Machine tags (MachineTag) are just standard tag with extra information to extend the information in the tag. They are called machine tags because there are often use by program to get extra information from a specific work determined by its URI/location.
Blog entry about linkfingerprint : 2008-05-02 Linkfingerprint MachineTag
The initial idea came from the Internet-Draft named Link Fingerprints:
Link Fingerprints provides a backward-compatible technique for resource providers to ensure that the resource originally referenced is the same as the resource retrieved by an end user. Changes are localized to the user agent retrieving the resource, and this can automatically prevent the end user from accidentally using unintended modified data while being transparent to the end user if the data is correct.
In the Internet-Draft, the fingerprint information is located in the URI using a specific anchor mechanism. The main issue is to keep the URI readable and meaningful while keeping the integrity of the linked object. I had the idea to move the information in a system tag to avoid the issue of URI containing the fingerprint information. The additional idea is to benefit from the mass of users tagging a specific URI to validate his integrity. But also introducing the trust on the software based of the social network available in the bookmarking services like del.icio.us.
The link fingerprint machine tag also supports an additional stronger integrity format not described in the initial draft using a simple OpenPGP? detached signature.
A single URI can be tagged one time or more using the below predicate value. For example, you can tag an URI at the same time using one-way hashing in MD5 and OpenPGP? detached signature.
predicate and value are case insensitive.
md5 sha1 sha-224 sha-256 sha-384 sha-512
--lookup (default) URI --add URI
- (1)a standard Base64 encoding of the binary detached signature.
The major problem raised by OpenPGP? detached is the size of the signature. Various tagging solution has a limit for the size of a tag.