UL⁺⁺ is an object oriented language to model real time system with timed automata. In our model, we use processes which have states. To model a system in UL⁺⁺ , one has to derive the primitives classes ConcurrentProcess, Process and SuperState. The idea is as following :

• a system is made of processes, which can be grouped in concurrent processes. When the user wants to simulate and verify his system, then he has to instanciate one object, which is a process or a concurrent process.
• inside a process one puts states and superstate. Superstates are sets of states and superststates as well

Then, as we use objects, we need to connect them together and we need to instanciate them. The scope of variables is always local and private, so that we use a data interface to instanciate the composite objects, which is a simplified version of constructors. To connect the composite objects (how to make a transition to a superstate for example), we use control interfaces which are mainly entries and exits on superstates.

Here is how it looks like :

The principle is to give interfaces to independant objects and them to develop them and connect them in a modular way.

Composition rules

We summarize and complete what we have said above in the following table :
 

class	initial state	entries/exits	State objects	Process objects
ConcurrentProcess				yes
Process	yes		yes
SuperState		yes	yes

Then we have rules for the data as well, saying what kind of data is allowed in which class :
 

class	clock	channel	static data object
ConcurrentProcess	yes	yes	yes
Process	yes		yes
SuperState			yes

A static data object is one of : Integer, BoundedInteger, Boolean, Array.
In the data interface (which appears in VisualUL) the user will find int which is an integer constant, a parameter to initialize the classes.

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