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Re: [ddlm-group] Finalizing DDLm

Herbert: I think David was more concerned about the dictionary
structure rather than the datafile presentation, but you raise an
interesting point regarding the equivalence of one-row loops and a set
of key-value pairs.  Semantic information *is* lost by turning a
one-row loop into key-value pairs:  we lose the information that these
dataitems 'belong together', as the key-value pairs are semantically
on the same level as all the other datablock key-value pairs. This
information can, of course, be recovered by reference to a dictionary.

The practical effect of this semantic loss is that programmers will
not be able to count on the parser pre-packaging loops for them, and
will thus need to allow for reconstruction of loop datastructures when
performing per-loop operations (such as in dREL methods).   I don't
think this is a big problem, but it is an increase in complexity, and
I do not see what we gain by allowing such an equivalence.

On Fri, Mar 12, 2010 at 4:37 AM, Herbert J. Bernstein
<yaya@bernstein-plus-sons.com> wrote:
> I would favor treating a looped presentation of a single row of items as
> valid in all cases, and treating the presentation as individual tags
> and value as equally valid and equivalent.  I also like David's suggestion
> of allowing a individual tag and value to be distributed over a loop
> for the same category.  This would start to put us into a parallel position
> to the handling of XML attributes.

Regarding distributing individual tags and values over a loop, I think
the current DDLm approach of 'Set' and 'List' categories combined with
parent/child relationships is adequate for our needs.

>
> At 10:35 AM -0500 3/11/10, David Brown wrote:
>>Dear Colleagues,
>>
>>I assume that we are essentially finished in resolving syntax
>>problems, but in that discussion some items were identified as being
>>related to DDLm rather than syntax, so before we settle into serious
>>dictionary writing we need to understand the DDLm rules.
>>
>>One item that I believe was raised under this heading was whether,
>>if a loop contained a single set of items, it was necessary to
>>formally include this in a loop structure.  If this is deemed to be
>>necessary, then there has to be some way of identifying the items
>>that must appear in a loop.  The presence in the dictionary of a
>>_category_key.* item would seem to flag this, but it is applied at
>>the level of the category rather than at the level of an individual
>>item.  If the requirement that the loop structure must always be
>>used, then all the items in the category must be loopable, i.e., the
>>category cannot include items that would not normally be included in
>>the loop, items for example that apply equally to all the listed
>>items such as a scale factor that is the same for all the structure
>>factors in a loop.  This seems to be workable, but I am not sure how
>>the legacy CIFs would fit in, since categories may include some
>>listable item and some non-listable items, and I am sure the
>>listable items do not always appear in a loop if there is only one
>>set of such items reported in the CIF.
>>
>>Is this something that can be clarified fairly easily?  It has an
>>important bearing on how the CIF dictionaries are written.
>>
>>David
>>
>>Attachment converted: Macintosh HD:idbrown 55.vcf (TEXT/ttxt) (0046DFC7)
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>
>
> --
> =====================================================
>  Herbert J. Bernstein, Professor of Computer Science
>    Dowling College, Kramer Science Center, KSC 121
>         Idle Hour Blvd, Oakdale, NY, 11769
>
>                  +1-631-244-3035
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> =====================================================
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