entropy of data....?

[Graham Toal]

: Hasn't someone come up with a name for this like "Entropy of the data is 30 
: days" or... "the half-life of the data is 15 days".  This is a critical 
: value when looking at it from a military point of view.  If you can't decode 
: enemy plan for attack before a certain date/time then the info is 
: useless....

That betrays a bit of ignorance about the meaning of 'half-life'.

I think the word you're looking for is 'lifetime'.

G