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Petri net-based modelling of workflow system ： An overview

Petri net-based modelling of workflow system ： An overview. Professor ： Dr. Ou-Yang Reporter ：陳星豪 李高樺 洪淨池 魏廷璋. Outline. 1.Introduction 2. Workflow and workflow management system 3. Petri nets 4. Petri net-based workflow modeling 5. Petri net-based workflow software. Introduction.

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Petri net-based modelling of workflow system ： An overview

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  1. Petri net-based modelling of workflow system：An overview Professor：Dr. Ou-Yang Reporter：陳星豪 李高樺 洪淨池 魏廷璋

  2. Outline 1.Introduction 2. Workflow and workflow management system 3. Petri nets 4. Petri net-based workflow modeling 5. Petri net-based workflow software

  3. Introduction

  4. Introduction • The core of workflow system is the notion of business process, which is a set of activities with a common goal • Workflow符合企業先前定義的需求，支援執行一連串需要使用人力以及各種資源的活動

  5. Introduction • Petri nets are applied in different discrete-event dynamic systems, which are characterised by parallelism and synchronization • Petri nets-based modelling and analysis of workflow and workflow system is an active research area in academic • A small number of vendor have developed Petri nets-based workflow management system （WfMS）

  6. Workflow and workflow management system

  7. Workflow and workflow management system • 1970年代，workflow的概念從工廠自動化的觀念中延伸而出，第一個workflow的雛形被發展出來 • 1970～1980年間，Backtalk、Office Talk-P、Office Information System是最早發行的workflow系統雛形 • 1980年代晚期開始，WfMS和ㄧ些computer-based system進行結合，例如：DBMS、document imaging或e-mail

  8. Workflow系統特徵 • 一個workflow本身就是一個流程，使文件、資訊或工作在一個與多個參與者之間傳遞，共同協調執行，涵蓋到組織之間與內部的資訊流和控制流 • Workflow Management Coalition • A Workflow as a computerised-based facilitation or automation of business process, in whole or part • A specific software system, WfMS, manages and executes workflow through the execution of software whose order of execution is driven by a computer representation of the workflow logic

  9. Workflow系統特徵 • WfMS由兩元件所組成 • The workflow model（process definition） • The workflow execution module（workflow enactment service ）

  10. Workflow system component and phases

  11. Workflow型態 • 以流程定義與工作派工來看，有三種型態workflow • Production workflow • 固定的工作定義與執行次序 • Administrative workflow • Cases 大致遵循原本已定義完成的程序，但是有另一條途徑供選擇 • Ad hoc workflow • 以事先定義的流程樣版來驅動cases進行 • 流程樣版能被修正以符合某些特定cases的需求

  12. Petri nets

  13. Petri nets • 一種modelling工具，由Petri所建構 • 圖形化概念具有自我文件化(self-documenting)的能力，成為從事設計流程的有力工具 • 建立數學模式來描述系統的行為 • 驗證模式 • 適用於離散事件動態系統（discrete event dynamic systems）的modelling與分析，具有平行與同步作業的特性

  14. Petri nets • Three structural components • Places • Transitions • Arcs • Places以圓圈表示，代表系統的狀態與條件 • Transitions以長柱形或長盒形表示，描述可能改變系統狀態的事件 • Places與Transitions之間的關係以單一方向之Arcs連結 • 兩個相同型態的節點之間不能相互連結 • 系統的動態行為可以用tokens來呈現

  15. Petri nets • Petri nets的正式定義為 • A Petri net is a 4-tuple N = {P, T, F, M0} M which represents a state of the modelled system is a distribution of tokens over the set of places

  16. Petri net model of workflow

  17. Petri nets • Two classes of properties of Petri net-based model system • Behavioural or marking dependent properties • Depending on the initial marking of the model • Structural properties • Relate to the structure of the modeled system and independent of the initial marking

  18. Petri net-based workflow modeling

  19. Workflow modelling • It is criticized that they have • no needed functionality • no clear set of definition • no general conceptual model

  20. Petri net-based workflow modeling • Zismann第一次應用Petri nets在辦公室流程上，為workflow系統的早期想法 • Ellis延伸Zismann，推出Information Control Net (ICN)，並且應用在辦公室資訊系統的建構 • Vander Aalst已經證實workflow可以與Petri net完全結合 • Vander Aalst提出workflow有三種不同的維度：process、case以及resource

  21. Petri net-based workflow modeling • 每一個workflow的工作由transition呈現 • Places則是描繪出一個需執行任務之pre-condition與post-condition，或是所需的資源 • 弧線表達出任務之間的邏輯關係以及它的流向 • Example

  22. Petri net model of workflow

  23. Resource modeling of workflow • 前ㄧ模式只是描繪出一個workflow流程的單一instance，沒有討論到時間或資源的觀點 • 實際的情況下，每一個流程可能需要執行超過一個以上的instance • Example

  24. Resource modeling of workflow

  25. Petri net-based workflow software

  26. Petri net-based workflow software • Protos • to export the processes modeled with Protos into some WfMS products such as COSA and FLOWer • Structware • a tool that allows the designer to design and simulate business processes based on Petri net models.

  27. Petri net-based workflow software • ExSpect • a business process modeling tool, able to model and analyze workflow processes in terms of Petri nets • Woflan • interfaces with the other commercial workflow products such as COSA , Staffware and Protos • INCOME

  28. Modelling and qualitative analysis of workflow • qualitative analysis • deadlock freeness • the correct flow of the work • absence of overflow • the presence of certain mutual exclusion wherever shared resource are used • mainly concentrated on structural modelling and analysis of the qualitative properties of workflow processes

  29. Temporal Constraint Petri Net(TCPN) • a modified version of an ordinary Petri net • has been used to model workflow application at conceptual level and as a test-bed to verify the system properties. • Each task is decomposed into some primitives and therefore the states between the primitives can be represented. Task dependencies are categorized into control-flow dependency, value dependency and external dependency

  30. Business Procedure net (BP-net) • Free software • It is proposed for representation, validation and verification business processes. • Then this model has been modified into a workflow net (WF-net) as a sound model for workflow • In order to obtain a strong sound workflow model, he has added 1-safe property to WF-net

  31. Workflow Authorization Model • This model ensures that in a workflow system, authorized resources are granted privileges on required tasks only while the task is being executed

  32. Inter-Organizational Workflow • Inter-organizational workflow and the availability of the Internet have affect workflow technology • SGML • A Petri net structure as a base layer • can be used in a distributed environment • CPN-based Colored Petri-Net

  33. Workflow Fragmentation • Ad hoc changes • related to rare events • Radical changes • Evolutionary changes • are often the outcomes of reengineering the system

  34. Object Oriented Modeling • Modular Process Nets • Higher-Order Object Net (HOON) • Business Process Petri nets (BPP-nets)

  35. GSPN • The one that mostly has been used • Continuous Time Markov Chain • Time • Conversion

  36. GSPN Modeling

  37. Standard Petri-net

  38. GSPN

  39. Petri nets • OCPN(Object Composition Petri nets) • XOCPN (eXtended Object Composition Petri Net) • DOCPN (Distributed Object Composition Petri Net) • TSPN (Time Stream Petri Net)

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