WHAT IS A CIF, AND HOW IS IT USED? By B. McMahon, International Union of Crystallography, 5 Abbey Square, Chester CH1 2HU, England.

The Crystallographic Information File, or CIF, is the data exchange format defined and adopted by the IUCr for the transfer of crystallographic information between laboratories, databases, journals and applications programs. It has proven successful in all these areas: for example, Acta Crystallographica Section C is typeset entirely from electronic submissions in CIF format, and the data in the resultant papers are transferred by ftp direct to the Cambridge Crystallographic Data Centre. The highly structured file format allows a large amount of automated checking and validation of the included data, and the Union's goal of achieving a free flow of uncorrupted data from refinement program through to publication and archive has been largely achieved.

As the CIF project has developed, it has become clear that there are more profound benefits to be reaped. Precise definitions have been drawn up of the scientific terms that should be universally recognised within the discipline. The dictionary that holds these definitions is an electronic file. This file can also store machine-readable information about the ranges of permitted values for the quantities described, and about their interdependence. This gives rise to the possibility of writing sophisticated software able to manipulate novel concepts in the science as they are developed.

A technical committee of the IUCr (known as COMCIFS) maintains and develops dictionaries of terms that may be used in universal CIF applications.

As equipment manufacturers continue to add CIF capability to their software, as increasingly powerful applications are developed, as the IUCr makes available its archive of structures in CIF format, so will this novel data format continue to evolve into the universal language of crystallography.