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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Domain relational calculus ： ウィキペディア英語版 Domain relational calculus In computer science, domain relational calculus (DRC) is a calculus that was introduced by Michel Lacroix and Alain Pirotte as a declarative database query language for the relational data model.〔Michel Lacroix, Alain Pirotte: Domain-Oriented Relational Languages. VLDB 1977: 370-378〕 In DRC, ''queries'' have the form: :$\backslash$ where each Xi is either a domain variable or constant, and $p(\backslash langle\; X\_1,\; X\_2,\; ....,\; X\_n\; \backslash rangle)$ denotes a DRC ''formula''. The result of the query is the set of tuples X1 to Xn which makes the DRC formula true. This language uses the same operators as tuple calculus, the logical connectives ∧ (and), ∨ (or) and ¬ (not). The existential quantifier (∃) and the universal quantifier (∀) can be used to bind the variables. Its computational expressiveness is equivalent to that of Relational algebra.〔E. F. Codd: Relational Completeness of Data Base Sub-languages. In R. Rustin, editor, Data Base Systems. Prentice Hall, 1972〕 ==Examples== Let (A, B, C) mean (Rank, Name, ID) in the Enterprise relation and let (D, E, F) mean (Name, DeptName, ID) in the Department relation Find all captains of the starship USS Enterprise: $\backslash left\backslash \; \backslash \; \backslash land\; \backslash \; A\; =\; \backslash mathrm\; \}\; \backslash \; \backslash right\backslash \}$ In this example, A, B, C denotes both the result set and a set in the table Enterprise. Find names of Enterprise crew members who are in Stellar Cartography: $\backslash begin$ \ } \\ & \land \ \\ & \land \ F = C \ \land \ E = \mathrm \} \\ \end In this example, we're only looking for the name, and that's B. F = C is a requirement, because we need to find Enterprise crew members AND they are in the Stellar Cartography Department. An alternate representation of the previous example would be: $\backslash left\backslash \; \}\; \backslash \; \backslash land\; \backslash \; \}\; \backslash \; \backslash right\backslash \}$ In this example, the value of the requested F domain is directly placed in the formula and the C domain variable is re-used in the query for the existence of a department, since it already holds a crew member's id. Relational Data Model: The Relational model uses relation (table) to represent both entities and relationships among entities. A relation may be visualized as a table. However table is just one of the way, among many, to represent a relation. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Domain relational calculus」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.