Published on December 8, 2008
Semantics (requirements) of Business Process Ang Chen 31 Jan. 2008
Objective: to observe • The requirements of BP semantics via Workﬂow Patterns and BPEL • The role of Petri Net in BP modeling: Graphical notation? Semantics foundation? Executable language? • Advantages / disadvantages of using PN as semantics basis of BP (e.g. comparing with Pi-calculus) • The missing part of BP modeling with PN, i.e. the data-ﬂow A.Chen, 31 jan 2008 2
Papers • . Workﬂow Patterns. W.M.P van der Aalst, A.H.M. ter Hofstede, B. Kiepuszewski, and A.P. Barros. Distributed and Parallel Databases, 14(3), July 2003 • . Formal semantics and analysis of control ﬂow in WS-BPEL. Science of Computer Programming,Volume 67, Issues 2-3, 1 July 2007. Chun Ouyang, Eric Verbeek, Wil M.P. van der Aalst, Stephan Breutel, Marlon Dumas and Arthur H.M. ter Hofstede • . A pi-calculus based semantics for WS-BPEL. Journal of Logic and Algebraic Programming,Volume 70, Issue 1, January 2007. Roberto Lucchi and Manuel Mazzara • . Information System Behavior Speciﬁcation by High-Level Petri Nets. A. Oberweis, P. Sander. ACM Transactions on Information Systems,Vol. 1, No. 4, October 1996 • . Petri Net + Nested Relational Calculus = Dataﬂow. Jan Hidders, Natalia Kwasnikowska, Jacek Sroka, Jerzy Tyszkiewicz, and Jan Van den Bussche. 2005 A.Chen, 31 jan 2008 3
Topics • Workﬂow Patterns  and BPEL: they represent requirements of business process modeling in academic and industry, respectively • Semantics (of BPEL control-ﬂow): Petri Net , Pi-Calculus  • Data-Flow modeling:   • Not included: Transaction A.Chen, 31 jan 2008 4
Topics  Workﬂow realize Petri Net patterns formalization  use   BPEL Data-Flow Modeling formalization  Pi-Calculus A.Chen, 31 jan 2008 5
Outline • Non-local semantics of workﬂow patterns • BPEL formalization • Data-Flow Modeling in BP • Conclusion A.Chen, 31 jan 2008 6
Non-local semantics of Workﬂow Patterns
Workﬂow patterns • . identiﬁes 20 control-ﬂow patterns and uses them to evaluate products • Basic constructs (1-5): sequence, join, split • Advanced branching and synchronization (6-9): merges • Structural (10-11): arbitrary cycle, implicit termination • Multi-instances (12-15) • State-Based (16-18) • Cancellation (19-20) A.Chen, 31 jan 2008 8
Non-local semantics (Join) I A D split B join C E • Non-blocking (asynchronous) Join (N of M): select N from M without waiting M inputs •xor-join:1 of M non-blocking join, D or E are activated once per case •multi-merge: D, E can be activated several times per case •discriminator: D, E can be activated several times, then reset A.Chen, 31 jan 2008 9
Non-local semantics (Join) II B E A split join G C F • In non-blocking join, the connector needs non-local information to take decision A.Chen, 31 jan 2008 10
Non-local semantics of workﬂow patterns • Most workﬂow patterns need non-local information between the activities, e.g. merge, case cancellation, cycles with multiple instances ... A.Chen, 31 jan 2008 11
Role of PN • PN can be a semantics basis • pros: easy to be veriﬁed for analysis purpose • cons: few patterns can be modeled directly due to its local semantics • Not easy to directly model BP with PN, extension of PN semantics is necessary A.Chen, 31 jan 2008 12
BPEL • Business Process Execution Language based on Web Service, for the composition of Web Service • Units of composition: Activity, Scope • Control-Flow constructs: sequence, ﬂow, switch, pick, while, link, fault, compensation • The speciﬁcation does not provide a formal semantics, thus not clear (or ambiguous) in some details, e.g. completion conditions of parallel tasks A.Chen, 31 jan 2008 14
BPEL Semantics • Semantics of BPEL control-ﬂow in Petri Net  and Pi-Calculus  • Both: obtain unambiguous semantics of BPEL •  provides static analysis methods, e.g. ﬁnd unreachable activities •  possible to verify the behavioral equivalence of processes (future work) A.Chen, 31 jan 2008 15
Petri Net  to skip Y Ready to skip Y Ready Start Y Start skip Y X skip Run X X Run X C Y Y Completed X skipped Y Completed skipped Finished Activity X Y ! :-) Finished Scope Q • Activities and scopes are transformed into PN structure • State-oriented, easy to ﬁnd case states A.Chen, 31 jan 2008 16
Pi-Calculus  • Formalization of control-ﬂow is quite direct, but difﬁcult to read • Abstraction of service is well preserved, e.g. action signature • Channels are used to handle faults and compensations • States of processes are encoded, however, states of cases are lost A.Chen, 31 jan 2008 17
BPEL formalization • There has been debates on the semantics basis of BP languages, e.g. PN vs. Pi-calculus • Each approach has its advantages • Till now, veriﬁcations are limited to static control-ﬂow analysis • Data-ﬂow analysis is missing A.Chen, 31 jan 2008 18
Data-Flow Modeling in BP
Data-Flow • Very general topic, many work have been done in database and parallel computing domain • Few publications in BP modeling, especially the integration of Control-Flow and Data-Flow (e.g. be able to extract CF from DF) •  ,  try to address the data-ﬂow problem in information system with Petri Net (control-ﬂow + data-ﬂow) A.Chen, 31 jan 2008 20
Data-Flow modeling  •  proposes Predicate/Transition Net + Nested Relation Calculus • Add formally deﬁned behaviors to information systems • Processes are modeled by Predicate/Transition Net, tokens are relation instances • A different approach than CRUD in SQL to manage data (based on insertion and deletion of tuples) A.Chen, 31 jan 2008 21
NR/T Net • Places are relations, relation instances are sets of tuples • Use tuples and ﬁlter table to manipulate relation instances • Filter tables inscribed on PN arcs give rules of manipulating instances (Inclusion order vs. Object order) • Transitions are annotated by logical formulas A.Chen, 31 jan 2008 22
Data-Flow modeling  •  : Petri Net + Nested Relational Calculus = Data-Flow Language • Use operations on set and record • Edge annotation (simple condition), transition label (set operations, user-deﬁned labels) • Use simple control-ﬂow, it is designed to describe the ﬂow of large amount of data • CRUD operations on data are not concerned A.Chen, 31 jan 2008 23
Data-Flow • Control-ﬂow is a particular kind of data- ﬂow • No convenient solutions (yet) for data-ﬂow modeling in BP • Related topic: process mining tries to discover control-ﬂow from observed data- ﬂow A.Chen, 31 jan 2008 24
Conclusion • This study motivates to propose an approach which: • Integrates Control-Flow and Data-Flow • Supports relational data model • Based on PN or Process algebra, or both • Can be a semantics basis of BPEL and other languages • Supports all workﬂow patterns, if possible A.Chen, 31 jan 2008 25
BP Modeling with ID- Net • Places are typed, e.g. by relations. Tokens are identiﬁcations, e.g. relation keys • Transitions are processes whose behaviors are described by process algebra • Operations on relational data are attached to the transition process without changing the ID-Net’s control-ﬂow, i.e. data-ﬂow integration • Both case state and process state are traceable A.Chen, 31 jan 2008 26
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