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Lecture Database system concepts - Chapter 5: Other relational languages

In this chapter we study two additional relational languages, QBE and Datalog. QBE, based on the domain relational calculus, forms the basis for query languages sup-ported by a large number of database systems designed for personal computers, such as Microsoft Access, FoxPro, etc. | Chapter 5: Other Relational Languages Database System Concepts, 5th Ed. ©Silberschatz, Korth and Sudarshan See www.db­book.com for conditions on re­use Chapter 5: Other Relational Languages s Tuple Relational Calculus s Domain Relational Calculus s Query­by­Example (QBE) s Datalog Database System Concepts , 5th Ed., Aug 2005 5. ©Silberschatz, Korth and Sudarshan Tuple Relational Calculus s A nonprocedural query language, where each query is of the form {t | P (t ) } s It is the set of all tuples t such that predicate P is true for t s t is a tuple variable, t [A ] denotes the value of tuple t on attribute A s t ∈ r denotes that tuple t is in relation r s P is a formula similar to that of the predicate calculus Database System Concepts , 5th Ed., Aug 2005 5. ©Silberschatz, Korth and Sudarshan Predicate Calculus Formula 1. Set of attributes and constants 2. Set of comparison operators: (e.g., , ≥) 3. Set of connectives: and (∧), or (v)‚ not (¬) 4. Implication (⇒): x ⇒ y, if x if true, then y is true x ⇒ y ≡ ¬x v y 5. Set of quantifiers: ∃ t ∈ r (Q (t )) ≡ ”there exists” a tuple in t in relation r such that predicate Q (t ) is true ∀t ∈ r (Q (t )) ≡ Q is true “for all” tuples t in relation r Database System Concepts , 5th Ed., Aug 2005 5. ©Silberschatz, Korth and Sudarshan Banking Example s branch (branch_name, branch_city, assets ) s customer (customer_name, customer_street, customer_city ) s account (account_number, branch_name, balance ) s loan (loan_number, branch_name, amount ) s depositor (customer_name, account_number ) s .