System Design and Analysis (4)

content

short answer questions
Modeling Exercises

short answer questions

1. Concept of use case

A use case is a description of how a system responds to external requests in software engineering or systems engineering, and is a technique for obtaining requirements through user usage scenarios. Each use case provides one or more scenarios that describe how the system interacts with end users or other systems, that is, who can use the system for what, to achieve a clear business goal.

2. What is the relationship between use cases and scenarios? What is the main scene or happy path?

There will be many different situations when a use case is actually executed, which is called a use case scenario; it can also be said that a scenario is an instance of a use case. We must cover all use case scenarios when describing a use case, otherwise it may lead to omission of requirements. . In a use case specification, the description of a scenario can be represented by a combination of elementary flows and alternative flows. Scenarios can not only help us prevent the omission of requirements, but also greatly help subsequent development work: developers must implement all scenarios, and testers can design test cases based on use case scenarios.

The main scene or happy path refers to the set of steps that start from the trigger event and execute step by step until the user's interests are met.

3. What are the forms of use cases?

Brief

A short paragraph summary, usually the main success scenario. Get a quick overview of the topic and scope in an early requirements analysis. It may only take a few minutes to create.
Casual
informal paragraph format, containing multiple paragraphs for various scenarios.
Fully

All steps and changes are written in great detail, with supporting sections such as prerequisites and success guarantees. After a number of use cases have been identified and written briefly in the
format, then some (so as 10%) important and high value building use cases are written in great detail during the first requirements workshop.

4. For a complex business, why is it so difficult to write a complete use case?

Because for complex business, there will be many scenarios designed, and the interconnection between scenarios will also complicate use case modeling. At the same time, use case modeling also requires a very familiarity with the scenarios, a certain understanding of the interrelationships between scenarios, and a higher requirement on the modeling ability of the modeler, so it becomes very difficult to compile a complete use case.

5. What is a use case diagram?

A use case diagram is a view that describes the functionality of a system composed of actors, use cases, boundaries, and the relationships between them. A User Case is a model diagram of the functionality of a system as seen by external users (called actors). A use case diagram is a blueprint for a system. A use case diagram presents some actors, some use cases, and their relationships, and is mainly used to model the functional behavior of a system, subsystem, or class.

6. What are the basic symbols and elements of a use case diagram?

The basic symbols and elements of a use case diagram include actors , use cases , subsystems , and relationships

Actor : Represents a user, organization, or external system that interacts with your application or system, often represented by a villain.

Use case : Externally visible system functions, describing the services provided by the system, usually represented by ellipses.

Subsystem : It is used to display part of the function of the system, and this part of the function is closely related.

Relationships : include association<>, generalize<>, contain<>, extend<>

Association: Indicates the relationship between the actor and the use case, the symbol is a straight line, and the actor points to the use case.
Generalization: Indicates the inheritance relationship, the symbol is a straight line with an arrow, and the child use case points to the parent use case.
Contains: Indicates that the current use case includes the functions of other use cases. The symbol is a dotted line with an arrow, pointing to the included use case.
Extension: Indicates the extension of the function of the use case, the symbol is a dotted line with an arrow, pointing to the basic use case.

7. Drawing method and steps of use case diagram

Determining the system for the study

Use the System box of a use case diagram to represent a system under study
Identify Actors

Identify the primary actors/roles who use the system

Identify external systems on which the system depends
Identify use cases (services)

Identify user-level use cases (user goal level)

Identify use cases at the sub function level
Establish the association between Actor and Use Cases

Use a non- directional connection , indicating that there is a two-way interaction protocol between the two

8. What is the value of use case diagrams to stakeholders and developers?

The value of use case diagrams to stakeholders:

The use case diagram can clearly show the function and design of the system, ensure that the design of the system meets the needs of customers, and at the same time allow customers to participate in it, fully communicate with customers, understand customer needs, and improve the functions of the system.
The value that use case diagrams bring to developers:

Use case diagrams can clearly show developers the design process of the system, understand the needs of customers more clearly, clarify the functions and boundaries of the system, and then determine the method and iteration cycle of software development, which is good for software management and improvement. effect.

Modeling Exercises

Choose 2-3 online service systems (or mobile APPs) that you are familiar with with similar businesses, such as hotel reservations (Ctrip, Qunar, etc.), movie ticket reservations, word-reciting APPs, etc., and draw their use case diagrams respectively. and meet the following requirements:
- Please use the user's perspective to describe the user's goal or the service provided by the system
- Granularity down to the sub-case level and associating them with include and exclude
- Please color-coded use cases or sub-use cases that you think are innovative (different from competitors)
- Identify external systems and services as much as possible
Then, answer the following questions:
1. Why are use case diagrams similar for similar systems?
2. If it is a hotel reservation business, please compare the Asg_RH use case diagram, and briefly describe how to use the use case diagrams of products in different eras and different regions to display and highlight innovative businesses and technologies
3. How to use the use case diagram to locate the role of innovative ideas (business innovation, or technological innovation, or business model innovation) in the system
4. Please use the SCRUM method, select a use case diagram, and prepare a development plan for the requirements (backlog) developed by a certain hotel.
5. According to Task 4, refer to Estimating Software Costs Using Use Case Points to give an estimate of the project use case points

Wanda Movies App
Hundred Words Slash App

Answer question:

Because the scenarios that similar systems need to deal with are often similar, such as booking tickets and buying things, you need to pay, and when it comes to booking, you often need to locate a specific location. Both must be implemented, so the use case diagrams are often similar.
In different eras, users in different regions have different needs for hotels. Therefore, with the evolution of the era, the algorithm of the hotel's review system and recommendation system can be updated. Different regions, such as religious regions, tourism and cultural regions, etc. Add some appropriate filtering functions.
If the innovative idea is the parent node in the use case diagram, the breakthrough and effect of the innovation are relatively large, and if it is an included use case or a sub-use case, the innovation is relatively small.
The backlog of the hotel use case diagram in the class

Id	Name	Imp	Is
1	Find hotel	30	5
2	Make reservation	30	10
3	Manage basket	90	16
4	Pay	70	8
5	Login	80	16

According to the user point approach, the criteria for assigning weights to use cases are:

Simple use case: 1 to 3 transactions, weight=5
General use case: 4 to 7 transactions, weight=10
Complex use case: more than 7 transactions, weight=15

example	affairs	calculate	UC weight
1 Find hotel	3	5	Simple
2 Make reservation	5	10	generally
3 Manage basket	5	7	generally
4 Pay	2	5	Simple
5 Login	4	8	generally