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Information Systems & Semantic Web University of Koblenz Landau, Germany Advanced Data Modeling Relational Data Model continued Steffen Staab with Simon Schenk TexPoint fonts used in EMF. Read the TexPoint manual before you delete this box.: A A AAA

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ISWeb - Information Systems & Semantic Web Steffen Staab Overview Relational algebra, named perspective Aggregates and grouping SQL Integrity constraints

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ISWeb - Information Systems & Semantic Web Steffen Staab Constant { { a 1 = v 11, …, a n = v 1n }, … …… { a 1 = v k1, …, a n = v kn } }

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ISWeb - Information Systems & Semantic Web Steffen Staab Union Let R1, R2 be relations with the same attributes. R1 [ R2 = { t | t 2 R 1 or t 2 R 2 }

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ISWeb - Information Systems & Semantic Web Steffen Staab Union, example AB ® 1 ® 2 ¯ 1 AB ® 1 ® 2 ¯ 1 ¯ 3 AB ® 2 ¯ 3 R1R1 R2R2 R 1 [ R 2

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ISWeb - Information Systems & Semantic Web Steffen Staab Renaming Let R be a relation whose set of attributes is a 1,…,a n, c 1,…,c m Let b 1, …, b n be distinct attributes such that {b 1, …, b n } Å { c 1, …, c m } = ; Then ½ a 1 ! b 1, …, a n ! b n (R) = {{b 1 = v 1, …, b n =v n, c 1 =w 1, …, c m =w m } | {a 1 = v 1, …, a n =v n, c 1 =w 1, …, c m =w m } 2 R}

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ISWeb - Information Systems & Semantic Web Steffen Staab Set difference Let R 1, R 2 be relatations with the same attributes. R 1 – R 2 = { t | t 2 R 1 and t R 2 }

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ISWeb - Information Systems & Semantic Web Steffen Staab Set difference, example AB ® 1 ® 2 ¯ 1 AB ® 1 ¯ 1 AB ® 2 ¯ 3 R1R1 R2R2 R 1 - R 2

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ISWeb - Information Systems & Semantic Web Steffen Staab SQL SQL is based on set and relational operations with certain modifications and enhancements A typical SQL query has the form: select a_1, …, a_n from R_1, …, R_m where P This query is equivalent to relational algebra expression: ¼ a 1,…, a n ( ¾ P (R 1 £ … £ R m )) The result of an SQL query is a relation. Exceptions?

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ISWeb - Information Systems & Semantic Web Steffen Staab Integrity constraints Domain constraints. Key constraints. Foreign key constraints. More general, defined constraints.

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ISWeb - Information Systems & Semantic Web Steffen Staab Query language Allow one to define: Relation and database schemas; Relations through our relations; Integrity constraints; Updates.

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