Process Modeling
Process Modeling
● A technique for organizing and documenting the structure and flow of data through a system’s processes and/or the logic, policies, and procedures to be implemented by a system’s processes.
● Data Flow Diagram (DFD) - a process model used to depict the flow of data
through a system and the work or processing performed by the system.
Process Modeling Toolbox
● [DFD] Context Data Flow Diagram
● Functional Decomposition Diagram
● Event-Response / Use Case List
● Event Decomposition Diagram
● [DFD] Event Diagram
● [DFD] System Diagram
● [DFD] Primitive Diagram
Student Information System
Context Diagram
Context Data Flow Diagram
Context Data Flow Diagram
● External Agent - an outside person, organization unit, system, or organization that interacts with a system. Also called external entity.
○ VS Actor in use case diagram
● Process - work performed on, or in response to, incoming data flows or conditions.
○ A system is a process
● Data Flow - data that is input or output to or from a process
Decompose the System (Process)
● To break the system into its component subsystems, processes, and subprocesses.
Functional Decomposition Diagram
● The root process corresponds to the entire system.
● The system is initially factored into subsystems and/or functions.
● We like to separate the operational and reporting aspects of a system. Later, if the structure doesn’t make sense, we can change it.
Figure out Events or Use Cases
● To determine what business events the system must respond to and what responses are appropriate.
● Event types
○ External events
○ Temporal events
○ State events
● Use cases is a technical to find and identify events and responses.
Event Decomposition Diagram
Event Diagram and Data Structure
● Event Diagram - a data flow diagram that depicts the context for a single event
● Data Store - an “inventory” of data. It stores data intended for later use
● Data Structure - a specific arrangement of data attributes that define a single instance of a data flow
System Diagram
● Events collectively define systems and subsystems.
Primitive Diagram
● Some (complex) event processes on the system diagram may be exploded into primitive data flow diagram to reveal more detail. 
Rules for Data Flows
● A data flow should never go unnamed
● In logical modeling, data flow names should describe the data without describing the
implementation
● All data flows must begin and/or end at a process
Common Errors on DFDs
● A process has inputs but no output - black hole
● A process has outputs but no input
● The inputs are insufficient to produce the output
Describe Process Logic
● Process Logic
○ Structured English
○ Decision Table
The Process of Logical Process Modeling
● Draw context DFD to establish initial project scope.
● Draw functional decomposition diagram to partition the system into subsystems.
● Create event-response or use-case list for the system to define events for
which the system must have a response.
● Draw an event DFD (or event handler) for each event.
● Merge event DFDs into a system diagram (or, for larger systems, subsystem diagrams).
● Draw detailed, primitive DFDs for the more complex event handlers.
● Document data flows and processes in data dictionary.
Structured Analysis and Design
SSADM: A Top-Down Approach
● A British standard BSi: 英國標準協會
● SSADM made mandatory for all new information system developments in 1983
● Renamed as “Business System Development” in 2000
● Focus on data and process
SSADM Basic Assumption
● It assumes that a system has an underlying and generic data structure which
changes very little over time, although processing requirements may change.
它假設一個系統有一個底層和通用的數據結構，隨着時間的推移變化很小，儘管處理要求可能會改變。
SSADM Techniques
● Logical Data Modeling - ERD ( entity relationship diagram， will covered by data modeling)
● Data Flow Modeling - DFD
● Entity Event Modeling - ELH (event life history)
https://en.wikipedia.org/wiki/Structured_systems_analysis_and_design_method
Some Important Characteristics of SSADM
● Dividing a project into small modules with well defined objectives
● Useful during requirements specification and system design stage
● Diagrammatic representation and other useful modeling techniques
● Simple and easily understood by clients and developers
● Performing activities in a sequence
SSADM Stages
● Determining feasibility
● Investigating the current environment
● Determining business systems options
● Defining requirements
● Determining technical system options
● Creating the logical design
● Creating the physical design
Readings
● Your textbook
○ Chapter 9