Copyright © 2004 Pearson Education, Inc.

Chapter 24 Enhanced Data Models for Advanced Applications

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Pearson Education, Inc. Slide 24-3 Active Database Concepts and Triggers Generalized Model for Active Databases and Oracle Triggers Design and Implementation Issues for Active Databases Examples of Statement-Level Active Rules in STARBURST Potential Applications for Active Databases Triggers in SQL-99

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Pearson Education, Inc. Slide 24-4 Generalized Model for Active DB and Oracle Triggers Event-Condition-Action (ECA model) –Event : trigger the rule Usually database update –Condition : determines whether the rule action should be executed No condition – executed once the event occurs With condition – executed only when it is true –Action : usually a sequence of SQL statements

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Pearson Education, Inc. Slide 24-5 Generalized Model for Active DB and Oracle Triggers Example (fig. 24.1) –Assume that null is allowed for DNO –TOTAL_SAL is a derived attribute Events 1.Inserting new employee tuples 2.Changing the salary of existing employees 3.Changing the assignment of existing employees from one department to another 4.Deleting employee tuples

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Pearson Education, Inc. Slide 24-6 Generalized Model for Active DB and Oracle Triggers Condition –WHEN clause represents its condition DNO for new tuple is not null (1) An employee whose salary is changed is currently assigned to a department (2 and 4) No condition, always execute it (3) Action –Defined in PL/SQL block Automatically update TOTAL_SAL (1,2,& 4) Update TOTAL_SAL on the old department and later, the new department

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Pearson Education, Inc. Slide 24-7 Generalized Model for Active DB and Oracle Triggers CREATE TRIGGER : trigger name ruleevents AFTER : the rule will be triggered after the events occur ON : specifies the relation on which the rule is specified FOR EACH ROW : the rule will be triggered once for each row that is affected by event WHEN : specify any conditions checked after the rule is triggered but before the action is executed NEW and OLD

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Pearson Education, Inc. Slide 24-8 Generalized Model for Active DB and Oracle Triggers Examples R1, R2, R3, and R4 Row-level trigger vs. statement-level trigger –Row-level trigger Has FOR EACH ROW keyword The rule is triggered separately for each tuple –Statement-level trigger Doesn’t have FOR EACH ROW keyword The rule would be triggered once for each triggering statement

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Pearson Education, Inc. Slide 24-9 Generalized Model for Active DB and Oracle Triggers For example (statement-level trigger), –UPDATE EMPLOYEE SET SALARY = 1.1 * SALARY WHERE DNO = 5; Another example (See fig (b)) –To check whenever an employee’s salary is greater than the salary of his/her supervisor –We can call external procedure INFORM_SUPERVISOR, which notify the supervisor

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Pearson Education, Inc. Slide Design and Implementation Issues for Active Databases How rules are designed and implemented –In addition to creating rules, activate, deactivate, and drop rules are necessary. –Deactivated rule will not be triggered by the triggering event –The activate command will make the rule active again –The drop command deletes the rule from the system

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Pearson Education, Inc. Slide Design and Implementation Issues for Active Databases When triggered action should be executed –Before, after, or concurrently with the triggering event. Most commercial systems are limited to one or two of the options that we will now discuss

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Pearson Education, Inc. Slide Design and Implementation Issues for Active Databases Condition evaluation = rule consideration event condition Options for how the event is related to the evaluation of the rule’s condition 1.Immediate consideration : the condition is evaluated as part of the same transaction as the triggering event, and is evaluated immediately –Evaluate the condition before executing the triggering event –Evaluate the condition after executing the triggering event –Evaluate the condition instead of executing the triggering event 2.Deferred consideration : The condition is evaluated at the end of the transaction that included the triggering event. 3.Detached consideration : The condition is evaluated as a separate transaction, spawned from the triggering transaction

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Pearson Education, Inc. Slide Design and Implementation Issues for Active Databases conditionaction Options for the relationship between evaluating the rule condition and executing the rule action –Immediate, deferred, and detached Most active systems use the immediate option Oracle –uses the immediate consideration (with before/after option) and immediate execution model. –Row-level rules and statement-level rules STARBURST system uses the deferred consideration –Uses the deferred consideration –Only statement-level rules One of the difficulties that prevent the active rules being widespread is that there are no easy-to-use techniques for designing, writing, and verifying rules. (see fig.24.4)

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Pearson Education, Inc. Slide Examples of Statement-Level Active Rules in STARBURST STARBURST, IBM project, experimental DBMS In STARTBURST, only statement-level rules are allowed (see fig. 24.5) CREATE RULE : rule name ON : the relation on which the rule is specified WHEN : to specify the events IF : to specify any conditions (optional) THEN : to specify the action

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Pearson Education, Inc. Slide Examples of Statement-Level Active Rules in STARBURST Events : inserted, deleted, and updated INSERTED, DELETED, NEW- UPDATED, and OLD-UPDATED are used to refer to 4 transition tables that include –The newly inserted tuples, –The deleted tuples, –The updated tuples after they were updated, –And the updated tuples before they were updated, respectively

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Pearson Education, Inc. Slide Examples of Statement-Level Active Rules in STARBURST In statement-level semantics, since the rule designer only refer to the transition tables as a whole and the rule is triggered only once, so the rule must be different from the row-level semantics For example, because multiple employee tuples may be inserted in a single insert statement, we have to check if at least one of the newly inserted employee tuples is related to a department

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Pearson Education, Inc. Slide Examples of Statement-Level Active Rules in STARBURST In R1S (fig. 24.5) EXISTS (SELECT * FROM INSERTED WHERE DNO IS NOT NULL) WHEN (NEW.DNO IS NOT NULL) Examples in figure 24.5 STARBURST uses deferred consideration, which defer evaluation of condition and execution after the transaction ends

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Pearson Education, Inc. Slide Examples of Statement-Level Active Rules in STARBURST Example (fig. A)

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Pearson Education, Inc. Slide Potential Applications for Active Databases Potential applications of active rules –Notification Monitoring system –Enforce integrity constraints GPA alert and course prerequisites –Business rule Salary of employee can’t exceed that of manager –Maintenance of derived data Maintain the derived attribute TOTAL_SAL

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Pearson Education, Inc. Slide Triggers in SQL-99 Similar to Basic events : INSERT, DELETE, and UPDATE –UPDATE One may specify the attributes to be updated FOR EACH ROW and FOR EACH STATEMENT Can specify particular tuple variable names for the old and new tuples (fig. 24.6) Differences between row-level and statement- level trigger in REFERENCING clause

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Pearson Education, Inc. Slide Temporal Database Concepts Time Representation, Calendars, and Time Dimensions Incorporating Time in Relational Databases Using Tuple Versioning Incorporating Time in Object-Oriented Databases Using Attribute Versioning Temporal Querying Constructs and the TSQL2 Language Time Series Data

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Pearson Education, Inc. Slide Multimedia Databases Introduction to Spatial Database Concepts Introduction to Multimedia Database Concepts

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Pearson Education, Inc. Slide Introduction to Deductive Databases Overview of Deductive Databases Prolog/Datalog Notation Datalog Notation Clausal Form and Horn Clauses Interpretation of Rules Datalog Programs and Their Safety Use the Relational Operations Evaluation of Nonrecursive Datalog Queries

Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Pearson Education, Inc. Slide Summary