| 摘要 |
Embodiments of the present invention generally provide methods systems and articles of manufacture for query processing and for constructing a database abstraction model over an underlying physical database. The database abstraction model allows users to compose an abstract query using a logical view of data, instead of using the view of the underlying database architecture. Embodiments of the invention constrain the results returned from processing an abstract query according to relationships that exist for a group of logical fields. First, a group of logical fields may be related because they are part of a logical set. Field-to-field join constraints specify the logical fields that form a set, and an instance indicator used to determine the particular instance of a set that an element of data belongs to, according to a discrimination rule. Second, logical fields may be related because they are part of a series, and an instance identifier may provide an ordering rule used to determine the order of data elements that form the series.
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