flow和process区别

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mob64ca14150f43 2024-11-22 10:17:35

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flow和process区别_数据流图中flow不显示文字

A data flow diagram (DFD) is a graphical representation of the "flow" of data through an information system, modelling its process aspects. A DFD is often used as a preliminary step to create an overview of the system, which can later be elaborated. DFDs can also be used for the visualization of data processing (structured design).
Data flow diagrams (DFDs) reveal relationships among and between the various components in a program or system. DFDs are an important technique for modeling a system’s high-level detail by showing how input data is transformed to output results through a sequence of functional transformations. DFDs consist of four major components: entities, processes, data stores, and data flows. The symbols used to depict how these components interact in a system are simple and easy to understand; however, there are several DFD models to work from, each having its own symbology. DFD syntax does remain constant by using simple verb and noun constructs. Such a syntactical relationship of DFDs makes them ideal for object-oriented analysis and parsing functional specifications into precise DFDs for the systems analyst.
DFDs consist of four basic components that illustrate how data flows in a system: entity, process, data store, and data flow.
Entity
An entity is the source or destination of data. The source in a DFD represents these entities that are outside the context of the system. Entities either provide data to the system (referred to as a source) or receive data from it (referred to as a sink). Entities are often represented as rectangles (a diagonal line across the right-hand corner means that this entity is represented somewhere else in the DFD). Entities are also referred to as agents, terminators, or source/sink.
Process
The process is the manipulation or work that transforms data, performing computations, making decisions (logic flow), or directing data flows based on business rules. In other words, a process receives input and generates some output. Process names (simple verbs and dataflow names, such as “Submit Payment” or “Get Invoice”) usually describe the transformation, which can be performed by people or machines. Processes can be drawn as circles or a segmented rectangle on a DFD, and include a process name and process number.
Data Store
A data store is where a process stores data between processes for later retrieval by that same process or another one. Files and tables are considered data stores. Data store names (plural) are simple but meaningful, such as “customers,” “orders,” and “products.” Data stores are usually drawn as a rectangle with the righthand side missing and labeled by the name of the data storage area it represents, though different notations do exist.
Data Flow
Data flow is the movement of data between the entity, the process, and the data store. Data flow portrays the interface between the components of the DFD. The flow of data in a DFD is named to reflect the nature of the data used (these names should also be unique within a specific DFD). Data flow is represented by an arrow, where the arrow is annotated with the data name.

数据流图（Data Flow Diagram）：简称DFD，它从数据传递和加工角度，以图形方式来表达系统的逻辑功能、数据在系统内部的逻辑流向和逻辑变换过程，是结构化系统分析方法的主要表达工具及用于表示软件模型的一种图示方法。

数据流图是结构化分析方法中使用的工具,它以图形的方式描绘数据在系统中流动和处理的过程，由于它只反映系统必须完成的逻辑功能，所以它是一种功能模型。在结构化开发方法中，数据流图是需求分析阶段产生的结果。

数据流图或数据流程图（Data Flow Diagram），缩写为DFD。数据流图DFD是描述系统中数据流程的一种图形工具，它标志了一个系统的逻辑输入和逻辑输出，以及把逻辑输入转换逻辑输出所需的加工处理。

值得注意的是，数据流图不是传统的流程图或框图，数据流也不是控制流。数据流图是从数据的角度来描述一个系统，而框图是从对数据进行加工的工作人员的角度来描述系统。

DFD显示系统将输入和输出什么样的信息，数据如何通过系统前进以及数据将被存储在何处。它不显示关于进程计时的信息，也不显示关于进程将按顺序还是并行运行的信息，而不像传统的关注控制流的结构化流程图，或者UML活动工作流程图，它将控制流和数据流作为一个统一的模型。

数据流图可以在SDLC的分析和设计阶段使用。

根据层级数据流图分为顶层数据流图、中层数据流图和底层数据流图。除顶层数据流图外，其他数据流图从零开始编号。
顶层数据流图只含有一个加工表示整个系统；输出数据流和输入数据流为系统的输入数据和输出数据，表明系统的范围，以及与外部环境的数据交换关系。
中层数据流图是对父层数据流图中某个加工进行细化，而它的某个加工也可以再次细化，形成子图；中间层次的多少，一般视系统的复杂程度而定。
底层数据流图是指其加工不能再分解的数据流图，其加工称为“原子加工”。
Difference Between Flowchart and Data Flow Diagram (DFD)
• The main difference between flow chart and data flow diagram is that flow chart presents steps to complete a process where as data flow diagram presents the flow of data.
• Flow chart does not have any input from or output to external source whereas data flow diagram describes the path of data from external source to internal store or vice versa.
• The timing and sequence of the process is aptly shown by a flow chart where as the processing of data is taking place in a particular order or several processes are taking simultaneously is not described by a data flow diagram.
• Data flow diagrams define the functionality of a system where as flow diagram shows how to make a system function.
• Flow charts are used in designing a process but data flow diagram are used to describe the path of data that will complete that process.
What are 0-level data flow diagrams?
A level 0 data flow diagram (DFD), also known as a context diagram, shows a data system as a whole and emphasizes the way it interacts with external entities. This DFD level 0 example shows how such a system might function within a typical retail business.
Data flow diagramming is a highly effective technique for showing the flow of information through a system. DFDs are used in the preliminary stages of systems analysis to help understand the current system and to represent a required system. The DFDs themselves represent external entities sending and receiving information (entities), the processes that change information (processes), the information flows themselves (data flows), and where information is stored (data stores). The hierarchical DFDs consist of a single top layer (Level 0 or the context diagram) that can be decomposed into many lower level diagrams (Level 1, Level 2…Level N), each representing different areas of the system.
DFDs are extremely useful in systems analysis as they help structure the steps in object-oriented design and analysis. Because DFDs and object technology share the same syntax constructs, DFDs are appropriate for the OO domain only.
DFDs are a form of information development, and as such provide key insight into how information is transformed as it passes through a system. Having the skills to develop DFDs from functional specs and being able to interpret them is a value-add skill set that is well within the domain of technical communications.