Re: Please advise regarding a design of CIF dictionaries for materialproperties

Dear COMCIFS members,

I have a question about the design of domain-specific CIF dictionaries
and would like to ask for your advise (and please accept my apologies
and let me know if there is a better mailing list to ask for such
questions).

I am currently participating in the design of CIF dictionary for the
Material Properties Open Database (MPOD) that intends to store all
published experimentally measured crystal properties, such as elasticity
tensors, dielectric permeability and so forth. All in all there should
be about 50 different tensors.

Each tensor can be measured at different temperatures or pressures. To
preset data convenietly, for both humans and computers, we curretnly
plan to put each tensors' measurements into a separate loop. Since tag
names may not be repeated int the same data block, we will have to
define similar measurement condition tags for each tensor:

_prop_elastic_stiffness_temperature
_prop_piezoelectric_temperature

(_prop_ is a prefix registered for MPOD in the IUCr prefix list).

Now, although this is only a small overhead in CIFs, it would be an
overkill to specify all these tags separately in a dictionary. Thus, I
would like to "contract" the definition of all
_prop_<property>_temperature tags into one dictionary datablock:

data_prop_temperature
loop_
_name '_prop_elastic_stiffness_temperature'
      '_prop_piezoelectric_temperature'
      # Other names will follow and may be added in the future releases
      # of the dictionary
_type             numb
_type_conditions  esd
_category         prop # or prop_temperature ? or prop_elastic?
_list             both
_description
;
   Specifies measurement temperature of a property in Kelvins.
;
_example
;
   Please see below in this mail...
;

Now, my questions are -- is there a problem if:

a) tags of the same property are split into several loops in data CIFs?

_description
;
   Specifies temperature in Kelvin at which the peozoelectric tensor was measured. 
;

b) one dictionary data block describes names that are potentially in
different categories (but otherwise have the same characteristics)? For
example, would the dictionary entry above be considered correct if we
declare _prop_elastic_stiffness_temperature to be in
'prop_elastic_stiffness' category, and _prop_piezoelectric_temperature
to be in 'prop_piezoelectric' category, and still have one dictionary
datablock to specify their properties?

b') or the category is so inclusive that it describes data spanning
several loops (like '_prop_' category in the above example)?

c) data_... block name in the dictionary no longer matches tag name. I
guess this should not be a problem... Is it?

d) would it break anything if category name is not the prefix of the tag
(e.g. declaring _prop_piezoelectric_temperature to have category
_prop_temperature, to describe all temperature tags in one data block)?

e) Any other anticipated problems?

Sincerely yours,
Saulius

PS. We have toyed with two other representations, one putting all
tensors into one loop, but they seem much worse (would require lots of
'.' fields and would result in severely denormalised relational tables).

PPS: data examples with the proposed tags:

The CIF would look like

loop_
_prop_elastic_stiffness_label
_prop_elastic_stiffness_temperature
_prop_elastic_stiffness_c11
_prop_elastic_stiffness_c12
_prop_elastic_stiffness_c13
_prop_elastic_stiffness_c22
_prop_elastic_stiffness_c23
_prop_elastic_stiffness_c33
_prop_elastic_stiffness_c44
_prop_elastic_stiffness_c55
_prop_elastic_stiffness_c66
Copper  273  375.1  -48.5  -48.5  375.1   -48.5  375.1  101.4   101.4 101.4
Copper  293  375.1  -48.5  -48.5  375.1   -48.5  375.1  101.4   101.4 101.4
Copper  313  375.1  -48.5  -48.5  375.1   -48.5  375.1  101.4   101.4 101.4

loop_
_prop_piezoelectric_label
_prop_piezoelectric_temperature
_prop_piezoelectric_frequency
_prop_piezoelectric_d15
_prop_piezoelectric_d16
_prop_piezoelectric_d21
PIN-PMN-PT 100.0 ? 2190 1022 511
PIN-PMN-PT 100.0 ? 2190 1022 511
PIN-PMN-PT 100.0 ? 2190 1022 511

and so on.

S.G.