v Chapter 6: Integrity and Security 究性与安全性) Domain Constraints(域约束) Referential Integrity(参照完整性) Assertions(断言) Triggers(触发器) Security(安全性) Authorization(授权) Authorization in SQL(SQL中的授权) 标 Database System Concepts 6.1 @Silberschatz, Korth and Sudarshan
Database System Concepts 6.1 ©Silberschatz, Korth and Sudarshan Chapter 6: Integrity and Security （完整性与安全性） Domain Constraints（域约束） Referential Integrity（参照完整性） Assertions（断言） Triggers（触发器） Security（安全性） Authorization （授权） Authorization in SQL（SQL中的授权）
Domain constraints Integrity constraints guard against accidental damage to the database, by ensuring that authorized changes to the database do not result in a loss of data consistency Domain constraints are the most elementary form of integrity constraint They test values inserted in the database, and test queries to ensure that the comparisons make sense New domains can be created from existing data types E.g. create domain Dollars numeric(12, 2) create domain Pounds numeric (12, 2) We cannot assign or compare a value of type dollars to a value of type Pounds However, we can convert type as below (cast rA as Pounds) Database System Concepts 6.2 OSilberschatz. Korth and Sudarshan
Database System Concepts 6.2 ©Silberschatz, Korth and Sudarshan Domain Constraints Integrity constraints guard against accidental damage to the database, by ensuring that authorized changes to the database do not result in a loss of data consistency. Domain constraints are the most elementary form of integrity constraint. They test values inserted in the database, and test queries to ensure that the comparisons make sense. New domains can be created from existing data types E.g. create domain Dollars numeric(12, 2) create domain Pounds numeric(12,2) We cannot assign or compare a value of type Dollars to a value of type Pounds. However, we can convert type as below (cast r.A as Pounds)
Domain Constraints(Cont The check clause in SQl permits domains to be restricted Use check clause to ensure that an hourly-wage domain allows only values greater than a specified value create domain hourly-wage numeric(5, 2) constraint value-test check(value>=4.00) The domain has a constraint that ensures that the hourly-wage is greater than 4.00 The clause constraint value-test is optional; useful to indicate which constraint an update violated Can have complex conditions in domain check create domain Account Type char (10) constraint account-type-test check(value in( Checking,, Saving)) check(branch-name in(select branch-name from branch) Database System Concepts 6.3 @Silberschatz, Korth and Sudarshan
Database System Concepts 6.3 ©Silberschatz, Korth and Sudarshan Domain Constraints (Cont.) The check clause in SQL permits domains to be restricted: Use check clause to ensure that an hourly-wage domain allows only values greater than a specified value. create domain hourly-wage numeric(5,2) constraint value-test check(value > = 4.00) The domain has a constraint that ensures that the hourly-wage is greater than 4.00 The clause constraint value-test is optional; useful to indicate which constraint an update violated. Can have complex conditions in domain check create domain AccountType char(10) constraint account-type-test check (value in (‘Checking’, ‘Saving’)) check (branch-name in (select branch-name from branch))
Referential Integrity Ensures that a value that appears in one relation for a given set of attributes also appears for a certain set of attributes in another relation Example: If Perryridge" is a branch name appearing in one of the tuples in the account relation, then there exists a tuple in the branch relation for branch Perryridge Formal Definition Let M,(R) and r2(R2) be relations with primary keys K, and K2 respectively The subset a of R2 is a foreign key referencing K, in relation r,, if for every t2 in r2 there must be a tuple ty, in such that t,]=t2[a] Referential integrity constraint also called subset dependency since its can be written as hsa(2)∈Ikr(r 6. OSilberschatz. Korth and Sudarshan
Database System Concepts 6.4 ©Silberschatz, Korth and Sudarshan Referential Integrity Ensures that a value that appears in one relation for a given set of attributes also appears for a certain set of attributes in another relation. Example: If “Perryridge” is a branch name appearing in one of the tuples in the account relation, then there exists a tuple in the branch relation for branch “Perryridge”. Formal Definition Let r1 (R1 ) and r2 (R2 ) be relations with primary keys K1 and K2 respectively. The subset of R2 is a foreign key referencing K1 in relation r1 , if for every t2 in r2 there must be a tuple t1 in r1 such that t1 [K1 ] = t2 []. Referential integrity constraint also called subset dependency since its can be written as (r2 ) K1 (r1 )
Referential Integrity in the E-R Model Consider relationship set R between entity sets E, and E2. The relational schema for R includes the primary keys K, of E1 and K2 of e2 Then K, and K2 form foreign keys on the relational schemas for E, and E2 respectively E1 R E2 Weak entity sets are also a source of referential ntegrity constraints For the relation schema for a weak entity set must include the primary key attributes of the entity set on which it depends Database System Concepts 6.5 @Silberschatz, Korth and Sudarshan
Database System Concepts 6.5 ©Silberschatz, Korth and Sudarshan Referential Integrity in the E-R Model Consider relationship set R between entity sets E1 and E2 . The relational schema for R includes the primary keys K1 of E1 and K2 of E2 . Then K1 and K2 form foreign keys on the relational schemas for E1 and E2 respectively. Weak entity sets are also a source of referential integrity constraints. For the relation schema for a weak entity set must include the primary key attributes of the entity set on which it depends E1 R E2