ENSURING THE LONGEVITY OF DIGITAL DOCUMENTS

If digital documents and their programs are to be saved, their migration must must not modify their bit streams, beacuse programs and their files can be corrupted by the slightest change. If such changes are unavoidable, they must be reversible without loss. More over, one must record enough detail about each transformation to allow reconstruction of the original encoding of the bit stream. Although bit streams can be designed to be immune to any expected change, future migration may introduce unextpected alterations. Similarly, encryption makes it impossible to recover an original bit stream without the decryption key.