Case study of software exam system architecture (software engineering related concepts)

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Column:System Architect

1. Differences and connections between flow charts and data flow diagrams

Flowchart: Graphically displays the logical process of the application from data input to output, describing the control flow of the processing process.

Data flow diagram: As a graphical tool, it is used to illustrate the business processing process, the functions contained within the system boundary and the data flow in the system.

The main differences between the two include:
(1) The processing process in the data flow diagramcan be parallelized;The flow chart can only be in one processing process at a certain point in time.
(2) The data flow diagram shows the system's data flow; the flow chart shows the system's Control flow.
(3) The data flow diagram shows the global processing process, and the processes follow different timing standards; flow chart Processing follows consistent timing standards. (4) Data flow diagram is suitable for the logic modeling stage of system analysis; flow chart is suitable for system design in thephysical modeling stage.

2. The meaning and difference between state diagram and activity diagram

State chart: Mainly used to describe the dynamic behavior of an object during its lifetime, showing the state sequence experienced by an object, the events that cause state transition, and Actions accompanying state transitions.

Activity diagram can be used to describe the workflow and concurrent behavior of the system. Activity diagram can actually be regarded as a special form of state diagram. After one activity in the activity diagram ends, it will immediately enter the next activity (in the state diagram, the transfer of state may require the triggering of events).

The biggest difference between the two is:
The state diagram focuses ondescribing the results of the behavior, while the activity The diagram focuseson the actions that describe the behavior. Secondlyactivity diagrams can describe concurrent behaviorwhile statecharts cannot.

3. The difference between activity diagram and flow chart

• The activity diagram describes the rules followed by the sequence relationship of object activities. It focuses on showing the behavior of the system rather than the processing process; while the flow chart focuses on describing the processing process.

• Flowcharts are generally limited to sequential processes, while activity diagrams can support concurrent processes.

• Activity diagrams are object-oriented, while flowcharts are process-oriented.
  
  

4. Basic elements contained in data flow diagrams and their functions

Data flow: Data flow is the path that data travels within the system, and therefore consists of a set of data with fixed components.

External entities: Represents entities outside the system, which can be people, things or other software systems.

Processing (processing): Processing is a unit that processes data. It receives certain data input, processes it, and produces output.

Data storage: Represents the static storage of information, which can be a file, a part of a file, an element of a database, etc.

5. Balance principle of data flow diagram:

(1) The balance between the subgraph and the parent graph:
means that the input/output data flow on the boundary of any DFD subgraph must be processed corresponding to its parent graph Input/output data flow remains consistent.

If a data flow for a certain process in the parent graph corresponds to several data flows in the subgraph, and all the data items that make up these data flows in the subgraph are exactly equal to this data flow in the parent graph, then they are still balanced. of.

(2) Inside the subgraph: The input and output of processing need to be balanced.
 Among them, there are three common errors in data flow diagrams:

• [Black Hole] A process has only input data flow but no output data flow.
• [Miracle] A process only has an output data stream but no input data stream.
• [Gray Hole] If a processed input data stream cannot be processed to produce an output stream.
  
  

6. Relationship between use cases

The main relationships between use cases areGeneralization, Include and Extend.

(1) When common behavior can be extracted from two or more use cases, it can be expressed using an inclusion relationship.

(2) If a use case mixes two or more different scenarios, that is, multiple branches may occur depending on the situation, the use case can be divided into a basic use case and one or more extended use cases.

(3) When multiple use cases share a similar structure and behavior, their commonality can be abstracted into a parent use case, and other use cases can be used as child use cases in a generalization relationship.

7. The relationship between classes and their basic meanings

Dependency: Changes in one thing affect another thing.

Generalization relationship: Special/general relationship.

Association: Describes a set of chains, which are connections between objects.

Aggregation relationship: The life cycle of the whole and the part are different.

Combined relationship: The life cycle of the whole and the part is the same.

Implementation relationship: The relationship between interface and class.

8. The meaning of object model, dynamic model and functional model and the relationship between them

• Object model: used to describe the system data structure.
• Dynamic model: used to describe the system control structure.
• Functional model: Used to describe system functions.

These three models all involve common concepts such as data, control, and operation, but have different emphases. They reflect the substantive content of the system from different aspects, and together they comprehensively reflect the requirements for the target system.

The functional model specifies what the system should "do"; the dynamic model clearly specifies when to do it; and the object model defines the entities that do things.

9. Design categories are usually divided into three categories. The responsibilities of these three categories are:

(1)Entity class. The entity class maps each entity in the requirement and saves the information that needs to be stored in permanent storage, such as users, products, etc.

(2)Control class. A control class is a class used to control the work of a use case and is used to model the control behavior unique to one or several use cases. For example, settlement, stocking, etc.

(3)Border class. Boundary classes are used to encapsulate the information or data flow that flows inside and outside the use case. For example, browser, shopping cart, etc.

10. Classification of non-functional requirements and their meaning

• Operational Requirements: Refers to the operating environment requirements required for the system to complete tasks and how to meet possible future changes in system requirements.
• Performance Requirements: Indicators for system performance requirements. Common ones include: response time, throughput rate.
• Security Requirements: Protective measures or precautions needed to prevent system crashes and ensure data security.
• Cultural Requirements: The unique requirements for the system put forward by different user groups using this system.

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Column:System Architect