Visual Modelling R J Walters

Introduction Motivation The Language The tools An example Conclusion

Issues in threaded and distributed systems Connecting the parts Getting the result to make sense

RaDraw A tool for generating RolEnact models

Background: RolEnact A tool for investigating the behaviour of Role based models First models built using “raw” Enact code Now has –simplified language –32 bit implementation

A RolEnact model running Separate (named) window for each instance of a Role First line inside window shows present state of Role List of possible actions Perform an action and all Roles re-evaluate their state

“Raw” RolEnact code class Control < Role. class Counter < Role. Control.addEvent('New_counter). Control.New_counterReady():= self.inState('initial). Control.New_counterDoit():= (self.setState('initial); self.Counter:= Counter.create(); self.Counter.Control:=self). Counter.addEvent('Enquire). Counter.EnquireReady():= self.inState('initial) and Account_System.exists('initial). Counter.EnquireDoit():= (self.setState('waiting ); aRole:=Account_System.choose('initial); aRole.setState('searching ); self.Account_System:=aRole; aRole.Counter:=self).

New RolEnact code Create Control.New_counter Me( initial -> initial= ) New Counter End Selection Counter.Enquire Me( initial -> waiting ) Account_System( initial -> searching ) End Better, but still “too hard” for target users

RaDraw A friendly front end Displays RE model as code or a diagram Can build and edit a model Calls RolEnact to run a model

But Diagram and code are not equivalent Difficulty with what the diagram means … I wanted to do something better

RDT Draw your processes (components) Draw how they are connected Run the model in the execution tool Use a model checker on it - SPIN * Limitations are accepted in exchange for ease of use

RDT: Processes Process has state Displayed as a picture Built using system of dialogue boxes 3 types of event –Receive –Send –Create

RDT: Events, Receive

RDT: Events, Send

RDT: Events, Create

An example process

RDT: Models Add instances of processes to your model Describe how these instances are (initially) connected

Models: Process Instances

Models: Connections

Example model

What next? Execute the model Use a model checker on it

Channels: Communication in RDT is based on that used in the pi-calculus Similar identity between values and channels RDT also permits asynchronous communication –Need channels in the execution tool

Executing the model Each Process instance has a window which shows: –Name and type –State –List of available actions –List of local channel names mapping these to instances of channels

Executing the model Each Channel (instance) has a window which shows: –Name –List of values held in the channel

The Execution tool

Conclusion Language, model construction tool, execution tool, translation tool Builds formal models using “informal” methods