A wide range of database applications manage information that varies over time. Many of the underlying database schemas of these were designed using one of the several versions of the Entity-Relationship (ER) model. In the research community as well as in industry, it is common knowledge that the temporal aspects of the mini-world are pervasive and important, but are also difficult to capture using the ER model. Not surprisingly, several enhancements to the ER model have been proposed in an attempt to more naturally and elegantly support the modeling of temporal aspects of information. Common to most of the existing temporally extended ER models is that the semantics of the models are unclear. This problem is addressed in this paper by developing a formal semantics for the TimeER model based on denotational semantics.