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Tuple-generating Dependencies
In relational database theory, a tuple-generating dependency (TGD) is a certain kind of constraint on a relational database. It is a subclass of the class of Embedded dependency, embedded dependencies (EDs). An algorithm known as Chase (algorithm), the chase takes as input an instance that may or may not satisfy a set of TGDs (or more generally EDs) and, if it terminates (which is a priori undecidable), outputs an instance that does satisfy the TGDs. Definition A tuple-generating dependency is a Sentence (logic), sentence in first-order logic of the form: :\forall x_1,\ldots, x_n . \phi(x_1, \ldots, x_n) \rightarrow \exists y_1, \ldots, y_m, \psi(x_1, \ldots, x_n, y_1, \ldots, y_m) where \phi is a possibly empty and \psi is a non-empty Logical conjunction, conjunction of atomic formula, relational atoms. A relational atom has the form R(w_1, \ldots, w_h), where each of the Term (logic), terms w, \ldots, w_h are Variable (mathematics), variables or constants. Fragments Several f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Database Theory
Database theory encapsulates a broad range of topics related to the study and research of the theoretical realm of databases and database management systems. Theoretical aspects of data management include, among other areas, the foundations of query languages, computational complexity and expressive power of queries, finite model theory, database design theory, dependency theory, foundations of concurrency control and database recovery, deductive databases, temporal and spatial databases, real-time databases, managing uncertain data and probabilistic databases, and Web data. Most research work has traditionally been based on the relational model, since this model is usually considered the simplest and most foundational model of interest. Corresponding results for other data models, such as object-oriented or semi-structured models, or, more recently, graph data models and XML, are often derivable from those for the relational model. A central focus of database theory is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |