XmlmmCIF equivalent: struct_ref Data items in the STRUCT_REF category allow the author of a data block to relate the entities or biological units described in that data block to information archived in external databases. For references to the sequence of a polymer, the value of the data item _struct_ref.seq_align is used to indicate whether the correspondence between the sequence of the entity or biological unit in the data block and the sequence in the referenced database entry is 'complete' or 'partial'. If this value is 'partial', the region (or regions) of the alignment may be delimited using data items in the STRUCT_REF_SEQ category. Also for references to the sequence of a polymer, the value of _struct_ref.seq_dif is used to indicate whether or not the two sequences contain point differences. If the value is yes, the differences may be identified and annotated using data items in the STRUCT_REF_SEQ_DIF category. XmlmmCIF equivalent: struct_ref/biol_id This data item is a pointer to _struct_biol.id in the STRUCT_BIOL category. XmlmmCIF equivalent: struct_ref/db_code The code for this entity or biological unit or for a closely related entity or biological unit in the named database. XmlmmCIF equivalent: struct_ref/db_name The name of the database containing reference information about this entity or biological unit. XmlmmCIF equivalent: struct_ref/details A description of special aspects of the relationship between the entity or biological unit described in the data block and the referenced database entry. XmlmmCIF equivalent: struct_ref/entity_id This data item is a pointer to _entity.id in the ENTITY category. XmlmmCIF equivalent: struct_ref/pdbx_align_begin Beginning index in the chemical sequence from the reference database. XmlmmCIF equivalent: struct_ref/pdbx_db_accession Accession code of the reference database. XmlmmCIF equivalent: struct_ref/pdbx_seq_one_letter_code Database chemical sequence expressed as string of one-letter amino acid codes. XmlmmCIF equivalent: struct_ref/seq_align A flag to indicate the scope of the alignment between the sequence of the entity or biological unit described in the data block and the referenced database entry. 'entire' indicates that alignment spans the entire length of both sequences (although point differences may occur, and can be annotated using the data items in the STRUCT_REF_SEQ_DIF category). 'partial' indicates a partial alignment, and the region (or regions) of the alignment may be delimited using data items in the STRUCT_REF_SEQ category. This data item may also take the value '.', indicating that the reference is not to a sequence. XmlmmCIF equivalent: struct_ref/seq_dif A flag to indicate the presence ('yes') or absence ('no') of point differences between the sequence of the entity or biological unit described in the data block and the referenced database entry. This data item may also take the value '.', indicating that the reference is not to a sequence. XmlmmCIF equivalent: struct_ref/id The value of _struct_ref.id must uniquely identify a record in the STRUCT_REF list. Note that this item need not be a number; it can be any unique identifier.