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Re: [ddlm-group] Finalizing DDLm

1.  Existing DDL2 style dictionaries have many looped categories with 
subcategories.

2.  I do not understand why there is any special need to forbid the
presentation of a single row list category as separate tags and
values, nor why there is any special need to forbid the presentation
of an unlooped catagory as a single row loop.  Any necessary coercion
is easily done in either case, and deserves at most a warning, if even
that.


=====================================================
  Herbert J. Bernstein, Professor of Computer Science
    Dowling College, Kramer Science Center, KSC 121
         Idle Hour Blvd, Oakdale, NY, 11769

                  +1-631-244-3035
                  [email protected]
=====================================================

On Tue, 30 Mar 2010, David Brown wrote:

> James seems to have summarized matters pretty well.� The implication is that
> a list category must be the end of the line - it cannot have a subcategory.�
> My real questions was whether a list category must explicitly included as a
> loop, or whether the loop structure is unnecessary if it only contained a
> single row.� It is easy enough to be safe by always inculding the loop, and
> I will probably arrange to do this in the dictionaries.� There are likely to
> be several places with single fow loops appear, e.g., in examples or
> aliases.
> 
> David
> 
> 
> 
> James Hester wrote:
>       Thanks Nick for clarifying this.� We then return to David's
>       question.� If we assume that a 'Set' category cannot be a child
>       of a 'List' category (I hope this is written down somewhere if
>       it is the case) then my originally proposed solution would be
>       impossible.� Therefore, what David should do is to put the
>       invariant items into a *parent* 'Set' category and state that
>       the child 'List' category.� That would solve the immediate issue
>       of separating out looped and unlooped datanames.� If some
>       convenience is desired for dREL processing, the child 'List'
>       category could be made joinable to that parent category, thereby
>       making both invariant and looped items available in shorthand
>       form by looping over the parent category.� Of course, even if
>       the child 'List' category is not explicitly joined to the parent
>       'Set' category, the parent category can be explicitly referenced
>       in any dREL method using the full dataname.
>
>       Nick may wish to confirm that I have correctly understood the
>       proposed behaviour of DDLm.
>
>       James.
>
>       On Thu, Mar 25, 2010 at 3:18 PM, Nick Spadaccini
>       <[email protected]> wrote:
>             I have not had any time to respond to David?s
>             original email or the
>             subsequent discussions. However I have discussed it
>             with Syd.
>
>             DDLm defines loopable categories strictly and
>             sub-categories of those have
>             strictly enforced outer joins (given we have ONLY
>             considered sub-categories
>             that are List). This is how we overcome the split
>             versus non-split versions
>             of atom_site and atom_site_aniso loops. List is
>             strictly looped, Set is
>             strictly non-looped - contrary to your reading, and
>             possibly Syd?s original
>             text. He has since re-read what he wrote and
>             clarified the ambiguity. I will
>             send you that re-write shortly.
>
>             We had not considered a SET category being a
>             sub-category of a List
>             category, but if it is allowed then it would not be
>             an outer-join as you
>             suggested in your previous contribution but a
>             relational Cartesian product
>             (which is very different).
>
>             The DDLm specification has that List category data
>             MUST appear in a loop
>             (irrespective of how many rows there are), and SET
>             categories are strictly
>             singular (non-looped data). The formal specification
>             will formally remain
>             that way.
>
>             HOWEVER the IUCr is free to ?extend? the
>             specification of the DDLm for its
>             own internal and private use, so long as you
>             appreciate that the FORMAL
>             published specification of what Syd and I have
>             created can?t include it.
>
>             You might explain as to why you feel you have
>             trouble with
>
>             loop_
>             �_atom_site.label
>             �_atom_site.frac_x
>             �_atom_site.frac_y
>             �_atom_site.frac_z
>             �Cu 0 0 0
>
>             And yet
>
>             �_atom_site.label �Cu
>             �_atom_site.frac_x �0.
>             �_atom_site.frac_y �0.
>             �_atom_site.frac_z �0.
>
>             Is so much more obvious? Given that people
>             understand what the loop is, I
>             can't see what they would gain from the unrolled
>             version (apart from
>             confusion). The real danger is those less
>             experienced who DON'T read a
>             dictionary and read the latter form may be
>             encouraged to replicate it when
>             there is more that 1 atom (thus corrupting the CIF
>             structure).
>
>             However these are just personal observations, and if
>             the IUCr wants to
>             qualify the use of DDLm with its own tweaks there is
>             nothing stopping them
>             from doing so.
> 
> 
>
>             >>>>
>             >>>> 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)
>             >>>>>
>             _______________________________________________
>             >>>>> ddlm-group mailing list
>             >>>>> [email protected]
>             >>>>>
>             http://scripts.iucr.org/mailman/listinfo/ddlm-group
>             >>>>
>             >>>>
>             >>>> --
>             >>>>
>             =====================================================
>             >>>> �Herbert J. Bernstein, Professor of Computer
>             Science
>             >>>> � �Dowling College, Kramer Science Center, KSC
>             121
>             >>>> � � � � Idle Hour Blvd, Oakdale, NY, 11769
>             >>>>
>             >>>> � � � � � � � � �+1-631-244-3035
>             >>>> � � � � � � � � �[email protected]
>             >>>>
>             =====================================================
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>             >>>>
>             http://scripts.iucr.org/mailman/listinfo/ddlm-group
>             >>>>
>             >>>
>             >>>
>             >>>
>             >>> --
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>             >>> F +61 (02) 9717 3145
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>             >>
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>             >>
>             >
>             >
> 
> cheers
> 
> Nick
> 
> --------------------------------
> Associate Professor N. Spadaccini, PhD
> School of Computer Science & Software Engineering
> 
> The University of Western Australia � �t: +61 (0)8 6488 3452
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> 
> 
> 
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> 
> 
> --
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>
>     ____________________________________________________________________
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>
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