Welcome to the Metadata Millennium: A Complete Overview of What Metadata Can Do for Publishers
Another key standard (also maintained by BISG in the U.S.) is BISAC (Book Industry Standards and Communications) Subject Headings, also known as BISAC Codes. This is a rich subject taxonomy that was originally developed for the organization of the bookshelves in bookstores, and it's almost universally used in the U.S. for providing subject information about books through the supply chain and ultimately to the end users (aka "customers") who need to find and buy the books. There are similar standards in most other countries.
Do you see a problem lurking here? Now that books are a global phenomenon, we need a common subject classification scheme that can work in all countries and across all languages. And we've got one: as of last year, Thema provides just that. It was developed through the cooperation of publishing industry organizations throughout the world. It was published amazingly quickly, and it's being rapidly adopted. In some countries it will replace their current scheme; in others, like the U.S., it will be used in parallel. The BISG recommends that publishers use both Thema and BISAC, primarily because BISAC is still so firmly entrenched in U.S. bookselling, and also because it is much more expressive than Thema at a detailed level.
Embedded Metadata: Looking Inside
So far, we've been talking about metadata that lives outside a publication. Publishers' metadata feeds (ideally, ONIX files) and librarians' cataloguing records (ideally, MARC) are external files. Not only are they separate from the book, they're typically created by people or departments separate from the editorial and production departments that create the book itself. ONIX is managed most often by the marketing staff in a publishing house, and MARC records are created either by a cataloging service or in the library ecosystem after the book has left the publisher's hands. What about metadata that belongs in the publication itself, or is used in its creation (administrative metadata, discussed below), or that travels with the publication rather than being entirely separate (such as pedagogical or accessibility metadata)?