Section 3.1.10.2. Overview of category classification

Table 3.1.10.1 provides an informal classification at a high level of the category groups represented in each of the CIF dictionaries in this volume. Related category groups are clustered within the table in families sharing a common function. The five families (a) to (e) in Table 3.1.10.1 refer to: the crystallographic experiment itself; the processing and analysis of data from the experiment; the derived structural model; the reporting and publication of the results; and general auditing of the file itself, its purpose, authorship, history and links to other data sets, i.e. the file metadata. Detailed discussions of the individual categories (and formal category groups for DDL2 dictionaries) will be found in the relevant chapters in the rest of this part of the volume.

Table 3.1.10.1 shows the different characters of the seven dictionaries. The macromolecular dictionary (mmcif_std.dic; Chapter 4.5 ) contains an embedded version of the core dictionary (cif_core.dic; Chapter 4.1 ) in DDL2 format and so includes all the categories defined in the core. However, it extends the description of the structural model extensively by introducing families of categories for the description of chemical components of a macromolecular structure (ENTITY) and for the detailed description of the structure itself (STRUCT). New categories are also introduced to describe the phasing of the structure and the SOFTWARE category allows the inclusion of more details of computational techniques than the core COMPUTING category does.

The other dictionaries are purely extensions which either introduce new data names (and occasionally new categories) into existing category groups or, where necessary, introduce completely new groups of categories.

The powder dictionary (cif_pd.dic; Chapter 4.2 ) contains several new category groups reflecting the need for substantially different methods of describing the experiment and analysing the data, as well as a need for the structural model to be able to handle multiple crystalline phases. The modulated structures dictionary (cif_ms.dic; Chapter 4.3 ) introduces no new category groups, but does introduce several new data names and categories within the existing framework. The electron density dictionary (cif_rho.dic; Chapter 4.4 ) introduces two new categories within an existing category group. The image CIF dictionary (cif_img.dic; Chapter 4.6 ) has several new categories that characterize arrays of data from two-dimensional X-ray detectors and the consequent detailed descriptions of the relevant axes within the experimental setup. The symmetry dictionary (cif_sym.dic; Chapter 4.7 ) was commissioned specifically to replace the symmetry categories in the core dictionary with a more detailed treatment.