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

Dear Saulius,

I would echo Herbert's advice.  It is important to keep everything in the right place even if it does increase the size of the dictionary.  In particular it is important to make sure that the transformation to DDLm will create no problems.  DDL1 took some shortcuts before we realized the importance of avoiding them.

I have more comments below.

Saulius Grazulis wrote:
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

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_ 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:

_name '_prop_elastic_stiffness_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
   Specifies measurement temperature of a property in Kelvins.
   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?
Although temperature is a single property, the temperatures at which different properties are measured are in principle different temperatures.  They will appear in different loops, but they are not the same property.  The description should be more specific in the example above, e.g.,
   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?
This should be avoided.  It has been used in DDL1, but is not allowed in DDLm.  Yes, it makes the dictionary larger, but it keeps everything in the right place.  In DDLm the duplication is minimized by the ability to insert the same common description of temperature into many different definitions in the dictionary.

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?
It is not a problem in DDLm, I am not sure about DDL1, but it could be confusing.  Best avoided.

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)?
In DDL1 this sometimes happens.  In DDLm the name is constructed out of he category and the item name which might make transformation to DDLm problematic.  Best avoided.

End of my comments

David Brown

e) Any other anticipated problems?

Sincerely yours,

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

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

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.

fn:I.David Brown
org:McMaster University;Brockhouse Institute for Materials Research
adr:;;King St. W;Hamilton;Ontario;L8S 4M1;Canada
title:Professor Emeritus
tel;work:+905 525 9140 x 24710
tel;fax:+905 521 2773

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