What is negative property in the context of database design? -

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i read in scientific literature lossy join negative property in relational database design. negative property in context of database design? there called positive property well?

lossy join means lossy decomposition , join operation. example, given following relation, r:

r +-----+-----+ |   | b   |  |-----|-----| | foo | 100 |  | foo | 200 |  | bar | 100 |  +-----+-----+

the following decomposition new relations r1 , r2 "lossy" because isn't possible reconstruct original tuples of r joining r1 , r2.

r1         r2 +-----+    +-----+ |   |    | b   | |-----|    |-----| | foo |    | 100 | | bar |    | 200 | +-----+    +-----+

"lossy" means information lost after decomposition , join.

in database design theory non-lossy decompositions of interest when considering whether possible alternative database designs can faithfully represent same information. out of context it's not meaningful lossiness either positive or negative thing - it's property decomposition-join may or may not have.


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