Mobile units, sensors or computers linked in a network. Everybody has a need for communication, a need that the research group Modelling and Validation of Distributed Systems has specialised in addressing.

”You know that you have a distributed system when a breakdown in a computer that you have never heard of prevents you from doing your job.”

The quotation from the American Professor of Computer Science Leslie Lamport nicely expounds what the research group Modelling and Validation of Distributed Systems is all about.

A more precise definition of distributed systems is hardware or software components located on network-linked computers that communicate and coordinate their actions exclusively by sending messages to each other. For example, this can be a sensor network or infrastructure such as the one that forms the basis for the Internet.

The research group is working specifically on developing languages that can be used to create models of distributed systems. The models can then be used to analyse systems before they are put into operation so it can be seen whether they do what they are supposed to with regards to functionality and efficiency.

Now with colours
The group is best known for the development of the software packages Design/CPN and CPN Tools, which are used to simulate distributed networks and most recently ASAP, which is used to verify the models that are created using CPN tools.

CPN stands for Coloured Petri Nets; a Petri Net is a graphic and mathematic modelling language, named after the German researcher Carl Adam Petri, who presented the Petri Net language in his PhD thesis in 1962. The research group’s (or more precisely: The group’s present leader, Kurt Jensen’s) contribution was initially to improve the language to become a so-called ‘high-level Petri Net language’ and called it ‘Coloured’, even though it does not actually have anything to do with colours.

”We have for many  years developed computer tools that support coloured Petri Nets in practice. They mean that the models that are created in the coloured Petri Net can be both constructed and analysed. Therefore CPN Tools has some similarity to a combined CAD and simulator tool”, explains Assoc. Prof. and PhD Lars Michael Kristensen from the research group.

CPN Tools is currently distributed free of charge to 7,000 licence holders in over 100 countries and has been in use since 2002. In addition, the group has used it in a large number of industrial collaborative projects with companies including Ericsson, Nokia and the Australian military.

The group is continuing to work on the development of Petri Net software so that it can automatically take the next step and contribute more directly to the implementation of the software for which it is a model.

”We can save time and money on this if we can get it to work. We had a meeting in France in August with Texas Instruments, who are showing an interest in our approach, so at the moment we have a small pilot project running in order to get to know each other”, states Lars Michael Kristensen.

From node to node
Whilst modelling and validation of distributed systems is what the group is best known for, the hottest topic that it is currently researching is the development of protocols for mobile ad hoc networks.

It is based on the development of communication protocols and software that can be used in network of mobile nodes (that is units in a network, e.g. laptops, telephones or sensors), which can exchange data via the network that they themselves form – and therefore not via the Intranet or Internet.

”We are working with communication networks where not all of the nodes are able to reach each other, but where individual nodes can with the aid of software come into contact with the nodes furthest away via the nodes that are located between them. For example, this can be used in mobile units in the military, where you drive around in an area without infrastructure, or in sensors in agriculture or industry”, says Lars Michael Kristensen.

In the development of ad hoc network technology CPN technology is naturally used to design and verify the protocols for the software.

The research group Modelling & Validation of Distributed Systems consists of three permanent members of staff: Professor Kurt Jensen, Reader Søren Christensen and Lars Michael Kristensen. There are also two post doctorates, four PhD students, a student programmer and a number of thesis students.