Because it has such a large database, the OCLC record number has become a de facto identifier for books and other resources. The OCLC number is in every one of those (now restricted) records in thousands of library systems across the globe. But if we want to get free of OCLC, we obviously can't use their identifier.
The difficulty is getting an identifier into the millions and millions (or 1 sagan) of records in library databases. The options seem to be
1) develop a good, solid, computable identifier from the bibliographic data itself (nearly impossible)
2) create a switching system that will take bibliographic information as input and switch to a common identifier (like ASIN) (maybe more plausible?)
You can measure a programmer's perspective by noting his attitude on the continuing viability of FORTRAN. -- Alan Perlis