Introduction to Time Graphs

Time graphs define the behavior of different objects over a time scale. It provides a visual representation of an object's state and interaction over time. It can be used to:

Time graph elements and connectors can be generated from the 'Timing' page of the Diagram Toolbox.

Example of a time graph:

Elements of a time graph

Icon	Element description	Description
	State lifeline	A state lifeline represents the state of an object over a period of time, representing discrete transitions between states based on changes on the y-axis
	Numerical lifeline	Numeric lifelines represent the state of an object over a period of time, and parallel lines along the x-axis represent a steady state.
	Message labels	Message labels are another way to represent messages between lifelines, which is useful for "collating" a time graph of messages that are scattered around.
	Message endpoints	The message endpoint represents the message: Terminates at an undefined point outside of a state or numeric lifeline and begins at a determined point within a lifeline An undefined point that originates outside a state or numeric lifeline and ends at a definite point within a lifeline
	Chart entry	Chart entry means message: Terminates at a defined point outside of a state or numeric lifeline, starting at a specified point within a lifeline Originates at a defined point outside of a state or numeric lifeline and terminates at an identification point within a lifeline

State lifeline

A lifeline is the path that an object travels over a period of time, as indicated by the x-axis. There are two types of lifelines: state lifelines (defined here) and numeric lifelines, both of which are used in time graphs.

State lifelines follow discrete transitions between states, which are defined along the y-axis of the timeline. Any transition has optional properties for time constraints, duration constraints, and observations. An example of a state lifeline is shown below:

In the example diagram above, the OK transition point has the following properties:

Transfer point attributes

A state lifeline consists of a set of transition points. Each transition point can be defined using the following attributes:

OMG UML Specification:

The OMG UML specification (UML Superstructure Specification, v2.1.1, p.518) states:

This is the state of a classifier or property, or some testable condition, such as a discrete, enumerable value.

It is also allowed that the state dimension is continuous and discrete. This is illustrative for scenarios where some entities experience continuous state changes, such as temperature or density.

Numerical lifeline

A lifeline is the path that an object travels over a period of time, represented by an x-axis. There are two types: numeric lifelines (defined here) and state lifelines, both of which are used in time graphs.

Numeric lifelines show the state of the lifeline in the graph, and parallel lines represent the steady state. The intersection between the lines indicates a shift or change in state.

Here's an example of a numeric lifeline:

In the example diagram, the 10ms transition point has the following properties:

The OMG UML specification (UML Superstructure Specification, v2.1.1, p.518) states:

Displays the value of the connectable element as a function of time. Values are explicitly represented as text. Cross-reflect events where the value changes.

Message labels

Message labels are an alternative way to represent messages between lifelines, and are useful for "collating" a time graph of messages scattered around. To indicate messages between lifelines, draw a connector from the source lifeline to the message label. Next, draw a connector from another message label to the target lifeline. Note that the label names must match to reflect that the message occurred between two message labels.

This diagram illustrates how to construct messages between lifelines using message labels.

OMG UML Specification (UML Superstructure Specification, v2. 1 。 1 ， p 。 518) states:

Labels are just symbolic shorthand to keep the chart out of clutter, many messages crisscrossing between lifelines that are far apart. Tags indicate that messages can be corrupted by the introduction of a tag with the same name.

Message endpoints

The message endpoint element defines the termination of a state or numeric lifeline in the time graph. It indicates the message:

•  Terminates at an undefined point outside of a state or numeric lifeline and starts at a marked point within the lifeline

•  Originates at an undefined point outside a state or numeric lifeline and ends at a definite point inside a lifeline

Chart entry

A chart entry is a simple, graphical way to indicate where a message can be transferred to or outside of an interactive fragment. A fragment may be required to receive or deliver a message; Internally, ordered messages reflect this need, indicating the entrance at the boundary of the fragment frame. Any external messages that are synchronized with this internal message must correspond appropriately. Portals can appear in interaction diagrams (sequence, time, communication, or interaction overview), interaction events, and combined fragments (to specify expressions).

Relationships with time graphs

Icon	Element name	Description
	Message	A message represents the flow of information or the transfer of control between elements

Message

Messages are communication links between lifelines in a time graph. In the case of Timeline, Message is a connection between two Timeline objects.

For example

Example: Create a time message

You can create a time message between two lifeline objects (status or value) on a time graph, each with an existing transition point.

Here's an example diagram of a configuration message:

Timing Message Attributes:

•  The source of the message can be freely moved along the source timeline; However, the target side (arrow) must be attached to a transfer.

•  If a new Message is created and it is not given a target Transfer, it will automatically find and attach to the most recent Transfer; If you move the target side, it will drag and drop the transfer.

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