| 書(shū)目名稱(chēng) | The Problem of Incomplete Information in Relational Databases | | 編輯 | G?sta Grahne | | 視頻video | http://file.papertrans.cn/918/917696/917696.mp4 | | 叢書(shū)名稱(chēng) | Lecture Notes in Computer Science | | 圖書(shū)封面 |  | | 描述 | In a relational database the information is recorded as rowsin tables. However, in many practical situations theavailable information isincomplete and the values for somecolumns are missing. Yet few existingdatabase managementsystems allow the user to enter null values in thedatabase.This monograph analyses the problems raised by allowing nullvalues in relational databases. The analysis coverssemantical,syntactical, and computational aspects.Algorithms for query evaluation,dependency enforcement andupdates in the presence of null values are alsogiven.The analysis of the computational complexity of thealgorithms suggests that from a practical point of view thedatabase should be storedas Horn tables, which aregeneralizations of ordinary relations, allowing null valuesand Horn clause-like restrictions on these null values. Horntables efficiently support a large class of queries,dependenciesand updates. | | 出版日期 | Book 1991 | | 關(guān)鍵詞 | Abfragenauswertunge; Abh?ngigkeiten; Aktualisierungen; Incomplete Information; Query Evaluation; Relation | | 版次 | 1 | | doi | https://doi.org/10.1007/3-540-54919-6 | | isbn_softcover | 978-3-540-54919-2 | | isbn_ebook | 978-3-540-46507-2Series ISSN 0302-9743 Series E-ISSN 1611-3349 | | issn_series | 0302-9743 | | copyright | Springer-Verlag Berlin Heidelberg 1991 |
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