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Re: comments on coreCIF.dic 2.1

  • To: Multiple recipients of list <coredmg@iucr.org>
  • Subject: Re: comments on coreCIF.dic 2.1
  • From: Brian McMahon <bm@iucr.org>
  • Date: Sun, 17 Jan 1999 21:38:20 GMT
Dear Howard

Thank you for your most helpful review of cif_core.dic.2.1beta5. I've been
working on this over the weekend to implement suggested changes from you,
David and others. There are a few queries which I shall take up in the next
few days in direct correspondence with those who are interested, rather than
via the list.

I start with a few small inquiries for you alone: 

(2) data_chemical_[]: your suggestions for recording enantioselective
chromatography results will be welcome. As for timescale, I hope to have
this revision off my hands altogether by the end of January.

> (3) data_diffrn_measured_fraction_theta_full
>     Should not    _enumeration_range    0:1.0 really be 0.95:1.0 since 
> _diffrn_reflns_theta_full mentions 'nearly complete'. 0.0 or 0.5 do not
> seem 'nearly complete' to me!?

The usual problem about how prescriptive should _enumeration_range be. My
feeling is that the source dictionary should record only values that are
physically possible, even if not what a crystallographer would consider
reasonable or desirable. My proposals for layered dictionaries (which need
to be dusted off and formally put up for approval) allow for alternative
specifications to meet different requirements, so that your local dictionary
for validation would superimpose on this data item an _enumeration_range of
0.95:1.0. Syd's would doubtless specify 0.9999:1.0!

> (18)  data_reflns_special_details
>      In definition remove 'It should include details of the Friedel
> pairs.'. This is much better treated by data_reflns_Friedel_coverage.

With David's revision, this definition now reads 

    _name                      '_reflns_special_details'
    _category                    reflns
    _type                        char
;              Description of the properties of the reported reflection list
               that is not given in other data items.  In particular it should
               include information about the averaging (or not) of
               symmetry-equivalent reflections including Friedel pairs.

Shall we leave it now at that?

> (20) data_reflns_class_R_Fsqd_factor
>      Typos. 4 spaces around the = , squared amplitudes instead of squares ...
>     _definition
> ;           For each reflection class, the residual factor R(F^2^) calculated
>             on the squared amplitudes of the observed and calculated structure
>             factors,

Presumably I should change other instances of the phrase "squares of the
structure factors" to "squared amplitudes" ?

Best wishes

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