Abstract
A variety of approaches for improved scientific data representation is being explored. The approach described in this chapter, which has been developed under the auspices of the International Union of Crystallography (IUCr), is to extend the Crystallographic Information File (CIF) data representation used for describing small-molecule structures and associated diffraction experiments. This extension is referred to as the “macromolecular Crystallographic Information File (mmCIF)” and is discussed in the chapter. The chapter covers the history of mmCIF, similarities to and differences from the Protein Data Bank (PDB) format, contents of the mmCIF dictionary, and the way to represent structures using mmCIF. The mmCIF home page contains a historic description of the development of the dictionary, current versions of the dictionary in text and HyperText markup language (HTML) formats, software tools, archives of the mmCIF discussion list, and a detailed online tutorial. It is anticipated that full use of the expressive power of mmCIF will be made only when existing structure solution, refinement programs are modified to maintain mmCIF data items and software tools are developed to help prepare and use an mmCIF effectively.