A key that the "outside world" uses to look up a particular
row. For example in a table of user accounts, a person's e-mail address
might be a good candidate as the logical key for the user's data. 
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</dd><dt><font color="black"><b>normalization:</b></font></dt><dd><font color="black"> Designing a data model so that no data
is replicated. We store each item of data at one place in the database
and reference it elsewhere using a foreign key.
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