A temporal query language for a conceptual model
This chapter was a summary of our work in temporal conceptual models and query languages [173, 178, 174, 179], Our model distinguishes between conceptual and temporal objects, and characterizes the properties of entities (conceptual objects), entity roles (temporal objects), and (temporal and non-temporal) attributes. It also defines temporal constraints among entity roles, differentiates between temporal and conceptual relationships, and provides rules for preserving temporal integrity constraints.
The query language is a temporal extension of GORDAS [177, 176, 178], The temporal query language derives its power from the distinction between temporal and conceptual objects/relationships. It provides natural and high level temporal element constructor operators that simplify temporal query expressions. These operators utilize the entity existence times and the role lifespans in query formulations, without having to refer explicitly to time values. They also use the concepts of boolean conditions, true-times, and temporal projections .
Our query language allows temporal element constructor operators to be defined over entities, entity roles and temporal attributes. It supports temporal version restriction operators and allows multiple temporal scopes in a temporal projection. In addition, the concept of CONTINUOUS and DISCONTINUED temporal elements can be used to specify conditions such as ALWAYS and SOMETIME from temporal logic.
KeywordsQuery Language Entity Type Existence Time Conceptual Object Temporal Element
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