Each code is composed of three parts:
Currently, the only prefix defined is "T", indicating Musical works. However, additional prefixes may be defined in the future to expand the available range of identifiers and/or expand the system to additional types of works.
ISWC identifiers are commonly written the form T-123.456.789-C. The grouping is for ease of reading only; the numbers do not incorporate any information about the work's region, author, publisher, etc. Rather, they are simply issued in sequence. These separators are not required, and no other separators are allowed.
To register an ISWC, the following minimal information must be supplied:
Note: an ISWC identifies works, not recordings. ISRC can be used to identify recordings. Nor does it identify individual publications (e.g. issues of a recording on physical media, sheet music, broadcast at a particular frequency/modulation/time/location...)
Its primary purpose is in collecting society administration, and to clearly identify works in legal contracts. It would also be useful in library cataloguing.
Due to the fact that a musical work can have multiple authors, it is inevitable that, on rare occasions, a duplicate ISWC might exist and might not be detected immediately. Because of the existing business practices among collecting societies, it is not possible to simply declare an ISWC as obsolete. In such cases, as soon as they are identified, the system will deal with duplicate registrations by linking such registration records in the ISWC database and its related products.
The third element of the ISWC is the check digit. This is calculated using a MOD 10 algorithm.