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Copyright © 2004 Pearson Education, Inc.
Chapter 24
Enhanced Data Models
for Advanced
Applications
Copyright © 2004 Pearson Education, Inc.
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 24-3
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 24-4
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 24-5
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 24-6
Generalized Model for Active
DB and Oracle Triggers
 CREATE TRIGGER : trigger name
 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 24-7
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 24-8
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. 24.2 (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 24-9
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 24-10
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 24-11


Design and Implementation
Issues for Active Databases
Condition evaluation = rule consideration
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
–
–
–
2.
3.
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
Deferred consideration : The condition is evaluated at the end of
the transaction that included the triggering event.
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 24-12

Design and Implementation
Issues for Active Databases
Options for the relationship between evaluating the rule
condition and executing the rule action
–


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
–
–

Immediate, deferred, and detached
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 24-13
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 24-14
Examples of Statement-Level
Active Rules in STARBURST
 Events : inserted, deleted, and updated
 INSERTED, DELETED, NEWUPDATED, 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 24-15
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 24-16
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 24-17
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 24-18
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 24-19
Triggers in SQL-99
 Similar to 24.1.1
 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 statementlevel trigger in REFERENCING clause
Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright © 2004 Pearson Education, Inc.
Slide 24-20
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 24-21
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 24-22
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 24-23
Summary
Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright © 2004 Pearson Education, Inc.
Slide 24-24