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RE: Standard uncertainties (SU) in the DDLm dictionary

  • Subject: RE: Standard uncertainties (SU) in the DDLm dictionary
  • From: "Bollinger, John C" <John.Bollinger@xxxxxxxxxx>
  • Date: Wed, 12 Apr 2017 13:12:53 +0000
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Hello Antanas,

At 4:45 AM, Wednesday, April 12, 2017, Antanas Vaitkus wrote:

> 1) Can the ways of expressing SU be used interchangeably?
> [...]
> 2) Does one way of expressing SU values have precedence over the other?

It sounds like you may be trying to apply the DDLm definition to the wrong scope.  DDLm, like the DDLs that came before it, defines data names with which to write *dictionaries*.  It is such dictionaries that express the language and constraints for CIF data files.  Thus, when DDLm says that an item with purpose “Measurand” has an SU that may be expressed in multiple ways, it is extending that option to the dictionary in which such an item is defined.  How the standard uncertainties are to be represented in data files is to be defined by the dictionary; it is not an option extended to data files (unless the dictionary makes it so).

This particular freedom accommodates the variety of current practices.  DDL2 dictionaries, especially mmCIF, define separate data names for standard uncertainties, and documents must use that mechanism to convey them in order to be valid with respect to those dictionaries.  DDL1 dictionaries such as Core CIF, on the other hand, generally do not define separate data names for standard uncertainties, and documents must therefore use the parenthesized form in order to be valid with respect to *those* dictionaries.  The DDLm versions of the Core and mmCIF dictionaries do not afford any different options to data files than the original DDL1 and DDL2 dictionaries do.



John C. Bollinger, Ph.D.
Computing and X-Ray Scientist
Department of Structural Biology
St. Jude Children's Research Hospital


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