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. 3.1, p. 80

Section 3.1.6.3. Category groupings

B. McMahona*

aInternational Union of Crystallography, 5 Abbey Square, Chester CH1 2HU, England
Correspondence e-mail: bm@iucr.org

3.1.6.3. Category groupings

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In the DDL2 data model, a category of data corresponds to a set of related data items that may be stored in a single relational database table. A number of such tables may collectively describe the complete properties of some physical object. This is expressed formally by assigning the same label ( _category_group.id) to the relevant categories. While relationships between categories are implied in DDL1 dictionaries by the hierarchical structure of the names of data items, in DDL2 dictionaries the relationships are formally stated.

For subcategories, the category-group relationships present in the dictionary are listed in a separate looped list. Example 3.1.6.3[link] is an extract from the macromolecular dictionary. The inclusive_group entry shows the common parentage of all categories (and ultimately all data items) in the dictionary.

Example 3.1.6.3. Category groups in a DDL2 dictionary.

[Scheme scheme12]








































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