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Abstract : |
We present a novel language for querying object-oriented databases. The language is built around the idea of extended path expressions that substantially generalize [ZAN83], and on an adaptation of the first-order formalization of object-oriented languages from [KW89, KLW90, KW92]. The language incorporates features not found in earlier proposals; it is easier to use and has greater expressive power. Some of the salient features of our language are: ffl Precise model-theoretic semantics. ffl A very expressive form of path expressions that not only can do joins, selections and unnesting, but can also be used to explore the database schema. ffl Views can be defined and manipulated in a much more uniform way than in other proposals. ffl Database schema can be explored in the very same language that is used to retrieve data. Unlike in relational languages, the user needs not know anything about the system tables that store schema information. ffl The notions of a type and type-correctness have precise meaning. It accommodates a wide variety of queries that might be deemed well- or ill-typed under different circumstances. In particular, we show that there is more than one way of settling the issue of type correctness. For expository purposes and due to space limitation, we chose to make a number of simplifying assumptions and left some features out. A more complete account can be found in [KSK92]., |
