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Re: CIF specification: reserved prefixes

Brian: Your change is logical and imposes no real constraints on
reserved data name prefixes. I support it.


On Tuesday, October 28, 2003, at 08:06  PM, Brian McMahon wrote:

> Dear Colleagues
> While working through the content of International Tables Volume G, I 
> have
> come upon two statements that are in flat contradiction. In the CIF
> specification, regarding the use of registered prefixes to reserve a
> namespace of data items for local use, it is stated:
>      \P 12. There is no syntactic property identifying such a reserved
>             prefix, so that software validating or otherwise handling
>             such local data names must scan the entire registry and
>             match registered prefixes against the indicated components
>             of data names. Note that reserved prefixes may themselves
>             contain underscore characters, so a maximal matching search
>             must be made.
> while in chapter 3.1, "General considerations when defining a CIF data
> item", I find I have written
> Reserved prefixes
>      To guarantee that locally devised data names may be placed without
>      name conflict in interchange data files, authors may register a
>      reserved character string for their sole use. As with the special
>      prefix _[local]_ discussed in the preceding section, the author's
>      reserved prefix is simply an underscore-bounded string within the 
> data
>      name (i.e. it may not itself include an underscore character).
> I can in fact see no useful purpose in permitting an underscore 
> *within* a
> registered prefix - it simply complicates the task of the parser. At 
> this
> stage no prefixes have been registered with an embedded underscore. I
> therefore propose to amend paragraph 12 of the CIF working spec, 
> replacing
> the final sentence by
>      "Note that reserved prefixes may not themselves contain underscore
>       characters."
> Please let me have your opinions on this as quickly as possible. I 
> shall
> continue to work on the Volume on the assumption that no objections 
> will be
> raised to this amendment.
> Regards
> Brian
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