numbering scheme

There are many different numbering schemes for assigning nominal numbers to entities. These generally require an agreed set of rules, or a central coordinator. The schemes can be considered to be examples of a primary key of a database management system table, whose table definitions require a database design. Numbering schemes include:ChemistryCAS registry numbers for chemical compoundsEC numbers for identifying enzymesUN numbers for (classes of) hazardous substances E numbers for food additives
See more at Wikipedia.org...