almost equal strings

[Roedy Green]

The rsync remote-update protocol allows rsync to transfer just the dif-
ferences between two sets of files across the network connection, using
an efficient checksum-search algorithm described in the technical
report that accompanies this package.

I'm afraid i can't tell you any more than that!

You need to figure out how to break the document into chunks at some
an optimal boundary. It would be lines or sentences for text.
It would be lines for code.
It would be records for fixed length records.
It would be UTF-strings for a DataOutputStream consisting only of
strings.

You need that to easily recognise a piece moved, something quite
common in word processing and programming. You can hash your chunks to
help find duplicates in the old and new.
--
Roedy Green Canadian Mind Products
http://mindprod.com
PM Steven Harper is fixated on the costs of implementing Kyoto, estimated as high as 1% of GDP.
However, he refuses to consider the costs of not implementing Kyoto which the
famous economist Nicholas Stern estimated at 5 to 20% of GDP