Title: Temporal Modules: An Approach Toward Federated Temporal Databases
Authors: X.Y. Wang, S. Jajodia, V.S. Subrahmanian.
Abstract
In a federated database environment, different constituents of the federation may use different temporal models or physical representations for the temporal information. This paper introduces a new concept, called a temporal module, to resolve these mismatches among the constituents. Intuitively, a temporal module hides the implementation details of a temporal relation by exposing its information only through two windowing functions: a function associating each time point with a set of tuples and a function linking each tuple to a set of time points. A calculus-style language is given to form queries on temporal modules. Temporal modules are then extended to resolve another type of mismatch among the constituents of a federation, namely, mismatch involving different time units (e.g., month, week, and day) used in recording temporal information. Our solution to this mismatch relies on ``information conversions'' provided by each constituent. Specifically, a temporal module is extended to provide several ``windows'' to its information, each in terms of a different time unit. The first step to process a query addressed to the federation is to select suitable windows for the underlying temporal modules. In order to do so, time units are formally defined and studied. A federated temporal database model and its query language are proposed. The query language is an extension of the calculus-style language above.
This paper appears in: Proc. 1993 ACM SIGMOD Conf. on Management of Data, pps 227--236, Washington, DC. The postcript copy of the paper can be found here.