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(63) more on pdCIF categories
- To: COMCIFS@iucr.ac.uk
- Subject: (63) more on pdCIF categories
- From: bm
- Date: Fri, 9 May 1997 20:20:33 +0100
Dear Colleagues D61.1 pdCIF categories ---------------------- I attach Syd Hall's response to the question of imposing a tighter category model on the pdCIF dictionary. S> Brian: I have read through the latest communiques and in a way am relieved S> that this category business will get further airing with respect to the S> powder dictionary. S> S> As you indicated I have had reservations about the lack of correspondence S> between some of the datanames and their categories for some time (my mail S> goes back to the early days of the pd definitions). I suspect that the S> departure of categories from names evolved as the list structures of the S> powder definitions evolved (divergently)...BT can fill us in on that S> history. My reminder to COMCIFS about these departures was so that we S> understood that they represented a change in philosophy from earlier S> dictionaries and a different approach for some software (those using the S> data name rather than the explicit category definition to check category). S> S> However, I want to emphasise that am not categorically (:->) against the S> separation of category and dataname naming conventions, because this is S> strictly an "application matter", as opposed to a requirement of the STAR S> syntax (see p506, JCICS, 34, 1994 for explanation and examples). By the way S> it is also not part of the STAR DDL definitions (JCSCI 35, 819-825, 1995). S> S> On the other hand, the association between "category" and the construction S> of datanames is very strongly implied in the original 1991 CIF core paper, S> though as far as I can see there is no EXPLICIT instruction that the data S> name MUST contain the category name in a CIF. Certainly the earlier DDL1 S> CIF dictionaries never departed from this association, and the later DDL2 S> mmCIF dictionary built this into its dot naming structure. S> S> I continue to support both the DDL1 and DDL2 efforts because they are S> appropriate to their applications. A rather pragmatic view perhaps, but we S> all need to be reminded occasionally that dictionaries are not pedantic S> exercises...and existing data handling needs must be addressed with some S> urgency. So I too do not have a particular dogma on the dataname/category S> relationship. I can see advantages and disadvantages to a strict association. S> Perhaps it would make life simpler to fix this relationship but there are S> views that the hierarchical approach of DDL2 is not only one to be considered S> in data handling, and therefore it MAY be unwise to set the relationship S> in stone at this stage. Perhaps Nick Spadaccini should comment on this. S> S> This is an important matter and I am pleased that Paula's effort and concern S> has brought it to a head! Have a good weekend, Brian
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