Simple Clock Modeling with SysML

It has been a while since I posted my previous article on this blog, because I was busy in making MagicDraw SysML supports for the new OMG SysML v1.3 Specification [1]. Couple weeks ago, I was asked by a customer about how to model a clock which counts every second with SysML. I created the simple clock model for answering. I also posted it to the SysMLForum and found that some people are interested in my clock model. So, I wrote this article to explain about the clock model and show how to model the system operating by a time trigger.

Start from defining the clock with a SysML block. The clock block contains only a value property t. This value property represents time in second. Thus, a value type Second must be defined for typing the value property as in Figure 1.

Figure 1 - SysML Block Definition Diagram of Clock Model

Next, SysML State Machine will be created to describe the behavior of the clock block. Here, the clock state-machine was designed to have only one state run as shown in Figure 2. It has a transition to itself triggered by a time event trigger with when attribute is set to 1,000 millisecond. So, the run state will be triggered every second (1,000 millisecond).

Figure 2 - SysML State-Machine Diagram of Clock Model

At the entry and the exit of the run state, you can specify the Behavior which will be performed when the state is entered and exited respectively. In this model, count activity (Figure 3) has been specified to be invoked at the exit of run state.

Figure 3 - SysML Activity Diagram of count activity

The count activity composes of the following actions:

1. ReadSelf action, is the action that returns the object of the current context. In this model, the token that flows through the result pin is the object of clock.
2. ReadStructuralFeature action, this action reads the value of the specified structural feature from the object (input) pin. Here, the specified structural feature is the value property t. So, the token that flows through the result pin of the action is the value of value property t.
3. CallBehavior action, is the action that calls to the opaque behavior IncreaseTimeOneSecond, shown in Figure 1. This opaque behavior has two parameters, tin (input) and tout (return), where: tout = tin + 1
4. AddStructuralFeatureValue action which is the action for setting the value to the specified structural feature of the object (object pin). In this model, the new value of value property t should replace the previous one. So, the attribute Is Replace All will be true.

(You can get more information about these actions in UML v2.4.1 Superstructure Specification [2])
The count activity will be performed every second when run state is triggered. So, the value of value property t will increase by 1 every second.

The simulation tool can be used to ensure that the clock model can work correctly. Here, I uses Cameo Simulation Toolkit, which can simulate the UML Activity and State-Machine model according to the fUML and SCXML specifications, as shown in the following video.

You can see that, the value of value property t will be increased by 1 every second when the model was simulated with full animation speed.

I hope this model can help at least someone to gain more understanding in using SysML for modeling time dependence system ;)

References:
[1] "OMG Systems Modeling Language (OMG SysML™) version 1.3" [Electronic]
[2] "OMG Unified Modeling Language™  (OMG UML), Superstructure version 2.4.1" [Electronic]

Kritsana Uttamang, PhD.

Analyst Manager / SysML Domain Expert
No Magic Inc.