Crystallographic Information Framework

[CIF2 logo] 


CIF2 is a new, alternative file format for use with the Crystallographic Information Framework, supplementing the original CIF format ('CIF1') developed in the early 1990s. CIF2 introduces a Unicode character set and extensions for complex data types.  Following final adjustments, CIF2 was formally approved by COMCIFS in August 2014. The CIF2 standard is described in a recent publication:  Bernstein, H. J., Bollinger, J. C., Brown, I. D., Gražulis, S., Hester, J. R., McMahon, B., Spadaccini, N., Westbrook, J. D. & Westrip, S. P. (2016). "Specification of the Crystallographic Information File format, version 2.0", J. Appl. Cryst. 49details

An annotated ISO 14977 EBNF specification is also available.

Frequently Asked Questions

How does CIF2 improve on CIF1?

CIF2 allows Unicode characters, and both matrices and tables as datavalues. It provides the more familiar triple quote (''') alternative to semicolons as multi-line string delimiters, and it disallows embedded quotes in delimited strings, simplifying parsing.

I don't need that new stuff. Can't I just stick with CIF1?

Absolutely. CIF1 was developed and promoted as an archival format, and the IUCr are committed to supporting CIF1 in perpetuity, as are the leading crystallographic database services such as the Protein Data Bank (wwPDB), CCDC, COD and ICSD. What approach your software ultimately takes will depend upon what your ecosystem of CIF providers and CIF consumers do.

What tools are available for CIF2?

The upcoming C-language CIFAPI implementation developed by John Bollinger is fully conversant with CIF1 and CIF2. Once bindings to popular programming languages are made available it would be a good choice for many projects. Links to this and other CIF2-conversant software are listed on this page.

Can I read a CIF2 format file with my CIF1 parser?

Reading a CIF2 file with a CIF1 parser will not always succeed, due to the addition of unicode characters and new types of datavalues (tables, lists, additional string delimiters) in CIF2.

However, if none of the new features are present in the CIF2 file, a CIF1 parser will succeed. A CIF datafile containing only datanames defined in current dictionaries and not using ''' or """ as delimiters will read in correctly as long as there are no undelimited datavalues starting with [ or {.

Can I write a parser that will read both CIF1 and CIF2 files?

Yes, because CIF2 files are required to begin with the characters #\#CIF_2.0. You can choose which set of parsing rules to use depending on this string.

Can I read a CIF1 format file with my strict CIF2 parser?

No, due to the header string mentioned above, and see the answer to the next question.

Can I read a CIF1 format file with my liberal CIF2 parser?

If you ignore the header string mentioned above, your chances are good of being able to read in a CIF1 file correctly. The key differences to watch out for are strings with embedded delimiters, like 'CA'T', which are forbidden in CIF2, and non-delimited strings that start with { characters, which are used to start CIF2 'Table' datavalues. Neither of these types of datavalues are particularly common.

How do I make my software CIF2-ready?

See the next questions for information specific to the particular task.

My software outputs CIF1 files. What changes should I make when outputting CIF2 files?

Firstly you should begin your files with the string #\#CIF_2.0. Then you should adjust your string datavalue output to use delimiters in most cases. At a future date, when matrix or table-valued datanames are defined by dictionaries, you should be ready to output them with correct syntax.

My software reads CIF files. How do I become CIF2 ready?

You will need to enhance your old CIF1 parser with the ability to read (possibly nested) matrix and table datastructures, to recognise triple-quoted strings, and to accept Unicode.