XMILE

[Karim Chichakly]

I promised an update to the XMILE documents and here it is just in time to discuss at the ISDC conference. I have said many times that this is getting implemented in iThink and STELLA. After many delays, I can now honestly say we have started. We expect full level 1 support and partial level 2 support in our next release.

The discussions around XMILE often deteriorate into taking completely different tacks or starting over again or incorporating other paradigms into XMILE. I think the latter is great if we can do it, but not as a first step. The push for standards has been going on for at least 6 years and our users want it. Are we going to continue to delay this so long that we prove Len correct - that the vendors will never do this?

I am looking for constructive criticism about the basic language and the XML implementation. These documents are not complete; I needed about another week to wrap up my thoughts.

Note the macro language is now Turing-complete. The SMILE language is as well, although that is not completely defined yet in XMILE (an additional option is needed).

I also took a controversial tack and made MathML optional. I think it should be supported, but at the user's discretion, as it bloats the file and we have a clear syntax defined for SMILE equations. Open source parsers for the syntax can be made available in several languages, so why force the overhead of MathML in all cases?

I have also enclosed some examples.

Happy reading,

Karim

[Bill Rathborne]

I sure wish I had the smarts to contribute! Looking at the XML files is a real treat at least in the sense that a trained user has an understandable text file to assess and modify. At least my untrained eye sees it this way.

In addition to portability, is there any sense that this might aid in the introduction of modeling in the elementary and secondary school systems? As is well understood gaining "entry" and sustaining it has proven to be a daunting task.

Best of luck to all those involved in this endeavor. It looks critical to me! (said the blind man!)

Cheers,

Bill

[Bobby Powers]

This is really fantastic work. I've been looking for a while and haven't found anything close to as useful of a SD reference specification as Simile (I know there have been copies up for a while, but I had it in my head that it was something else...). I hear there was some discussion at Albuquerque about XMILE, any chance for a public account/recap of what was discussed or decided?

[Karim Chichakly]

Hi Bobby, thanks! It has taken a lot of hard work and I wish I could say it was finished. Representatives from a number of companies (isee systems, Ventana Systems, PowerSim Software, XJ Technologies, and Forio Business Simulations) met at the conference to discuss implementing this across a number of packages. We agreed to start with a slightly more modest version (simpler identifier rules and simpler macros) which I need to write up and post in the coming weeks. We also agreed to start generating simple XMILE files in our respective packages that we can pass around to flesh out inconsistencies in the spec. We hope to have some generated XMILE models sometime this fall. Bob Eberlein suggested we shoot for Halloween, October 31st, so that is the present target for the first most basic interoperability test.

After that test, there will still be a lot of work before this gets to the point of being a shipping feature in the various packages. We are all looking to add some level of support in upcoming releases.

[Magne Myrtveit]

Hello,

I have some modelling language/file format questions at the onset of the new year:

Does anyone know the current status of the SMILE language and its XML representation? (Refernces?)
Is there a separate forum or wiki covering this topic? Do some of the Vendors support reading/writing XMILE files?

A related question: Are the STELLA/iThink format, the binary Vensim file format, and Powersim's file format(s) made public or are they kept secret by the resoective vendors?

Best regards and Happy New Year,
Magne Myrtveit

[Karim Chichakly]

Hi Magne,

Bob Eberlein and I spent quite a bit of time refining the spec last fall. I have been remiss in not posting the new version, but I expected it to change further. It hasn't, so I will now post what we arrived at a year ago. [Unfortunately, the forum is not letting me post it.]

The spec is not yet complete, for example, level 3 is still not specified, but it is a starting point. There will be some changes over the next few months as we start to define and implement level 3.

isee systems has been adding level 1 and level 2 XMILE support to iThink/STELLA and will release it with version 10. Bob was working on the same for Vensim, but, as you probably know, he has just left Ventana. I do not want to speak for Ventana, but it is fairly certain support for XMILE in Vensim will be delayed.

Bob had talked about setting up a separate forum for this topic, but for now, this appears to be it.

The STELLA/iThink binary format is not public. I do not think I would call it a secret, but we do not have time to document it. There isn't really much internal documentation either - other than the code that reads and writes it.

Best regards,

Karim

[Thomas Fiddaman]

I don't know that Bob's departure implies a delay in SMILE/XMILE implementation, but it is fair to say that we haven't set a date for that functionality.

The Vensim binary format is also not public, nor formally secret. However, there's nothing in the binary format that isn't fully documented in the text .mdl format, so there's no real reason to want binary. Also, most of what's in a model can be extracted through the Vensim .dll.

[Karim Chichakly]

Tom, that is good news! Here are the specs I tried to post earlier (thank you, Bob!).

[Magne Myrtveit]

Many thanks to Karim and Tom for providing this information so quickly.

I can understand why the binary formats are not published. It is a lot of work to document such formats, and once a format is publiched, it is hard to change it without causing trouble for people relying on the format.

The text format of Vensim is great to have available. Is there something similar fot STELLA/iThink, or will XMILE be the format you will provide, Tom? Is the STELLA/iThink documentation available on-line somewhere, or does it require a licence to get one?

Best regards,
Magne

[Robert Eberlein]

If there is sufficient interest we can add a forum specific to model interchanges issues to the discussion boards. This could even be done as a Special Interest Group activity.

Perhaps this could be the Special Interest Group for Open Standards in System Dynamics. The mandate could be not only XMILE related things but also such things as diagrammatic conventions in stock and flow and causal loop diagrams. Many of these are common, but there are also stylistic choices that vary between people. The purpose would not be to say what is right, but to provide a common legend people could refer to.

If you are interested in contributing to such an endeavor reply on this thread.