[cddlm] CDL specification

[Stuart Schaefer]

Paul,

I had promised to Dejan I would respond to your earlier comment, but I
will try to respond here as the thread has continued in the same vein.

1) Semantics.  A bit of both sides of the argument.  The CDL language
draws its main semantic definitions from the SmartFrog project.
SmartFrog has fairly well defined semantics.  The CDL must define its
operational terms in some way.  It can do so using BNF, UML, XML or
whatever, as long as it has made clear how it is to be used.  If you
look at a project like RDF, the RDF semantics primer was just released,
years after the definition of the language specification.  Many people
have done great injustice to RDF in using it in bizarre and incompatible
ways.

The other side of the argument.  If the CDL has not disambiguated
important or edge scenarios, the likelihood of what you have proposed is
very high.  Reading others code won't solve the problem, as different
implementations may solve the situation differently.  A language must be
clear about what is and is not strictly enforced.

In reference to your example, I posed that exact question to Jun, the
author of the CDL specification some months ago and will ensure that it
is properly dealt with in the final release of the CDL spec.  The
component model relies on preservation of lexical order.  SmartFrog did
not have this limitation, as its templating language was much more
freely expressed.  There may be other semantics that are undefined or
not clearly defined.  I am not sure.  Do you have any other examples?

2) Languages like system configuration grammars are hard for people to
write.  People don't think this way.  Tooling is typically very
important for the successful implementation of any system.  Vanish from
HP was very helpful in showing the BPEL example.  BPEL is a very rich
language, but almost impossible to write by hand due to its complexity.
However, it is very clear how to create a tool that can write
well-formed BPEL, and many vendors and independents have done just that.

The purpose of CDL is to allow many contributors to a system definition.
I am not sure that people will directly author CDL.  On my side, we are
implementing higher level tooling that can use CIM and CMDBs to derive a
well-formed description, then parse down to CDL.  It works quite nice.

If you look at a language like DCML, it is written using RDF triples to
use an ontology of system descriptions.  Is that easier?

3) It would be helpful for me to understand what you consider research
features.  Working Groups don't do research.  We write specs based on
experience and implementations.

Regards,

Stuart

-----Original Message-----
From: Paul Anderson [mailto:dcspaul at inf.ed.ac.uk] 
Sent: Thursday, February 24, 2005 2:42 AM
To: Milojicic, Dejan S
Cc: Paul Anderson; cddlm-wg at ggf.org
Subject: Re: [cddlm] CDL specification 


>Hi Paul,
>
>I really appreciate your efforts in maintaining this discussion, it
>brings a lot of value to the whole process! We have discussed your
>comments in the regular meeting this morning. You may hear from others,
>but here is my perspective. .........

Many thanks for the response Dejan. This is pretty much what I had
expected - I do understand the pragmatic reasons behind these
decisions, but perhaps I can just summarise my concerns ..

1) If people are expected to make independent implementations of a
   langauge, they are much more likely to work correctly if the
   the language is defined by a written semantics, rather then by
   a reference implementation where people have to guess the
   significant parts of the semantics by reading someone else's
   code (for example, "does the order of these elements matter"?)

2) Certainly in the system config area, people at many different
   levels of skills will be expected to make contributions to an
   overall configuration, and we have identified the difficulty of
   learning to use the language as a major barrier to the uptake.
   Misconfiguration due to language confusion is also a major
   source of configuration errors. Hand-writing CDL is going to
   be significantly more difficult than the languages that we
   have considered previously.

I would like to have seem a simpler language which standardised on
the well-accepted basics, and left out (or made optional) the more
"research"-oriented" features which could be layered on top later.

I'll definitely keep you in touch about the workshop outcome, and
I'll probably have more questions before then ... :-)

Many thanks

	Paul