3 . 6 . Classification and Use of Macromolecular Data

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, 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). Their use is not recommended in mmCIF applications.