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

Dear Colleagues,

   There is an importantr part of James' suggestions that,
if Brian is willing, I think it would be a good idea
to add to the _alias.tag_style proposal and that is
a central registry of styles to facilty dictionary
merging.  The ground rules would be:

   COMCIFS approval for any style, such as DDL1, DDL2,
DDLm, etc., unless prefixed by a prefix from Brian's
prefix registry, e.g. pdbx_.  The special prefix
local_ could be used for styles for use purely
locally, i.e. for private dictionaries for which]
collisions on merging are not a concern.


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


On Thu, 20 Jan 2011, Herbert J. Bernstein wrote:

> Dear Colleagues,
>  If a DDLm dictionary is to be a fully functional replacement
> for, say, a DDL1 dictionary, a dictionary against which one
> can validate the use of purely DDL1 tags, we need a way to
> not only specify the desired DDL1 tag as an alias to the
> DDLm tag used in the dictionary, but also to specify that
> we do _not_ want to accept the DDLm tag used as the save
> frame name as the valud name.  As David has noted, in
> order not to still be maintaining both a DDL1 and a
> DDLm dictionary, we want this information _in_ the DDLm
> dictionary, so simply aliasing back to some other
> DDL1 dictionary to use it as a way to say -- "use that dictionary
> URI as the style indicator" is suboptimal. Worse, it is a
> source of future errors and confusion in that it is
> defining properties of the tag that may end up disagreeing
> with the properties we wish to actually have that we
> defined in the DDLm dictionary.
> OK, so far, so good -- all we need then is John B.'s tag-by-tag
> style preference flag to say, for this dictionary we want to
> be DDL1'ish.
> Ah, but now we say, we are in the situation of maintaining
> the core (David's problem) in which we have to maintain
> a dictionary for validation against both DDL1 and DDL2
> tag names.  Now there are times when we wish the DDL1
> alias to be the preferred alias and for both the DDL2
> and DDLm tags to fail a validation check and other times when
> we wish the DDL2 alias to be the prefeered alias and
> for both the DDL1 and DDLm tags to fail a validation check.
> Now it becomes simpler to just have a common style key,
> such as "DDL1" or "DDL2" and to select just the way we
> do for alternate conformers on that key.
> OK, that was not so bad, but now we are at, say, the PDB
> and in addition to having DDL1 and DDL2 style tags from
> the core, we also have prefixed tags (pdbx) that should
> eventually get promoted to be prefix-free.  Now we can
> use the styles to validate for strict use of
> the prefixes when we are producing output that we want
> to be certain actually does use the prefixes, or
> relax the validation to allow both the prefixed and promoted
> tags, or go strict again on the far side to be sure be
> are only producting promoted tags.
> Note that none of these style based input validation choices
> are based on the choice of dictionary -- it is one dictionary,
> so it does not really help to be maintaining the styles
> dictionary by dictionary.  The grain of identification is
> too coarse, and involves multiple maintenance issues when
> in reality only one, nice new, DDLm dictionary needs to be
> maintained.
> On the output side, essentially the same issues arise, but
> there are fewer users, but as I said, it is a harmless
> addition to the DDLm spec for those who do not wish to
> be aware of it, and for those of use for whom it is
> useful, it really is useful.
> The fundamental diagreement is on whether we will have
> to have a DDL1 dictionary, a DDL2 dictionary, a DDLm
> dictionary, a prefix dictionary, etc., and plant them
> on assorted web sites, or just one DDLm dictionary that
> handles everything and can be local or remote or in
> local and remote pieces without changing the behavior
> of the validation or of the output.
> I hope that those who are uncomfortable with this change
> will reconsider and support it.  Thanks to David's clear
> thinking it is a clean, simple and useful idea, much
> better than my original import suggestion.
> Please support it.
> 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 Thu, 20 Jan 2011, James Hester wrote:
>> 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
>> ftp://ftp.iucr.org/pub/cifdics/cifdic.register).
>> 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.
>> James.
>> 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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