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Re: [ddlm-group] A modest addition to the DDLm spec. .




On 1/10/10 10:54 AM, "Herbert J. Bernstein" <yaya@bernstein-plus-sons.com>
wrote:

> Dear Nic,
> 
>    If the spec is quoted string literal + quoted string litera;,
> +4 is no problem, it is just +4.

Unfortunately this means that a + can't be a legitimate unquoted string in
the presence of quoted strings, but can be if NOT in the presence of quoted
strings. This surely has to be confusing. Example

loop_

atom_site.id 
atom_site.charge_sign
atom_site.atom_type

"C123" + "C"

would return C123C plus an error for the missing data values for the last
two items.

At a lexical level 

"C123" + "C" is different to "C123" + C and different to C123 + C.

Since people use quoted and unquoted strings interchangeably I fear this
will give rise to ambiguity. Of course if you do away completely with
unquoted strings (I have argued this) the problem disappears. If all strings
have to be quoted then the symbol + will have a completely unique
interpretation.

> "breaking the underlying structure of a
> tag-value construct in the original STAR/CIF" is no more done
> by this extension than it was by the bracketed constructs.

This is a little disingenuous. The bracketed constructs were extensions to
make the representation more powerful. It actually didn't break the
underlying structure, since [string] was already allowed in the syntax. It
merely made the interpretation of the contents more in line with
expectation. The PDB had littered its data with [1,2,3] (no spaces) as
unquoted strings expressly representing lists. We just formalised it.

However 

single tag - single value is the definition of the STAR/CIF syntax. The new
formalism does break that.

But this is all moot. CIF2 is developing in a very different direction to
STAR and is no longer a subset. It is in some ways and an extension in many
others. DDLm can be extended to incorporate some of the changes to
definition language, but there are syntax variations that cannot. The same
with dREL where quite different language extensions need to be incorporated.

CIF2 is developing its very own syntactic definitions, its own DDL and
supporting scripting language, all of which can be based on STAR, DDLm and
dREL, yet very different.

The DDLm and dREL syntax and examples Syd and I issued for consideration
provides a good basis for this group to move forward. I am under pressure
from Syd to finalise the STAR, DDLm and dREL we implemented in to journal
papers - which I will do. I am under more pressure from my Faculty in
different directions. Time is short and my contribution to CIF2 discussions
is at best minimal, and of late non-existent. Good luck with these
developments and I hope to see applications in the near future that exploit
its possibilities.

cheers

Nick

--------------------------------
Associate Professor N. Spadaccini, PhD
School of Computer Science & Software Engineering

The University of Western Australia    t: +61 (0)8 6488 3452
35 Stirling Highway                    f: +61 (0)8 6488 1089
CRAWLEY, Perth,  WA  6009 AUSTRALIA   w3: www.csse.uwa.edu.au/~nick
MBDP  M002

CRICOS Provider Code: 00126G

e: Nick.Spadaccini@uwa.edu.au




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