Signatures
A signature "summarises" the data from one tuple
A tuple consists of n attribute values A1 .. An
A codeword cw(Ai) is
- a bit-string, m bits long, where k bits are set to 1 (k ≪ m)
- derived from the value of a single attribute Ai
A tuple descriptor (signature) is built by combining cw(Ai), i=1..n
- combine by overlaying codewords (bitwise-OR)
- aim to have roughly half of the bits set to 1
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