REPLY Who wants to share models (SD6874)

[SDMAIL Bill Harris]

Posted by  Bill Harris <bill_harris at facilitatedsystems.com>

"SDMAIL Bill Braun" <bbraun at hlthsys.com> writes:
> Dividing a model into sectors as you suggest is viable. Is that the same 
> as co-constructing? Is such a thing possible given the complexities of 
> modeling, especially large projects? If there were a universally 
> recognized library of pieces and parts it might be. There are many good 
> examples of that also. I'm not sure of their universal acceptance as 
> building blocks (nor have I even thought about the desirability of such 
> a thing let alone the practicality).

Bill B.,

Before people get too far into the libraries idea, it might be worth
taking a look at the software engineering side of things.  Sure, there
are massive libraries in some cases (STL and GSL come to mind), but the
challenge with such libraries is the amount of information you need to
know and remember (or look up) in order to get work done.

One of the advantages of SD has been that the methodology is simple and
the focus stays on the problem.  Barry Richmond once opined here, IIRC,
that he got along just fine almost all of the time with combinations of
five or so standard structures.  The Molecules give more structure for
cases where it's advantageous, and the various books and texts give
examples of bigger structures for specific situations.

I conjecture that models any bigger than the molecules would likely be
big enough so that they are not much fun to copy manually, at least if
we consider them as productivity aids * (remember typing in programs for
Apple IIs or C-64s in the 1980s?), so libraries might then become
vendor-specific.  In the programming side, that seemed to provide
temptation for vendors to make "improvements" that contain features that
lock people into their solutions, which (I think) led to more emphasis
on things such as the STL.  

  * If we consider them as teaching tools, then I suspect people are
    better off studying existing models and building their own rather
    than thinking they should be memorizing these new standards.

If it's truly needed, a SML (Standard Model Library, to use an
overloaded acronym) could help, but, in that case, why not simply switch
to Goldsim (I think they're farther along in that direction)?  The
effort to create a cross-platform (OS X, Linux, Windows) set of
libraries callable from iThink, Vensim, and Powersim doesn't sound
trivial, and the effort to recall the API for each of the structures in
the library wouldn't be trivial, either.

"SDMAIL Bill Braun" <bbraun at hlthsys.com> writes:
> How a group might collaborate to write a paper is a good example. The 
> ability to track changes, have multiple versions, and compare documents. 
> I realize there is a magnitude of complexity well beyond the written 
> word involved, but it may still serve as an example.

If you're working with a text-based simulator (versions of Vensim are
likely the most popular, but MCSim, DYSMAP, and DYNAMO qualify), what
about using Google Docs, create the model in a document, work on it
together letting Google Docs manage the interaction, and save it as text
on anyone's computer who wants to run it?


"SDMAIL Kate Thompson" <k.thompson at edfac.usyd.edu.au> writes:
> I have to agree with Martin on this one. I use a combination of an 
> online chat environment and a wiki for my (masters level) students to 
> collaboratively build models. They have access to a shared whiteboard as 
> part of the chat environment so that they can synchronously work on 
> their causal loop diagrams with discussion, but they have to make 
> changes to their actual models separately, upload to the wiki, the rest 
> of the group has to download, open, and make appropriate changes etc. 
> What actually happens is that one or two students end up being the 
> "modellers" and upload screenshots instead of the actual models, the 
> rest of them comment on what they think should be changed... but it 

Hi Kate,

That sounds like more reason to have plain text as the interchange
format for models (yes, I have used *nix systems for quite a few years
and been infected with the *nix philosophy).  I haven't done exactly
what I'm suggesting, but I imagine that a bit of ingenuity and a bit of
effort would let you modularize one text-based model such that
individuals could work on their parts, they could upload them to a
server, and a script could build the resulting full model, ready to run.

With Vensim .mdl files, I suspect that the toughest problem would be the
part at the end that describes the layout of the sketch.  With Vensim
Professional or DSS, that's probably not an issue (unless you want to
see a pretty sketch), but it could be with less expensive versions.
There's something to try out.

With MCSim, the toughest problems are likely sorting equations (it
doesn't do that for you) if you divided the work by sector.  If you
divided by section of the model file, that's probably not a problem.

With text-based models, diff and patch might be a help, too.  If
everyone starts with the same current gold version, each person makes
their changes, and then each person runs diff to get a patch file.  Then
you just upload the patch files to the server.  Everyone grabs the patch
files and runs patch locally.  I'm not an expert there, and I know you
can get into trouble if there are too many overlapping patches, but, for
smaller groups without too much chaos, that might be the easiest way to
speed up what you're suggesting.

> could be better. What would be great would be an online resource that 
> allowed students to build the models synchronously (and writing all the 
> changes to a database so that we could "see" what they changed and 
> commented on would be helpful too).

What about tools such as Vyew, WebHuddle, Elluminate, WebEx, Live
Meeting, HP Virtual Rooms, Adobe Connect, ...?  That's the way I've done
it.  Perhaps your university even has a license for one of those (and
some have free versions).

Bill
- -- 
Bill Harris 
Posted by  Bill Harris <bill_harris at facilitatedsystems.com>
posting date  Mon, 07 Apr 2008 08:42:26 -0700