Abstract
A minimal extension of relational data model for logical modeling of the category of time in databases is offered. The time is considered as a totally ordered set. In the frame of suggested datamodel the homogeneous model of representation of time in relations is adopted. Allowing the homogeneity, the modeling of the temporal aspect of databases is achieved by means of two temporal attributes. The temporal attribute is considered as abstract data type. A formal definition of temporal relation which is based on abstraction of generalization is given. The semantics of operators update and delete is changed. A temporal algebra and calculus are developed. Also new aggregate functions are suggested considering the time aspect of the object behavior in the given enterprise. In order to give temporal integrity constrains closed formulas are used. The problems of partial support of evolution of the database schemes are considered.
Highlights
A great deal of research both in the area of DM and, in particular, in relational models has been done after the publications of early works of E
The following semantics is suggested for the operation r s: L;validr0 n L;validL;validr0 Qs n r0; where Q is the set of attributes of the temporal relation S without temporal attributes
The modeling of the temporal aspect of DB is achieved by means of two temporal attributes
Summary
A great deal of research both in the area of DM and, in particular, in relational models has been done after the publications of early works of E. According to the homogeneous model, temporal periods, during which the values of properties of the object maintain true, are the same for all values of attributes of a tuple of relations. Such a model is offered in [7] and is assumed in many papers based on relational DM. The values of properties of the object, which appear in some DMT, are assumed to have the property of persistence This means that their interval of existence goes maximally far to the right by time axis. In the future the BNF will be used as a metalanguage for syntax constructions
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