Specification of the Crystallographic Information File (CIF)

The Crystallographic Information File (CIF) is an electronic file containing specific data items relevant to crystallographic structure determinations and descriptions in the form of numbers and text, which are represented as ASCII character strings. The structure and format of a CIF are based on a restricted subset of the syntax of a Self-defining Text Archive and Retrieval (STAR) File. The CIF is intended as a general, flexible and extensible free-format file suitable for the transmission, storage and publication of crystallographic data. Since 1990 it has been recommended by the International Union of Crystallography as the preferred data structure for the exchange of data. This chapter provides a detailed description of the syntax features of a CIF and its conventions for associating meaning or semantic content to included data. Particular care is taken to describe how the file format handles issues of portability and archival integrity. The chapter includes the complete official specification, and a formal grammar in extended Backus–Naur form. This chapter is also available as HTML from the International Tables Online site hosted by the IUCr.