# unnest

## unnest

(ʌnˈnɛst)
vb (tr)
to disturb or remove from a nest
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
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The semantics is described by means of an extended relational algebra with new operators: Group by, Unnest, Extend, Substitute, Rename, Powerset, which transform a relational table into an object-relational table (i.e.
Monoid comprehension calculus treats operations over multiple collection types, aggregates, and quantifiers in a similar way, resulting in a uniform method to unnest queries, regardless of their type of nesting.
Comprehensions of the form [direct sum]{ e [] [bar]r, v [left arrow] ??{f [] [bar]s}(u), [bar]q} are very difficult to normalize and unnest.
* unnest, [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], returns the collection of all pairs (x, y) for each x [element of] X and for each y [element of] x.path that satisfy the predicate p(x, y).
Note that Rule (C2) compiles every comprehension generator into an unnest. This step may not be necessary if [e.sub.2] is a class extent, in which case it may be better compiled into a join.
The unnest operator, [[micro].sub.e.children], accepts the stream of tuples of type set(< e: Employee >) and constructs a stream of tuples of type set(< e: Employee, c: Person >), connecting each employee with one of his or her children.
The semantics of these operators cannot be given in terms of the monoid calculus if the outer query constructs a nonidempotent collection, since information about the exact number of copies of the data in the outer query may be lost after the outer join or unnest.
The rules in Figure 10 unnest all nested comprehensions.
Even though Rule (C11) has a precondition, it will eventually be applied to unnest any nested query in a predicate.
The most famous operations on complex-objects are nest and unnest. Nest/unnest in IQL resembles the expression of these operations in the language COL [Abiteboul and Grumbach 1988; Abiteboul et al.
We want to unnest [R.sub.1] into [R.sub.2], and then nest [R.sub.2] into[R.sub.3].
La semantica se describe por medio de una extension del algebra relacional con nuevos operadores: Group by (G), Unnest (h), Extended (E), Substitute (a), Rename (r), Powerset (R), que permiten transformar una relacion con el fin de descubrir reglas de asociacion [26] [27].

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