The is of the Digital Object and the is of the Artifact | The Signal: Digital Preservation
As we’ve explained before, digital objects have a somewhat curious nature. Encoded in bits, you need to check to make sure that a given digital object is actually the same thing you started with. Thankfully, we have the ability to compute checksums, or cryptographic hashes. This involves using algorithms to generate strings of characters that serve as identifiers for digital objects. Under normal non-tampered with conditions, these hash values more uniquely identify files than DNA uniquely identifies individuals.  When we generate these hashes for digital objects to audit digital content we want to know if an object is the same as it was before.  Is it still bit-for-bit the exact same thing?  It is important to note that the “is” in that last sentence is only one tradition of saying that something is still the same.

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Source: http://blogs.loc.gov/digitalpreservation/2012/10/the-is-of-the-digital-object-and-the-is-of-the-artifact/
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