Structured Analysis Design-[Soft exam afternoon Questions]

Structured Analysis is a data flow-Oriented Requirement analysis method. The idea is to break down layer by layer from top to bottom. It consists of the following parts: data flow chart, data dictionary, processing logic description, and supplementary materials.

1. Data Flow Diagram (DFD): [concept]

Data Flow digoal is a graphical tool that is easy to understand and analyze data flows.

Element]

name	graphic operator	concept
external entity	□	people and organizations outside the system, data sources, or endpoints
processing	○	the conversion between the input stream and the output stream, contains names and numbers (determining layers, graphs, and subprocesses)
data storage	〓	store data with a name
Data Stream	->	Fixed component data, indicating data flow direction, non-control flow. Names are required except for those related to storage.

[Painting method]

1) Top-layer graph: entity-input stream-big processing (system)-output stream-entity

2) layer-0 graph: Decomposition Processing

Key: A. Confirm processing: add processing where the composition and value of the data stream change.

B. Determine the data stream: the user regards a number of data as a whole.

3) subgraphs: processing is considered as a small system internally, which is simple enough.

4) numbers are required for graph and processing.

Principle: A parent has more than one child, and the top layer has only one child. The subgraph number = the parent image processing number.

[Note]

Proper Name

Data Flow non-Control Flow

Processing must have input and output streams with different names.

Parent graph subgraph balancing.

Keep data Conservation

[Instance]

 

 

Ii. Data Dictionary
[Role]

Description of data in the database.

[Include]

Data items, data structures, data streams, data storage and processing.

[Details]

Data item description = {data item name, description, alias, data type, length, value range, value meaning, logical relationship with other data items}

Data Structure Description = {Data Structure name, description, composition: {data item or data structure }}

Data Stream description = {data stream name, description, data stream source, data stream destination,

Composition: {data structure}, data volume, peak traffic}

Data storage description = {data storage name, description, number, inbound data stream, outbound data stream

Composition: {data structure}, data volume, access method}

Processing description = {processing name, description, input: {data stream}, output: {data stream}, processing {brief description }}

Iii. Summary decomposition and abstraction are two basic methods for people to control the complexity of problems. Structured design is not only the focus of the soft test, but also the basis for our future software design. The high-level data flow diagram is abstracted to reflect the overall appearance of the system. The high-level data flow diagram is decomposed by the high-level processing, which makes the implementation of local processing more feasible.

Structured Analysis Design-[Soft exam afternoon Questions]