UML Diagram: Class Diagram-Pitaya Software

UML Diagram: Class Diagram

Zu Tao ，Pitaya System Engineering

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2020-2-13

Why do you need class diagram modeling?

Class diagrams are the crystallization of object-oriented thinking, which describes things in the objective world from the perspective of objects:

An object is an objective world being that occupies space // such as a wheel
External performance characteristics // e.g. radius of wheels
It interacts with the outside
An object may be made up of smaller objects, like molecules with atoms inside them;
One object may have a link to another
... ...

There are many objects in the real world, and in order to describe them concisely and make it easier to communicate, people abstract several similar objects into classes:

Classes exist only in the human mind, in the human language,，
Give the class a name that reflects the instance of the object it represents
Describe the characteristics of an object with attributes
Methods describe the behavior of an object
A class of a partial object can make up a class of an entire object
A class can be associated with another class
Several similar classes can be abstracted as parent classes
... ...

The relationships between objects are abstracted into the relationships of classes: association, aggregation, composition, generalization, implementation, and so on.

It's a bit abstract to say, for example.

When we are faced with complex logical descriptions, the process of reading is actually the process of understanding various concepts and relationships, and object-oriented analysis methods and class diagrams can greatly improve the efficiency and accuracy of understanding.

The following is a functional description of a motor control system, which the engineer described in text language as follows:

Description of the function

The operator issues control commands to the controller, which starts the motor

If the conditions are met, the motor starts up with a success message to the operator
If the conditions are not met, a warning message is fed back to the operator

There are two types of motors, DC motors and AC motors, and the starting conditions for voltage determination are different

If the DC motor, the voltage reaches 100 volts to start
If the AC motor, the voltage reaches 200 volts to start

If the relevant concepts are modeled with a class diagram, the model is as follows:

Which is better?

Easier to understand
More comprehensive
It is easier for developers to translate into system implementations.

I guess readers can judge for themselves based on their intuition!

What is there in the class diagram

Any UML diagram has semantics, elements, relationships, and uses, and the following is a list of class diagrams:

Semanteme	Describe the class, its properties and methods, and the relationships between the classes
Element	Kind (class), interface, abstract class
Relationship	Relationships between classes: Association-association, aggregation-aggregation, composition-compose Dependency-dependency Generalize-generalize Relationship between classes and interfaces: Realization
Use	Classify objects in the objective world, describe features with attributes, describe behaviors with methods, and model the relationship between classes to help users: Conceptual modeling Data modeling Design class modeling Implement class modeling

Legend: Domain model

The class diagram can be used to perform object-oriented analysis of the problem domain, analyze the properties, methods, and relationships of various domain objects, and establish a domain model (also called an analytical model), as shown in a simplified example of a domain model:

Legend: Design modelsnake game class diagram

In order to make the reader look more vivid, the use of legends to introduce the use of class diagrams, the following is the design class diagram of the snake game. The difference between the design class diagram and the analysis class diagram is that the software implementation environment of the computer and the development language mechanism are considered, and a logical view of the solution is given from the development perspective:

In order to achieve software robustness, design class diagrams often use design principles, such as the following:

Based on the principle of single responsibility, Map and Food are separated.
Based on the principle of interface isolation, the interface Movable is abstracted.
Based on the principle of dependency inversion, the interface Movable is placed on the same layer as the Map.

Class Diagram Description:

The following is a description dictionary of a class generated from a class diagram:

Serial number	Kind	Illustrate
1.	Timer	The timer class has a method tick, and when the time is up, the whole method is triggered - the mobilization object Move().
2.	Map	Map class, with attributes weight, height, color, cellSize; Has the method CreateFood().
3.	Movable	An interface that can represent a movable object, with the method declaration Move().
4.	Animal	The animal class is an abstract class with attributes Length and integrals, with the abstract method Move().
5.	Node	Node class, with properties pointX, pointY, size, color; Has the method Draw().
6.	Food	The food class has the attributes name and score.
7.	Alligator	Crocodile, with the property food and method move(), inherits the Animal class.
8.	Snake	Snakes, with the method Move(), inherit from the Animal class.
9.	Train	Train class, with method Move().
10.	Direction	Directional enumeration type, with values up, down, right, left.
11.	Color	Color enumeration type with multiple colors: Red, Green, Blue, Orange, Black.

The following is a directory of relationships between classes generated from the class diagram:

Serial number	Start class	Relationship	Endpoint class
1.	Map	Association	Movable
2.	Direction	Aggregation	Movable
3.	Animal	Realisation	Movable
4.	Node	Aggregation	Animal
5.	Food	Generalization	Node
6.	Node	Aggregation	Map
7.	Train	Realisation	Movable
8.	Timer	Dependency	Movable
9.	Alligator	Generalization	Animal
10.	Snake	Generalization	Animal
11.	Node	Association	Color

You can generate code based on class diagrams, as follows the code generated based on class diagrams (C++ language)

You can generate a data model based on a class diagram and then generate DDL code based on the data model. Here's the data model generated from the class diagram: