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UML consists of graphs and metamodels. Graphs are syntax and metamodels are semantics. UML mainly consists of three basic building blocks: Things, Relationships and Diagrams. In this series, we will introduce these basic components of UML and UML tools and applications, so that readers can form a preliminary overall impression of UML. In the following series, several examples are used to gradually unfold these contents.

Basic Building blocks of 1.1UML Modeling language

1.1.1 things

Things are the final result of entity abstraction and the basic members of the model. UML modeling language includes structural things, behavioral things, grouped things and annotated things.

(1) structural things (Structuralthings)

Structural things are the static parts of the model, which are used to present the representation elements of concepts or entities. They are the most common elements in software modeling. There are seven kinds of them:

Class: a class is a collection of objects that have the same properties, methods, relationships, and semantics

Interface (Interface): an interface refers to the services (operations) provided by a class or component, describing the visible actions of the class or component

Collaboration: collaboration describes a set of classes and their associated collections that collaborate to accomplish a particular task, which are used to model the implementation of a use case

Use case (UseCase): a use case defines a business goal achieved by the interaction between the executor (the person who interacts with the system outside the system) and the system being considered.

Active class (ActiveClass): the object of the active class has one or more processes or threads. An active class is very similar to a class, except that the behavior of the element represented by its object exists at the same time as other elements.

Component: a component is a physical, replaceable part that contains a collection of interfaces, such as COM+, JAVABEANS, etc.

Node: a node is a physical element that exists when the system is running, representing a computable resource, which usually takes up some memory and has processing power.

(2) behavior things (Behavioralthings)

The behavior thing in UML modeling language refers to the dynamic part of the UML model, which represents the "verb" in the sentence, represents the part of the model that changes with time and space, and includes two categories:

Ineraction: an interaction consists of a series of messages exchanged between a group of objects in a specific context to achieve a specific purpose.

State machine (statemachine): a state machine consists of the states of a series of objects.

(3) grouped things (Groupingthings)

You can think of grouped things as a "box" in which the model can be decomposed. At present, there is only one grouped thing, namely package. Structural things, action things, and even grouped things can all be put in a package. Packages are purely conceptual and exist only in the development phase, while components exist at run time.

(4) annotate things (Annotationalthings)

Annotated things are the explanatory part of the UML model.

1.1.2 relationship

Relationships are the way things are connected, and four relationships are defined in the UML modeling language:

(1) Dependencies: the semantic relationship between two things, in which a change in one thing affects the semantics of the other.

(2) Association: a structural relationship that describes the connection between a group of objects, such as aggregation (describes the structural relationship between the whole and the parts)

(3) Generalization: a generalization-specialization relationship

(4) Realization: the semantic relationship between classes in which one class specifies a contract guaranteed by the other class.

1.1.3 figure

A graph is a classification of a collection of things, and the UML modeling language contains a variety of graphs:

(1) Class diagram (ClassDiagram): class diagram describes the classes contained in the system, the internal structure of classes and the relationship between classes.

(2) ObjectDiagram: an object diagram is a concrete example of a class diagram

(3) PackageDiagram: the package diagram shows the package and the dependency class diagram between them.

(4) component diagram (CompomentDiagram, also known as component diagram): component diagram describes the physical structure of code components and the dependencies between them.

(5) deployment diagram (DeploymentDiagram): deployment diagram defines the physical architecture of software and hardware in the system.

(6) use case diagram (UsecaseDiagram): from the user's point of view, the use case diagram describes the functions and requirements of the system, and shows the relationship between various roles outside the system and various use cases within the system.

(7) sequence diagrams (SequenceDiagram): sequence diagrams represent dynamic cooperative relationships between objects.

(8) collaboration diagram (CollaborationDiagram): cooperation diagram describes the cooperative relationship between objects.

(9) State diagrams (StatechartDiagram): state diagrams describe all possible states of a class of objects and the transition conditions of states when events occur.

(10) activity diagrams (ActivityDiagram): activity diagrams describe the execution sequence of various activities in the system.

Tools and applications of 1.2UML Modeling language

"if you want to do good work, you must first benefit from the tools." in order to make effective use of UML, we need to first obtain a UML tool software.

At present, the most widely used UML modeling tool in the industry is RationalRose. Forward (generating the corresponding code for the model), reverse (deriving the model of the system from the user's original software system) and two-way engineering (realizing the cyclic engineering between the model and the code) can be realized in RationalRose, so as to ensure the high consistency between the model and the code. RationalRose supports C++, VisualC++, Java, Smalltalk, Ada, VisualBasic, PowerBuilder and other languages and development tools, and can generate interface definition language (IDL) for CORBA applications and database description language (DDL) for database applications. In addition, RationalRose provides good support for team development and standardized development process management.

For small-scale applications, we can use Visio in Microsoft's Office suite, which provides support for drawing various UML diagrams.

From an application point of view, object-oriented system design generally needs to complete the following work:

(1) describe the requirements

(2) establish the static model of the system according to the requirements.

(3) describe the behavior of the system.

The models established in (1) and (2) are static (using use case diagrams, class diagrams, object diagrams, component diagrams and deployment diagrams, etc.) and are static modeling mechanisms in the standard modeling language UML, while the models established in (3) represent the sequence, state or interactive relationships at execution time (described by state diagrams, activity diagrams, sequence diagrams and collaboration diagrams) and are dynamic modeling mechanisms in the standard modeling language UML.

It can be seen that the main contents of the standard UML modeling language can also be divided into two categories: static modeling mechanism and dynamic modeling mechanism.

In addition, it is important to note that UML is only a modeling language, which is independent of the specific modeling process. Therefore, when it is convenient for modeling, it can follow any type of modeling process. Nevertheless, the authors of UML recommended RUP (RationalUnifiedProcess) for us. RUP, pioneered by Rational Software, has three most important features:

(1) Software development is driven by use cases.

(2) Software development focuses on architecture design (ArchitecturalDesign).

(3) Software development is an iterative process.

RUP consists of four phases, each of which is divided into several iterations, each with a core workflow.

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