A library and program for the creation, management, and installation of schema updates (called migrations) for a relational database. In particular, this package lets the migration author express explicit dependencies between migrations and the management tool automatically installs or reverts migrations accordingly, using transactions for safety. This package is written to support a number of different databases. For packages that support specific databases using this library, see packages named "dbmigrations-BACKEND". Each package provides an executable "moo-BACKEND" for managing migrations. Usage information for the "moo-" executables can be found in MOO.TXT in this package. This package also includes a conformance test suite to ensure that backend implementations respect the library's required semantics.