Design/CPN Survey Comments (May 1998)

Comments on Editor

``I also noticed binary incompatabilities between the Linux and Solaris versions which restricted model import/export (very important since you can edit on a small linux machine then export to a big solaris box for analysis).''

You are right, there are a few problems with moving diagrams between the Solaris and Linux platforms. It is described in our bug list. In the forthcoming release (v3.1) we have implemented a new diagram format which is textually based, a so called interchange format. This will solve the problem. The interchange format solves also the problem of moving diagrams between different kinds of tools.

``The editor is very good to work with, since it got all the necessary features that a graphic tool demands. It would be better if undo options are incuded for more operations.''

Currently it is only possible to undo alignment operations. Although full undo would be useful we presently have not planned to extend it, mostly because it is difficult to implement.

``Features to include stochastic event times should be made to be included in a more easier manner.''

We are currently spending some time on research in the performance modelling area. Some activities are directed towards making better library support for simulation with probability distribution functions and automatic collection of statistics. At the CPnets'98 workshop there will be a Design/CPN tutorial on this matter.

``I think that colors and predefined objects will be appreciated.''

So do we! Therefore we are currently implementing them on all UNIX platforms. (Mac already have support for colours.) We expect that colours will be available in version 3.2 which is planned to be released in the fall.

``In my opinion, the editor is very poor for large models. There are lot of little bugs but it is critical for such models.''

You are probably right. However, if you do not tell us more specifically which bugs you frequently experience then we will never know. Bug reports can be submitted by means of an online fill-out form. Reproducable bugs are most likely to get fixed.

``A grid for the Editor to align the Nets.''

Layout of diagrams is dominated by the features of the alignment facilities in the tool. The Align-menu has a lot of general alignment features, where grid in principle can be imitated. It is not clear how grid and align could co-exist. We have not worked on this and is open for discussion.

Comments on Syntax Check

``Better error messages!''

The error messages are taken directly from the SML compiler which is used to parse a CPN model. They are not always easy to understand as they require familiarity with SML. Our best advice is to be patient and get experience. If you are stuck you can always send the diagram to our technical support staff.

Comments on Simulator

``My biggest problem with the tool is the simulation time. I started working with Design/CPN but the enormous simulation time made me change to another software tool. I was working with Design/CPN for four months, and when I finished one model of an Interconnection Network, the simulation time was more than two weeks. The software tool that I have actually, reduces the simulation time to a few hours. Neverthless, my new software tool has not graphical editor and neither formal methods, so in case that the simulation time of Design/CPN would be improved I would work with it again.''

We have experienced that simulation of models with large markings (a place with thousands of different tokens) may result in poor performance of the simulator. The present simulator was not really designed with this issue in mind. A new version of the simulator has been redesigning from scratch with optimised datastructures and algorithms for large models/markings. Our plan is to release Design/CPN 4.0 containing the new optimised simulator in the beginning of 1999.

``Some more detailed error messages from the simulator would be great. I produced automatic code and i always get an exception, but i can not get any information, where the code is located in the model. Maybe a debug mode would be fine.''

We are aware of the exception problem and have therefore made some improvements in the forthcoming release (v3.1).

``Impossibility of stopping simulation in the middle of a long step.''

In the current version of Design/CPN it is not possible to stop automatic simulation (only interactive). During automatic simulation the ML-engine has complete control and is therefore difficult to stop in a consistent state. We are working on a solution to this problem.

Comments on Occurrence Graph Tool

``The OG tool presents several problems. Getting to know how to use ML for querying is difficult. More graphical interfaces to a wider range of queries would be useful.''

Many resources are currently being put into this part of the tool. It is in general a very active research area. SML novices will have difficulties with queries, but once mastered it is a very powerful means of making customised analysis.

``The OEOS capability of the OG tool could be simpler (automated). This would increase usability and reduce the chance of the user creating an erroneous OEOS spec.''

The OEOS tool is our latest extension of the occurrence graph tool. The CPN-group at DAIMI is presently focused in this research area. There is room for many improvements which we plan to make contribution to.

``I'd like to see compatible as well as consistent support for OEOS.''

So do we. One of our Ph.D. students is involved with making OEOS more user-friendly. Semi-automatic support for compatibility and consistency checks is being considered.

``There are still a lot of research work to do to get a practical occurrence graph tool. It is not the problem of Design/CPN, but a challenge to Petri Net researchers.''

We agree!

Other Comments

``Windows 95 / Windows NT based system.''

We often get this request. Our problem is very simply: lack of resources. Presently we do not have the time and funds to make a port to MS Windows. (If you do, we would like to hear from you.) Thus we currently only expand to new platforms which are UNIX-like, such as HP.

``The tools look pretty good, but I'm still a bit of a novice at the tool and the learning curve is a bit steep. I think I just need to take the time (which means get the time to work on the "right" part of my job).''

Design/CPN has a large set of features which will take time to master. The online tutorial and manuals may be what you need to get started.

``I have always received excellent technical support when I needed it.''

Thank you. Maybe there is no such thing as free lunch, but we do offer free technical support. Do not forget that we also offer a Design/CPN mailing list. Some of the problems sent to technical support would be of greater benefit for other users if posted on the mailing list.

``Of course, Design/CPN is not a perfect tool, but it is a very usefull one. I hope my comments will help you to improve it.''

We agree. If we do not know about your problems we cannot fix them.

``It would be useful to have more complex programming examples in CPN ML manual. In addition, more online diagrams could be provided.''

As you know there are a number of toy examples available online. However, we do not really have any large realistic examples online. We would be very interested in hearing from you should you have a nice CPN model, small or large. See "How to Publish Your Own Design/CPN Examples". Such examples would be of great benefit of other Design/CPN users.