TEMPORAL MODULES - AN APPROACH TOWARD FEDERATED TEMPORAL DATABASES

In a federated database environment, different constituents of the fed eration may use different temporal models or physical representations for the temporal information. This paper introduces a new concept, cal led a temporal module, to resolve these mismatches among the constitue nts. Intuitively, a temporal module hides the implementation details o f a temporal relation by exposing its information only through two win dowing functions: one function associates each time point to a set of tuples and the other function links each tuple with a set of time poin ts. A calculus-style language is given to form queries on temporal mod ules. Temporal modules are then extended to resolve another type of mi smatch among the constituents of a federation, namely, the mismatch in volving different time units (e.g., month, week, and day) used in reco rding temporal information. Our solution to this mismatch relies on '' information conversions'' provided by each constituent. Specifically, a temporal module is extended to provide several conversion functions; each converts its information to a different time unit. The first ste p to process a query addressed to the federation is to select suitable conversion functions from the extended temporal modules. In order to do so, time units are formally defined and studied. A federated tempor al database model and its query language are proposed. The query langu age is an extension of the calculus-style language above.