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Re: [ddlm-group] Objectives of CIF2 syntax discussion. .. .. .

I'm trying to get a grip on what problem the tag_style proposal
solves.  I'll just emphasise at the outset in case there are any
misconceptions that it is incorrect to suppose that the dREL method
knows or needs to know anything about the particular syntax in which
an input or output value is expressed; dREL is concerned purely with
describing relationships.

Here are the two scenarios that I think are being discussed under the
rubric of DDLm compatibility with CIF1:

Scenario 1: given a DDLm dictionary, a program wishes to generate and
(validate/insert) the value for some given CIF1 dataname in a CIF1
datafile, using other CIF1 tags found in that datafile.  We are all
agreed (I think) that locating the relevant DDLm dictionary entries
for a CIF1 dataname is a simple and well-defined task.  The formatting
of the eventual output value of the DDLm method is also not in the
purvey of the dictionary, but rather of the application that is using
the dictionary.  The particular CIF1 tag to put in the datafile is
also not an issue, as that was given at the beginning.  So the
tag_style proposal is not relevant here.

Scenario 2: given a CIF2 datafile, a DDLm application wishes to
produce an equivalent CIF1 datafile.  For many of the CIF2 datanames
found in the CIF2 datafile, there are multiple possible datanames
listed as aliases.  How is the application to ensure that it writes a
set of datanames from DDL1 dictionaries only or DDL2 dictionaries
only?  The simple solution alluded to by John B would be to do as
follows: for each dictionary URI mentioned in the alias list, use the
IUCr CIF dictionary register (and/or other canonical sources) to
determine the DDL version of that dictionary.  DDL conformance is a
standard entry in the dictionary register.  The latest dictionary
version as given in the dictionary register could be selected where
multiple versions are presented (URL for the register is

Of course, any program wanting to do such conversions efficiently
would pregenerate a DDL version - dictionary table once and refer to
that.  I therefore see no use, either in terms of efficiency or new
functionality, for the tag_style attribute.

Please advise if I have misunderstood the problem.

On Thu, Jan 20, 2011 at 11:20 AM, Herbert J. Bernstein
<yaya@bernstein-plus-sons.com> wrote:
> No, a tag style is simply supposed to identify a grouping of alias
> tag choices that belong together, so you can decide to put out
> those particular versions of tags.  It is just a text string,
> just like a alternate conformer identifier.
> The same tag name could be marked with a many tag styles as
> you choose.  It is just text.  But you could not give multiple
> aliases for the same DDLm tag for the same tag style when allowing
> DDLm missing value generation or you would not know which version to put
> out, and for validation, there is no reason not to use different
> styles for the different alternatives.
> The way I will write the extraction algorithm, if you choose
> a tag style, you will get the DDLm name for the tags that don't
> have an alias for the chosen style, but the tag alias given for the
> specified style is there is one.  That way a dictionary that is
> intended to support DDL1, DDL2 and DDLm for which the DDLm
> tags happen to be primarily consistent with DDL2 conventions,
> then for the tags that conform to DDL2 conventions, you will
> not need a DDL2 style alias, just a DDL1 style alias.  You will
> only need both a DDL1 style alias and a DDL2 style alias for
> a tag for which the DDLm tag is different from both, e.g.
> for _diffrn_standards_decay_% (DDL1), _diffrn_standards.decay_%
> (DDL2) and _diffrn_standards_decay_percent (DDLm).  When you
> want DDLm output and validation, you don't specify a style at all.
> This will be very nice to allow an automatic cleanup for dictionaries
> using a prefix, say pdbx, for tags that later get promoted to
> to not need a prefix.
> Regards,
>   Herbert
> =====================================================
>  Herbert J. Bernstein, Professor of Computer Science
>    Dowling College, Kramer Science Center, KSC 121
>         Idle Hour Blvd, Oakdale, NY, 11769
>                  +1-631-244-3035
>                  yaya@dowling.edu
> =====================================================
> On Wed, 19 Jan 2011, Bollinger, John C wrote:
>> On Wednesday, January 19, 2011 3:47 PM, Herbert J. Bernstein wrote:
>>>   The definition_id most certainly does not exhibit the tag
>>> style.  For example, there is no way to distinguish DDLm
>>> tag style from DDL2 or DDL2 tag style from context.  That
>>> is intentionally inherent in the design of DDLm.
>> Then I'm afraid I don't quite comprehend the meaning of "tag style".  I
>> would like to do, so that I can form a well-founded opinion about it.
>> As I thought I had understood the idea, the tag style is proposed to
>> identify the set of DDL conventions with which the given alias complies.
>> If that were indeed what it was intended to mean, however, then (1) as
>> you observe, some names would comply with more than one set of
>> conventions, but also (2) a set of candidate tag styles, at least, could
>> be generated could be computed for any alias name.
>> What would be the significance of marking an alias that conforms with
>> both DDL2 and DDLm conventions with tag style DDL2?
>> Might it ever be needful or useful to mark the same alias with more than
>> one tag style?
>>>   As for defining a hypothetical URI, that can break,
>>> or each least time-out programs trying to get additional
>>> information about an aliased tag from that URI.  URIs
>>> should be for things that really exist on the web,
>>> not a substitute for a tag that really defines something
>>> different, in this case the style of tags.
>> I don't think the issue is nearly so clear cut.  I would hold, for example, that the primary purpose of a URI is to *identify* a resource.  That's what the "I" stands for, as I'm sure you're aware.  RFC 3986 (Uniform Resource Identifier (URI): General Syntax) explicitly provides that a URI may identify an abstract resource.  RFC 2396 (now obsoleted by 3986) says the same.  Although many URIs fulfill their purpose by serving as resolvable web addresses, some, even among those formatted as URLs, do not.  Examples of the latter abound in various XML communities.
>> Personally, however, I think a bit more like you do: a URL ought to refer to a retrievable resource on the web.  For an abstract or virtual resource, therefore, I prefer to use a URN.  For something like your virtual DDL1 imgCIF dictionary, I might choose something like urn:x-imgCIF:DDL1.  If a URN were used, then programs assuming a resolvable URL might still break, but only if they were poorly crafted indeed would they hang pending a time out.  The whole issue could largely be mooted by clarifying the purpose and intended usage of _alias.dictionary_uri in its definition.  That need not prevent programs from attempting to resolve dictionary URIs, but if it specified that dictionary URIs might be permanently unresolvable then programmers would know to prepare for that possibility.
>>>   We already do something very similar to this with
>>> alternate conformers and with NMR model numbers.  It
>>> really is a simply concept for organizing information
>>> that belongs in groups, in this case the group of
>>> DDL1 or DDL2 or DDLm or ... style tags.
>> I think that makes it a bit clearer to me what you want to do, but I'm still interested in the answers to my questions above.  I'm a bit uncomfortable with defining generic groups of aliases with per-dictionary semantics, if that's indeed what you're proposing.  For one thing, it does not play well with dictionary merging.  For another, the meaning of the groupings is nowhere defined, at least not without adding at least one more data names to DDLm for that purpose.
>> On the other hand, data names have at least one natural grouping: the dictionaries in which they are defined.  This grouping is already modeled in DDLm, and as far as I can tell, it is conceptually a perfect fit for what you want to do.
>> That doesn't necessarily mean that there is no use for a more general grouping mechanism.  I am curious indeed whether there are use cases for grouping data names that do not align well with dictionaries or dictionary-defined attributes.  Can anyone suggest some?
>>>  It solves
>>> a very real problem for me with imgCIF.  It does
>>> not harm to anybody else.  If nobody uses it in
>>> another dictionary, it still would have been a useful
>>> addition to DDLm.
>> I very much want you to have a solution to your problem, and I have suggested one that still seems absolutely natural to me.  It may be that there are better alternatives, and perhaps even that tag style would be one such.  Of the latter, however, I am not yet persuaded.
>> Perhaps "harm" is too charged a word, but adding an additional attribute to DDLm certainly does cost everyone else.  Every DDLm application must support all the DDLm attributes, so every additional attribute places a development and maintenance burden on multiple developers.  That incrementally slows software release cycles and introduces additional space for bugs and incompatibilities to hide.  It's a small cost for most people, but everyone pays it.  The proposed tag style is no different in that regard from any other DDLm attribute, of course, but that doesn't mean that its cost should be ignored.
>> As for whether it would be a useful addition to DDLm, that is exactly what I am trying to decide.  Potential use cases such as I solicited above would help me make that decision.
>>>   In the end, I suspect that both core and mmCIF DDLm
>>> dictionaries will be built this way, because it
>>> make it simpler and clearer and allows multi-purpose
>>> dictionaries to be self-contained and avoid the
>>> maintenance headache David spotted.
>> If by "multi-purpose dictionaries" you mean defining multiple virtual dictionaries via a single DDLm dictionary, such as you plan, then I still see the dictionary_uri as the natural way to use aliases for that purpose.  If there is a broader concept here then please help me see it.
>> Regards,
>> John
>> --
>> John C. Bollinger, Ph.D.
>> Department of Structural Biology
>> St. Jude Children's Research Hospital
>> Email Disclaimer:  www.stjude.org/emaildisclaimer
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