Accession and inventory codes apply to derived units and are thus issued by a particular holder of a collection (e.g. a herbarium). Loan identifiers assigned by lending or receiving institutes are not included (see Diagram 24), but seed list numbers (important in living collections) are. A single unit may receive several accession codes from different accession code systems of the same institution, and in the case of bulk accessions a single code may apply to many units. Diagram 22 details the attributes of the two entities involved.
Diagram 22: Accession or inventory code data
The attribute accession or inventory code is a textual expression of the entire code. Additional attributes could be introduced to conform to specific institutional coding schemes. A person team responsible for the assignment of the code can be named, and the assignment date may be recorded.
The accessioning or inventory system has a name (e.g.: Berlin Living Collection Accession System at B; Herbarium Willdenow Accession at B, US National Herbarium bar-code), an abbreviation, and a description. Some implementation-oriented data items may be used to maintain data integrity: the unique codes flag indicates that an error must be generated if entry of identical codes for different units is attempted; the range of permitted characters is defined by the flags digits allowed, characters allowed and upper case only together with the other allowed characters attribute (giving a list of punctuation marks or other characters permitted in the code). The suitability of the system for reference purposes is expressed by the bulk accessions flag (a single code routinely refers to several dissimilar units) and the internal use only flag (indicating that the code should not be cited). If the code is machine-readable, the specific type must be indicated (e.g. "bar-code 3 of 9").