RE: Re: dynamics: comment about MBdyn...

On Tue, 15 Jul 2003, Tiller, Michael (M.M.) wrote:

[...]
> > > The key thing is that "Syntax is not semantics".  Don't get me
> > > wrong, XML is a very nice technology and I use it every 
> > chance I get.  But
> > > it only covers the *SYNTAX*.  Modelica is much more than 
> > that.  Only a small
> > > part of the specification covers syntax.  
> > 
> > INdeed, and that's what the Schema's (formerly DTDs) are for: they
> > attach information about what is _meant_ with the parsed symbols.
> > So, I think Modelica would now talk about its XML and Schema
> > standards, instead of about its file format.
> 
> Not quite...schemas and DTDs only cover the structure of the file.
> They describe the grammar (what elements can appear nested what
> other elements, what attributes are associated with what nodes,
> etc).  They still don't cover meaning.
Of course they do! Look at a simple example, DocBook: when you use a
<section> ... </section> tag, you attach _meaning_ to the enclosed
block, and this meaning is, for example, used to determine what
typographical form to use when producing the DocBook layout.

When you encode a <rigidbody>...</rigidbody> block, you immediately
know the constitutive relationships, the relevant parameters, etc.
This is a lot of _knowledge_, hence semantics.

Herman

-- 
  K.U.Leuven, Mechanical Engineering, Robotics Research Group
<http://people.mech.kuleuven.ac.be/~bruyninc> Tel: +32 16 322480