I began my work with a database of tags and subfields that had been developed by Tom Delsey in his “Functional Analysis of MARC21 Bibliographic and Authority Formats” [2]. I was able to supplement this using the tables of fixed fields and their values from marc.pm modules [3]. If nothing else, this task made me painfully aware that we do not have a sharable machine-readable form of our own data format. The MARC21 standard is represented only by an online text, something that is rather astonishing if you think about it. Anyone wishing to develop applications for MARC21 must create their own usable version. My own database still lacks definitions and descriptions, and those will probably need to be added by screen-scraping hundreds of screens from the LC web site.