International
Tables for
Crystallography
Volume G
Definition and exchange of crystallographic data
Edited by S. R. Hall and B. McMahon

International Tables for Crystallography (2006). Vol. G, ch. 2.6, p. 61

Section 2.6.2. The DDL2 presentation

J. D. Westbrook,a* H. M. Bermana and S. R. Hallb

aProtein Data Bank, Research Collaboratory for Structural Bioinformatics, Rutgers, The State University of New Jersey, Department of Chemistry and Chemical Biology, 610 Taylor Road, Piscataway, NJ 08854-8087, USA, and bSchool of Biomedical and Chemical Sciences, University of Western Australia, Crawley, Perth, WA 6009, Australia
Correspondence e-mail:  jwest@rcsb.rutgers.edu

2.6.2. The DDL2 presentation

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The syntax used in mmCIF data files and DDL2 dictionaries is a subset of the STAR syntax. Definitions in DDL2 dictionaries are encapsulated in named save frames (see Chapter 2.1[link] for a description of the STAR File syntax). A save frame is a syntactical element that begins with the save_ directive and is terminated by another save_ directive. Save frames are named by appending a text string to the save_ directive. In the mmCIF dictionary, save frames are used to encapsulate item and category definitions. The mmCIF dictionary is composed of a data block containing thousands of save frames, where each save frame contains a different definition. Save frames appear in DDL2 dictionaries but they are not used in data files. Save frames may not be nested.

DDL2 dictionary definitions typically contain a small number of items that specify the essential features of the item. Example 2.6.2.1[link] shows a save frame containing the mmCIF definition of the data item _exptl.details.

Example 2.6.2.1. Typical mmCIF definition save frame.

[Scheme scheme1]

The example definition includes: a description or text definition, the name and category of the item, a code indicating that the item is optional (not mandatory), the name of a related definition in the core CIF dictionary, and a code specifying that the data type is text. A more detailed description of the elements of the dictionary definitions is presented in the following sections.








































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