Browsing by Author "Tansel, A. U."

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    The expressive power of temporal relational query languages
    (IEEE, 1997) Tansel, A. U.; Tin, E.
    We consider the representation of temporal data based on tuple and attribute timestamping. We identify the requirements in modeling temporal data and elaborate on their implications in the expressive power of temporal query languages. We introduce a temporal relational data model where N1NF relations and attribute timestamping are used and one level of nesting is allowed. For this model, a nested relational tuple calculus (NTC) is defined. We follow a comparative approach in evaluating the expressive power of temporal query languages, using NTC as a metric and comparing it with the existing temporal query languages. We prove that NTC subsumes the expressive power of these query languages. We also demonstrate how various temporal relational models can be obtained from our temporal relations by NTC and give equivalent NTC expressions for their languages. Furthermore, we show the equivalence of intervals and temporal elements (sets) as timestamps in our model. © 1997 IEEE.
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    On Roth, Korth, and Silberschatz's extended algebra and calculus for nested relational databases
    (1992) Tansel, A. U.; Garnett, Lucy
    We discuss the issues encountered in the extended algebra and calculus languages for nested relations defined by Roth, Korth, and Silberschatz. Their equivalence proof between algebra and calculus fails because of the keying problems and the use of extended set operations. Extended set operations also have unintended side effects. Furthermore, their calculus seems to allow the generation of power sets, thus making it more powerful than their algebra.
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    Time-by-example query language for historical databases
    (IEEE, 1989) Tansel, A. U.; Arkun, M. E.; Ozsoyoglu, G.
    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.