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Acta Cryst. (1991). A47, 655-685

Creating a CIF

A large proportion of the data included in a CIF will be generated by crystallographic software packages. The CIF example shown in Appendix II was created for publication in Acta Crystallographica Section C by the program CIFIO (Hall, 1990). However, it also contains data added manually by the authors (Willis, Beckwith & Tozer, 1991). The majority of data items in this example were requested specifically (from CIFIO) for a test Acta Crystallographica submission. Note that the missing items in this example are flagged with a `?'. Programs such as CIFIO can only output the data items present in their internal files and the `?' flag represents a simple mechanism for identifying missing items.

The use of a `?' as a missing data flag is important for two reasons: it signals the inaccessibility of a data item to the generating software, and it satisfies the STAR File requirement that each data name must be matched with a data value. The use of a `?' enables data items from other sources to be added later either manually or by software. For example, most _publ_ items will be entered manually. Manuscripts can be entered by the authors either as ASCII text or as word-processed modules (see _publ_manuscript_ fields in Appendix I). Journal staff will also, in consultation with authors, make changes in response to the detection of incorrect numerical data or to the comments of referees or Co-editors.

The provision for transmitting graphical publication data within a CIF is being investigated. The inclusion of ASCII graphical modules suitable for producing direct laser or plot diagrams (e.g. using HPGL or PostScript) has already been tested. It will also be possible for some diagrams to be generated directly from the _atom_ and _chemical_conn_ data by the journal staff. In the future it is expected that a CIF may contain encapsulated PostScript or TeX modules of text that can be transferred directly to the journals' word processing facility.

Apart from the generation of CIF's by crystallographic packages, specific standalone software has been developed to update, check and access CIF's. The Cambridge Crystallographic Data Centre is developing a program CIFER (Allen & Edgington, 1992) to facilitate the update and creation of a CIF via a menu-driven interface. This will enable a CIF to be upgraded interactively with 2D diagrams and other missing data. The program EDCIF-J (Osaki, 1991) is also designed for the interactive creation of a publication CIF. Another program, CYCLOPS (Hall, 1991b), uses the Dictionary file cifdic.C91 to validate data names in any text file, including program source code. This is an essential requirement for software developers wishing to adhere to the standard data names. Finally, the program QUASAR (Hall & Sievers, 1990) is designed to extract requested data items from a CIF in the form of another STAR File (further details of this program are given below).

It should be emphasized that CIF's are not intended solely for publication purposes. They are well suited to local archiving and data exchange. Which data are stored in a CIF, and in what order, is very much up to the user. Any CIF, whether for local or global applications, may contain a mixture of standard (IUCr defined) and non-standard (locally defined) data. This will not affect access to either category of data.

It is possible to check or to extract data from a CIF using a text editor. However, a more systematic approach is to use specific software for these purposes, such as provided by the programs CYCLOPS and QUASAR. In the next section the program QUASAR is used to illustrate a typical approach to accessing data in a CIF.

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