**UDO** User defined operator.

**UDT** User defined type.

**unary** Of degree one.

**UNGROUP** *See* ungrouping.

**ungrouping** Let *s* be a relation with an attribute *YR* of type RELATION {*Y*}, and let {*X*} be the set of all attributes of *s* except *YR*. Let {*Y*} have attributes *Y1, Y2, . . ., Yn*; also, let {*X*} not contain any attribute with the same name as any of *Y1, Y2, . . ., Yn*. Then the ungrouping *s* UNGROUP (*YR*) is another relation *r*. The heading of *r* consists of the set theory union of {*X*} and {*Y*}. As for the body, let *z* be a relation with heading consisting of {*X*} extended with an attribute *YT*, of type TUPLE {*Y*}, and body defined as follows: for each tuple of *s*, *z* contains a set of tuples, one (*t*, say) for each tuple in the *YR* value in that *s* tuple; each ...

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