Both the approach used and the progress made in the assignment of structure types to the crystal structures contained in the ICSD database are reported. Extending earlier work, an hierarchical set of criteria for the separation of isopointal structures into isoconfigurational structure types is used. It is shown how these criteria, which include the space group (number), Wyckoff sequence and Pearson symbol, c/a ratio, ranges, ANX formulae and, in certain cases, the necessary elements and forbidden elements, may be used to uniquely identify the representative structure types of the compounds contained in the ICSD database.

MEETINGS C130 reaches beyond the limits of the usual 'isoelemental' concept. Introduction of small but substantial changes into distinct homologous structures leads to plesiotypes. Structures in which one set of layers/slabs is identical (or homologous) for the entire family whereas the alternating set differs from a member to a member are merotypes. Besides 'proper' (OD-and non-OD polytypes), with structurally unmodified layers, 'improper' polytypes can be recognized, with modifications of component layers, as well as pseudopolytypes between which pronounced changes in bonding patterns occur, and endopolytypes in which only, e.g., the cation component is subject to polytypy whereas the anionic framework remains (in principle) unchanged. Non-commensurability and semicommensurability can lead to polytypism.

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