2.6. Specification of a relational dictionary definition language (DDL2)
J. D. Westbrook, H. M. Berman and S. R. Hall
Abstract
The dictionary definition language version 2 (DDL2) extends the version 1 DDL used by the IUCr for the description of data items common to all crystallographic studies (i.e. core items). The DDL2 extensions were introduced primarily to address two issues arising during the development of a CIF dictionary for the terminology of macromolecular crystallography: the need to accurately describe the hierarchical nature of macromolecular structure and associated structural features, and the desire to encode dictionary definitions in a manner that would permit more detailed software-driven validation.
This chapter presents the attribute sets described by the DDL2 language and illustrates their relational character. DDL2 attributes are classified in categories with unique key items; these categories play the roles of tables in a relational database structure. The relationships between categories are illustrated graphically and are described in detail in the chapter.
The organization of DDL2 reflects the organization of the data model whose attributes it describes (i.e. in the mmCIF and related data dictionaries). Consequently, the dictionary of DDL2 attributes is itself constructed in the DDL2 formalism. The use of a self-referential data-description scheme allows the consistency and relational integrity of the data model to be independently verified.
The chapter provides a detailed description of each data attribute described in the DDL2 scheme.
References
Allen, F. H., Barnard, J. M.,
Cook, A. P. F. & Hall, S. R. (1995). The Molecular
Information File (MIF): core specifications of a new standard format
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Hall, S. R. (1991). The STAR File: a new
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Hall, S. R., Allen, F. H. &
Brown, I. D. (1991). The Crystallographic Information File
(CIF): a new standard archive file for crystallography.
Acta Cryst. A47, 655-685.
See also
![[web]](../graphics/www.gif){kind=small}
![[cdrom]](../graphics/cd.gif){kind=small}
HTML version
(http://www.iucr.org/iucr-top/cif/standard/cifstd1.html).
Hall, S. R. & Cook, A. P. F.
(1995). STAR Dictionary Definition Language: initial
specification. J. Chem. Inf. Comput. Sci. 35,
819-825.
Hall, S. R. & Spadaccini, N. (1994).
The STAR File: detailed specifications. J. Chem. Inf. Comput.
Sci. 34, 505-508.
Westbrook, J. D. & Hall, S. R. (1995). A dictionary definition language for macromolecular structure. http://ndbserver.rutgers.edu/mmcif/ddl.