|dc.description.abstract||Time-by-Example (TBE) is a user-friendly query language designed specifically for historical relational databases. It follows the graphical structure and the example query concept of QBE,
and employs the hierarchical arrangement of subqueries of Abe and
STBE. Similar to STBE, TBE handles set- and simple-valued attributes. In addition, to handle time, TBE is capable of manipulating
triplet- and set-triplet-valued attributes.
The underlying data model used in TBE is an extended relational
data model in which nonfirst normal form relations and attribute time
stamping (in contrast to tuple time stamping) are used. A triplet is a
3-tuple whose components are the lower and upper bounds of a time
interval and a value valid over the interval. A triplet is used as a timestamped value of a time-dependent attribute. Set-valued time-dependent attributes are modeled by sets of triplets.
To process TBE queries and to define a historical relational algebra
(HRA), standard operators of the relational algebra and the packlunpack operators of [Zl] are augmented by triplet-decomposition, tripletformation, slice, and drop-time operators. Methodologies for translating TBE queries into HRA expressions and for constructing their parse
trees are presented.||en_US