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Introduction to UML timing diagrams

UML Sequence Diagrams are interaction diagrams that emphasize the chronological order of messages. UML timing diagrams describe class-to-class interactions in a class system, modeling these interactions as message exchanges. A UML sequence diagram is a model that describes how groups of objects collaborate on certain behaviors over time.

UML sequence diagram is an interaction diagram that emphasizes the sequence of messages. It consists of Actor, Object, Message, Lifeline, and Focus of Control. In UML, an object is represented as a rectangle, where the object name is underlined; messages are represented by marked arrows in UML sequence diagrams; lifelines are represented by dashed lines, and control focus is represented by thin rectangles.

UML time diagrams represent interactions as a two-dimensional diagram with a vertical Timeline and time running down vertical lines. The horizontal axis represents the generic role of each individual object in the collaboration. The activities of a generic role are represented by lifelines. When an object exists, the lifeline is represented by a vertical dashed line, and when an object's process is active, the lifeline is a two-channel. Messages are represented by arrows from the lifeline of one object to the lifeline of another, arranged in chronological order from top to bottom in the diagram.

General Guidelines for Designing UML Sequence Diagrams

◆ Try to keep messages in order from left to right

Stratification of classifiers

Avoid modeling object Destruction

◆ Principles of classifiers

◆ Message principles

◆ Create objects directly

◆ Description type for parameter placeholder

◆ The message implementation of the class is static operation

◆ Principles of return value

Do not model return values when they are obvious. Return values are displayed using dashed arrows marked with return values. Return values are optional.

◆ Indicate type for return value placeholder

◆ Clearly indicate actual values for simple values

Use of UML Time Diagrams

Describe the overall sequence of control flows when there are multiple short methods between different classes.

Displays concurrent processes and activations.

Displays time series that are difficult to describe in collaboration diagrams.

Displays generic forms that involve class interactions and are independent of objects.

UML Sequence Diagram Components

Dynamic model describes the behavior of the system with time, which is described by the instantaneous value of the system extracted from the static view. In UML, dynamic model mainly establishes the interaction diagram and behavior diagram of the system.

Interaction diagrams include UML sequence diagrams and collaboration diagrams, while behavior diagrams include state diagrams and activity diagrams

UML Sequence Diagrams are used to show relationships between objects, emphasize the chronological order of messages between objects, and show interactions between objects.

UML sequence diagrams include the following elements: class roles, lifelines, activation periods, and messages

1, ClassRole

Class roles represent the roles that objects in UML sequence diagrams play in interactions, and are located at the top of UML sequence diagrams and objects represent class roles. Class roles generally represent actual objects

2. Lifeline

Lifelines represent the existence of objects in UML timing diagrams over a period of time. UML timing diagrams have a vertical dashed line at the center of each object and bottom, which is the lifeline of the object, and messages between objects exist between the two dashed lines.

3, activation period

The activation period represents the period during which an object in a UML sequence diagram performs an operation, and the narrow rectangle on each lifeline in a UML sequence diagram represents the active period. It can be understood as a pair of curly braces "{}" in C language semantics

4. Message

Messages are classes that define the information exchanged in interactions and collaborations, and are used to model what is communicated between entities, and information is used to transfer information between entities. Allowing entities to request additional services, class roles communicate by sending and receiving messages

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