There have been many temporal data models proposed in the literature. Most of them are based on relational models. Despite their popularity as design and analysis tools for information systems, entity-relationship (ER) based temporal data models have not drawn as much attention as those based on relational models. One reason is that most ER-based temporal data models lack an underlying formalism and algebra. If a conceptual model, along with an algebra, is formally defined, we can design a query language that operates on the conceptual model rather than on the implementation model. Also, it can provide a basis for a user-friendly visual query language. In this paper, we present a temporal algebra for an ER-based temporal data model called ITDM (Integrated Temporal Data Model). We define ten algebraic operations and ten temporal aggregate operations. We also define time-series-specific operations.
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