基于过程的毂发方法

谁践踏了优雅 2023-07-24 14:35 15阅读 0赞

# 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  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5NzUzNzc4_size_16_color_FFFFFF_t_70]  
Context Data Flow Diagram  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5NzUzNzc4_size_16_color_FFFFFF_t_70 1]

## 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  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5NzUzNzc4_size_16_color_FFFFFF_t_70 2]

# Decompose the System (Process) #

● To break the system into its component subsystems, processes, and subprocesses.  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5NzUzNzc4_size_16_color_FFFFFF_t_70 3]

## Functional Decomposition Diagram ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5NzUzNzc4_size_16_color_FFFFFF_t_70 4]  
● 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.  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5NzUzNzc4_size_16_color_FFFFFF_t_70 5]

## Event Decomposition Diagram ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5NzUzNzc4_size_16_color_FFFFFF_t_70 6]

## 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  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5NzUzNzc4_size_16_color_FFFFFF_t_70 7]

## System Diagram ##

● Events collectively define systems and subsystems.  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5NzUzNzc4_size_16_color_FFFFFF_t_70 8]

## Primitive Diagram ##

● Some (complex) event processes on the system diagram may be exploded into primitive data flow diagram to reveal more detail. ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5NzUzNzc4_size_16_color_FFFFFF_t_70 9]

## 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![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5NzUzNzc4_size_16_color_FFFFFF_t_70 10]  
○ 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: 英国标准协会][BSi_]  
● 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.  
它假设一个系统有一个底层和通用的数据结构，随着时间的推移变化很小，尽管处理要求可能会改变。

## 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

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[BSi_]: https://baike.baidu.com/item/%E8%8B%B1%E5%9B%BD%E6%A0%87%E5%87%86%E5%8D%8F%E4%BC%9A/1212185?fromtitle=BSI&fromid=4681467