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International
Tables for Crystallography Volume G Definition and exchange of crystallographic data Edited by S. R. Hall and B. McMahon © International Union of Crystallography 2006 |
International Tables for Crystallography (2006). Vol. G. ch. 2.5, p. 56
Section 2.5.5.3. Definition example 3: irreducible data items
a
School of Biomedical and Chemical Sciences, University of Western Australia, Crawley, Perth, WA 6009, Australia, and bBCI Ltd, 46 Uppergate Road, Stannington, Sheffield S6 6BX, England |
Some data items are closely related to other data items. Fig. 2.5.5.3![[link]](/graphics/greenarr.gif)
shows the definition of the length components _cell_length_a, *_b and *_c of the crystal unit-cell metric tensor. Because of their different enumeration and units attributes, the definition blocks for cell lengths and angles are specified separately. This definition shows how data items closely related in function may be defined in the same data block. The loop_ command is used to list the multiple _name values. The attribute _type_conditions is used to indicate that these values are measurements and can have a standard uncertainty (`s.u.') value appended in parentheses e.g. 7.254(2). (The label `esd' reflects the historical but inaccurate terminology `estimated standard deviation'.) The _units and _units_detail attributes stipulate that the measurement unit of length is ångströms.
![[Figure 2.5.5.3]](/figures/Gafig2o5o5o3thm.gif)
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DDL1 definition of irreducible data items. |
