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. 3.6, pp. 194-195

Section 3.6.9.2. Links between data blocks

P. M. D. Fitzgerald,a* J. D. Westbrook,b P. E. Bourne,c B. McMahon,d K. D. Watenpaughe and H. M. Bermanf

aMerck Research Laboratories, Rahway, New Jersey, USA,bProtein Data Bank, Research Collaboratory for Structural Bioinformatics, Rutgers, The State University of New Jersey, Department of Chemistry and Chemical Biology, 610 Taylor Road, Piscataway, New Jersey, USA,cResearch Collaboratory for Structural Bioinformatics, San Diego Supercomputer Center, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0537, USA,dInternational Union of Crystallography, 5 Abbey Square, Chester CH1 2HU, England,eretired; formerly Structural, Analytical and Medicinal Chemistry, Pharmacia Corporation, Kalamazoo, Michigan, USA, and fProtein Data Bank, Research Collaboratory for Structural Bioinformatics, Rutgers, The State University of New Jersey, Department of Chemistry and Chemical Biology, 610 Taylor Road, Piscataway, New Jersey, USA
Correspondence e-mail:  paula_fitzgerald@merck.com

3.6.9.2. Links between data blocks

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The categories describing links between data blocks are as follows:

ENTRY group
 ENTRY
 ENTRY_LINK
AUDIT group
 AUDIT_LINK

Data items in these categories are as follows:

(a) ENTRY [Scheme scheme213]

(b) ENTRY_LINK [Scheme scheme214]

(c) AUDIT_LINK [Scheme scheme215]

The bullet ([\bullet]) indicates a category key. Where multiple items within a category are marked with a bullet, they must be taken together to form a compound key. The arrow ([\rightarrow]) is a reference to a parent data item. Items in italics have aliases in the core CIF dictionary formed by changing the full stop (.) to an underscore (_).

The sole data item in the category ENTRY, _entry.id, is a label that identifies the current data block. This label is used as the formal key in several categories that record information that is relevant to the entire data block (e.g. _cell.entry_id, _geom.entry_id), so care should be taken to select a label that is informative and unique.

Data items in the ENTRY_LINK category record the relationships between the current data block and other data blocks within the current file which may be referenced in the current data block. Since there are no formal constraints on the value of _entry.id assigned to each data block, authors must take care to ensure that an mmCIF comprised of several distinct data blocks uses a different value for _entry.id in each block.

As mentioned in the introductory paragraph of Section 3.6.9[link] , the ENTRY_LINK category is used in mmCIF applications instead of the core category AUDIT_LINK. The latter is retained formally in the mmCIF dictionary for strict compatibility with the core dictionary, and the data items in this category, _audit_link.blockcode and _audit_link.block_description, are aliased to corresponding core data names (see Section 3.2.6.1[link] ). Their use is not recommended in mmCIF applications.








































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