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How to use UML Class Diagram for system Modeling

2025-01-19 Update From: SLTechnology News&Howtos shulou NAV: SLTechnology News&Howtos > Development >

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This article mainly introduces how to use UML class diagram for system modeling, has a certain reference value, interested friends can refer to, I hope you can learn a lot after reading this article, the following let the editor take you to understand it.

How to use UML Class Diagram for system Modeling

Unified Modeling language (UML) is a semi-formal standard for system modeling, which has the characteristics of rigor and flexibility, and can describe different aspects of the system. Taking a power subsystem as an example, this paper introduces the definition of UML class and the relationship between objects, as well as the method of modeling the system through UML class diagram.

Unified Modeling language (UML) is a semi-formal standard for system modeling. Its very strict characteristics can not only meet the requirements of enforceability, but also have flexibility, and can describe all levels of the system. In the most basic case, UML can describe the structural model of a system and the cooperative behavior within the system, as well as the specific behavior specifications of system objects and system components.

Class and UML Class Diagram

A class refers to the low-level structure and behavior specification of a group of objects. The class defines the properties (data elements) and methods (member functions) of the object, and the class can also use state diagrams or activity diagrams to show how its instances respond to various events.

Figuratively speaking, if a class is a "cake cutter", then its object is "cake". An object is an instance of a class, for example, 3.14159 is an instance of a floating-point type. All objects of a particular class have the same data structure and behavior, although their property values may be different from each other.

When we want to describe some structural characteristics of a system, we usually start with its general characteristics, such as the various characteristics of the various components of the system at the time of design and the relationship between them. rather than the system structure at a specific time at runtime. Therefore, we usually abstract the system structure into multiple interrelated classes, and know that instances of these classes may not necessarily exist at all times of operation. If we want to get the state of the system at a certain moment, we need to adopt the object.

Figure 1 shows a power supply system consisting of batteries and solar panels, which is a typical UML class diagram with small boxes representing different classes. The "Power Subsystem" class represents a subsystem, which is a large structural object that contains small objects that provide subsystem functions. The PowerClient class and the Knob class are displayed in "standard form", while the Light class shows some of its properties and methods in addition to its name, its properties are classification color and brightness, and the corresponding enumeration types are COLOR_TYPE and int. Methods to get possible return values and parameters are listed at the bottom of the Light class. DisplayThread is a special class whose instances run in its own thread. The DisplayThread class contains an instance of the Light class, which also runs in the thread of the DisplayThread object.

Usually, the structure model of a system consists of a set of UML class diagrams, some UML class diagrams represent the structure of subsystems, in which the main units are large objects, such as subsystems and components, and other UML class diagrams describe the task structure and focus on active objects (but can also describe system flags and event queues). The rest of the UML class diagrams describe the cooperation structure between classes, that is, how objects work together to achieve system-level behavior or model composition, and mainly describe each model package and their relationships. The above UML class diagrams describe different aspects of the same system architecture.

Object relation

Objects are only part of the system, and they must cooperate with other objects to implement system functions, so links need to be established between objects (usually using C or C++ pointers) in order to invoke services or send events (event) to each other. This is shown as an association between classes in the UML class diagram, and three different associations are shown in figure 1, with lines without arrows representing regular associations. The associations between these classes indicate that they may be active links between instance objects at run time, and services can be invoked between objects. An one-way arrow indicates that the flow of information has only one direction.

A hollow diamond on the line (such as the diamond between the SolarPanel and PositionSensor classes) indicates an aggregation, which represents a form of global and local association. The enhanced form of aggregation is called a combination and is represented by a solid diamond (such as between the power subsystem and the SolarPanel) or by nesting one class within another (such as between the power subsystem and the battery). The combination is the relationship between the whole and the part, but it also shows that the whole class is responsible for the creation and release of each part of the object.

The multiplicity of various associations can also be expressed, that is, the number of instances of a class that the runtime can play a role. For example, you will find that there is only one Knob object associated with each PowerClient object. On the other hand, each power subsystem instance can be associated with 0 or more (represented by *) SolarPanel instances. For nested symbols, the multiplicity of components is shown in the upper-left corner of the widget class. For example, the power subsystem has two battery objects.

In addition to associations, UML defines other relationships between classes. One of the most common is the "decision", or "is-a" relationship, such as the relationship between PowerClient (in a broad sense) and Light (concrete) (that is, Light is a PowerClient). Semantically, "decision" ensures that the Light class also has the properties, operations, and associations of all PowerClient classes. The Light class redefines the operations defined in the PowerClient class, as well as new properties and operations. For example, the Light class has an association with the Knob class because it is defined in its parent class, PowerClient.

In addition, the figure also defines "correctness rules" constraints, which are system semantics that are not defined in the system's classes and associations. In the UML class diagram illustrated in this article, we need to stipulate that only one of the batteries or solar panels can supply power at the same time, but not both. Constraints are used to describe the non-functional characteristics of the system (often referred to as QoS, quality of service), such as the worst and average performance of methods, functions, and so on.

UML is a powerful modeling language used to describe different levels of the system. Its UML class diagram is a flexible graphic symbol, which can clearly express the system structure under different degrees of abstraction. The system level described by UML mainly includes the system architectural units and the relationship between the structural units described in terms of how to support collaboration and the number of instances involved. Additional constraints make it easier for developers to describe the special circumstances and structural limitations of the system structure.

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