The International Standard Musical Work Code (ISWC) is a unique identifier for musical works, similar to ISBN for books.
Each code is composed of three parts:[1] Currently, the only prefix defined is "T", indicating Musical works.
The grouping is for ease of reading only; the numbers do not incorporate any information about the work's region, author, publisher, etc.
The first ISWC was assigned in 1995, for the song "Dancing Queen" by ABBA; the code is T-000.000.001-0.
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.
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.