node-labeled graph QL primitives|: /, // (forward axis only) Node equality Node label equality Node label predicates Regular expressions on node labels in paths Negation on sub-patterns Can be seen as adaptation of XPath to di-graphs, but selection not restricted to one path

44. Beeri, Eyal, Kamenkovitch, Milo 2006 44 Advanced system structure: an infinite family of directed node-labeled graphs, specified by a graph grammar Additional QL primitives: double-headed node: query on all graphs derived from a given graph Answer representation as a graph grammar

45. Beeri, Eyal, Kamenkovitch, Milo 2006 45 Future work Investigate queries on logs Does this pattern exist? “Querying of runs” – essentially verification “Marxist” extensions to QL primitives