A Visual Query Language for Business Processes Catriel Beeri Hebrew University Anat Eyal, Simon Kamenkovich, Tova Milo Tel Aviv University Beeri, Eyal, Kamenkovitch, Milo 2006
Outline v Introduction and motivation v Overview by example v System and query formal model v Compact representation of query answers v Implementation v Summary Beeri, Eyal, Kamenkovitch, Milo 2006 2
The Standard Example itt edi red nse C c Cr eo k p h Cs Re Purchase Invoice Order Client Credit Service Consolidate Results PO Service In. R ve RIn ento es serry ve po ve nto ns ey r Inventory Service Beeri, Eyal, Kamenkovitch, Milo 2006 3
Web Services Meet Business Processes Local to company A Web Service 1 Web Service 4 Web Service 2 Web Service 5 Web Service 3 Web Service n At company B On the Web Company A business process Beeri, Eyal, Kamenkovitch, Milo 2006 4
Recent History of Business Process Standards BPML BPSS WSCI WS-Choreography (Intallio et al) (eb. XML) (Sun et al) (W 3 C) 2000/05 2001/03 2001/05 2001/06 2002/03 2002/06 2002/08 2003/01 2003/04 XLang WSFL WSCL BPEL 4 WS 1. 0 BPEL 4 WS 1. 1 (Microsoft) (IBM) (HP) (IBM, Microsoft) (OASIS) BPEL Beeri, Eyal, Kamenkovitch, Milo 2006 5
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 Beeri, Eyal, Kamenkovitch, Milo 2006 6
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 Beeri, Eyal, Kamenkovitch, Milo 2006 7
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 Beeri, Eyal, Kamenkovitch, Milo 2006 8
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 • P 2 P architecture: Specs are distributed We use a home-brewed QL Beeri, Eyal, Kamenkovitch, Milo 2006 9
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. . . Beeri, Eyal, Kamenkovitch, Milo 2006 10
Outline v Introduction and motivation v Overview by example v System and query formal model v Compact representation of query answers v Implementation v Summary Beeri, Eyal, Kamenkovitch, Milo 2006 11
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) Beeri, Eyal, Kamenkovitch, Milo 2006 12
Travel Agency Process Beeri, Eyal, Kamenkovitch, Milo 2006 13
Zoom In Beeri, Eyal, Kamenkovitch, Milo 2006 14
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 ü Beeri, Eyal, Kamenkovitch, Milo 2006 15
Query 1: provided operations? Beeri, Eyal, Kamenkovitch, Milo 2006 16
Query 2: used credit card services? local Beeri, Eyal, Kamenkovitch, Milo 2006 17
Query 3: search without login? Beeri, Eyal, Kamenkovitch, Milo 2006 18
Query 4: data flow Data elements affected by search. Request and affecting return. Trip. Results Beeri, Eyal, Kamenkovitch, Milo 2006 19
Outline v Introduction and motivation v Overview by example v System and query formal model v Compact representation of query answers v Implementation v Summary Beeri, Eyal, Kamenkovitch, Milo 2006 20
Formal Model System: • Process graphs + implementation function • Graph refinement (graph rewriting) Query: Process patterns + implementation function Beeri, Eyal, Kamenkovitch, Milo 2006 21
System example implementation Beeri, Eyal, Kamenkovitch, Milo 2006 22
Refinement (rewriting) search. Trip refined to Beeri, Eyal, Kamenkovitch, Milo 2006 23
Query Process patterns: • * node labels, node variables • Nodes / edges can be marked as transitive – Transitive edges: – Transitive node: paths of arbitrary length refinements of arbitrary depth • Nodes / edges can be marked as output Patterns related by a query implementation function Beeri, Eyal, Kamenkovitch, Milo 2006 24
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 a path (imp): preserves implementation relationships • A result: image of query graph under an embedding • Answer: all results Beeri, Eyal, Kamenkovitch, Milo 2006 25
Examples: system A B answer A 1 *4 C A 1 C 4 query B 2 B 3 Beeri, Eyal, Kamenkovitch, Milo 2006 26
Examples: System: A B A D C B C Query A 1 *4 B 2 B 3 A 1 B 2 D 3 Answer: A 1 C 4 B 2 B 3 A 1 D 3 B 2 Beeri, Eyal, Kamenkovitch, Milo 2006 C B 27
Outline v Introduction and motivation v Overview by example v System and query formal model v Compact representation of query answers v Implementation v Summary Beeri, Eyal, Kamenkovitch, Milo 2006 28
Large or Infinite answers! Many fork/joins exponential number of paths ü ü Beeri, Eyal, Kamenkovitch, Milo 2006 29
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 Beeri, Eyal, Kamenkovitch, Milo 2006 30
Recursive zoom-in Beeri, Eyal, Kamenkovitch, Milo 2006 31
A query with an infinite answer Beeri, Eyal, Kamenkovitch, Milo 2006 32
Finite representation Beeri, Eyal, Kamenkovitch, Milo 2006 33
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 Beeri, Eyal, Kamenkovitch, Milo 2006 34
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 Beeri, Eyal, Kamenkovitch, Milo 2006 35
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 D A 1 B ) C B 2 D 3 A 1 D 3 B 2 Beeri, Eyal, Kamenkovitch, Milo 2006 C B 36
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 Beeri, Eyal, Kamenkovitch, Milo 2006 37
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 Beeri, Eyal, Kamenkovitch, Milo 2006 38
Query : A System : A D B B E C C F Beeri, Eyal, Kamenkovitch, Milo 2006 39
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 Beeri, Eyal, Kamenkovitch, Milo 2006 40
Outline v Introduction and motivation v Overview by example v System and query formal model v Compact representation of query answers v Implementation v Summary Beeri, Eyal, Kamenkovitch, Milo 2006 41
• 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 Beeri, Eyal, Kamenkovitch, Milo 2006 42
High Lights of Model & QL Base system unit: directed node-labeled graph QL primitives|: • /, // (forward axis only) • Node 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 Beeri, Eyal, Kamenkovitch, Milo 2006 43
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 Beeri, Eyal, Kamenkovitch, Milo 2006 44
Future work • Investigate queries on logs Does this pattern exist? • “Querying of runs” – essentially verification • “Marxist” extensions to QL primitives Beeri, Eyal, Kamenkovitch, Milo 2006 45
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