2008/10E-Enterprise Integration - eEI1 Lecture 6 Petri Net Techniques for Modeling Workflows and Their Support of Reuse

E-Enterprise Integration - eEI2 Abstract 4 Several authors propose their own technique based on Petri Nets to model workflow processes. But suggest totally different solutions. 4 Because the proposed techniques and fundamentally different, eleven of these techniques are briefly discussed and compared

E-Enterprise Integration - eEI3 What is workflow? 4 The automation of a business process, in whole or part, during which documents, information or tasks are passed from one participant to another for action, according to a set of procedural rules.

E-Enterprise Integration - eEI4 Definition of Basic Workflow 4 Workflow Management Coalition (WEMC): provides a common “Reference Model” of workflow management systems to identify workflow management system’s characteristics, terminology and components. 4 Workflow management system is a software system that defines, coordinates, manages, and executes complex business activities.

E-Enterprise Integration - eEI5 Why Petri Nets to Model Workflow? Van der Aalst (1996) -formal semantics despite their graphical nature -can explicitly model states -have abundance of available and theoretically proven analysis techniques 4 Oberweis et al (1997) 4 -Integration of data and behaviour 4 aspects. -Support for concurrent, cooperative 4 processes. -Different degrees of formality -Availability of analysis techniques -Flexibility Merz. Et al (1995) -mathematical foundation -graphical representation -possibility

E-Enterprise Integration - eEI6 Event Why Petri Nets to Model Workflow?

E-Enterprise Integration - eEI7 Petri Nets evolution

E-Enterprise Integration - eEI8 High Level Petri Nets 4 Information Control Nets (ICN) adding a complementary data flow model, generalising control flow primitives and simplifying semantics 4 Coloured Petri Nets in order to enhance the distributed systems architecture Common Open Service Market (COSM), with concurrent workflow modeling. 4 Reconfigurable Nets consists in fact of several Petri Nets which constitute the different possible configurations of the system.

E-Enterprise Integration - eEI9 Introduction 4 First introduced by Carl Adam Petri in A diagrammatic tool to model concurrency and synchronization in distributed systems. 4 Very similar to State Transition Diagrams. 4 Used as a visual communication aid to model the system behaviour. 4 Based on strong mathematical foundation.

E-Enterprise Integration - eEI10 A Petri Net Specification... 4 consists of three types of components: places (circles), transitions (rectangles) and arcs (arrows): –Places represent possible states of the system; –Transitions are events or actions which cause the change of state; And –Every arc simply connects a place with a transition or a transition with a place.

E-Enterprise Integration - eEI11 A Change of State … 4 is denoted by a movement of token(s) (black dots) from place(s) to place(s); and is caused by the firing of a transition. 4 The firing represents an occurrence of the event or an action taken. 4 The firing is subject to the input conditions, denoted by token availability.

E-Enterprise Integration - eEI12 A Change of State 4 A transition is firable or enabled when there are sufficient tokens in its input places. 4 After firing, tokens will be transferred from the input places (old state) to the output places, denoting the new state. 4 Note that the EFTPOS example is a Petri net representation of a finite state machine (FSM).

E-Enterprise Integration - eEI13 Net Structures 4 A sequence of events/actions: 4 Concurrent executions: e1 e2e3 e1 e2 e3 e4 e5

E-Enterprise Integration - eEI14 Net Structures 4 Non-deterministic events - conflict, choice or decision: A choice of either e1, e2 … or e3, e4... e1e2 e3e4

E-Enterprise Integration - eEI15 Net Structures 4 Synchronization e1

E-Enterprise Integration - eEI16 Net Structures 4 Synchronization and Concurrency e1

Online EC transaction example: 17 4 A sequence of as-is events/actions (i.e., INCOME behavior model): 4 A sequence of to-be events/actions: Choose items (place items in shopping cart) Proceed check-out (confirm purchased items) Proceed check-out Login Confirm Purchased items Choose items (place items in shopping cart) Login

Online EC transaction example: 4 To-be behavior model and linkages to object model (SQL data tables!) and organization model (Customers!). Proceed check-out Login Confirm Purchased items Choose items (place items in shopping cart) Product List Custom er List Shopping Cart List

Your web exercise (due on 11/19) –Sample web program: as-is model –Challenge 1 web program: to-be model –Challenge 2 “your own” to-be model E-Enterprise Integration - eEI19

E-Enterprise Integration - eEI20 Stochastic Petri Nets GSPN (Generalized Stochastic Petri Nets) 1.Quantitative analysis 2.Qualitative analysis CGSPN (the Coloured Generalized Stochastic Petri Nets) – which are based on Coloured Petri Nets as pure Petri Net formalism instead of Place/Transition Petri Nets.

E-Enterprise Integration - eEI21 Behavioural Properties Reachability “Can we reach one particular state from another?” Boundedness “Will a storage place overflow?” Liveness “Will the system die in a particular state?”

E-Enterprise Integration - eEI22 Other Types of Petri Nets High-level Petri nets Tokens have “colours”, holding complex information. Timed Petri nets Time delays associated with transitions and/or places. Fixed delays or interval delays. Stochastic Petri nets: exponentially distributed random variables as delays.

E-Enterprise Integration - eEI23 Other Types of Petri Nets Object-Oriented Petri nets Tokens are instances of classes, moving from one place to another, calling methods and changing attributes. Net structure models the inner behaviour of objects. The purpose is to use object-oriented constructs to structure and build the system.

E-Enterprise Integration - eEI24 An O-O Petri Net ready produce Storage accepted consume ready ProducerConsumer send accept Producer data: ITEM ITEM produce( ) void send(ITEM) Consumer data: ITEM ITEM accept( ) void consume(ITEM)

E-Enterprise Integration - eEI25 Application Generators and Very High-Level Languages 4 Allow users to specify the requirements at a very high level of abstraction. 4 In the long term, it would have the highest potential profit. However, it remains very difficult to build generators that scale up to industrial production

E-Enterprise Integration - eEI26 Evaluation 4 Most common approach  black-box reuse 4 The notion of compositionality remains unanswered 4 Questions(which advantages exactly can be achieved or which type of reuse leads to these advantages)remains unanswered

E-Enterprise Integration - eEI27 A Critical Remark Concerning Reuse in the IS-Literature 4 It has remained extremely difficult to realize a systematic approach to reuse. managerial 4 The potential reasons for the lack of systematic reuse ： some technical but many are managerial

E-Enterprise Integration - eEI28 Hidden Assumptions 4 A fundamental problem of software 4 Intended environment (1)implicit (2)don’t match the actual environment or (3)conflict with those of other parts of the system

E-Enterprise Integration - eEI29 Final Remarks very ambitious goal 4 Realizing a systematic form of reuse has proven to be a very ambitious goal ---To reach this goal,good modeling constructs alone have been insufficient 4 Making quick progress towards deciding which modeling constructs are most appropriate 4 Empirical and experimental studies are required(have yet find in the literature)

E-Enterprise Integration - eEI30 Conclusion 4 Identify the existing Patri Net formalisms proposed by various authors 4 Is that even a very good Petri Net formalism for modeling workflows is not worth much if there are no Workflow Management Systems or other computer based on it? 4 V.S database models ： far from being mature 4 Much progress is being made towards developing an adequate modeling construct for modeling workflows using Patri Nets 4 Construct alone isn’t sufficient in IS-field, and how’s in workflow field?