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Chapter 24: Problem 3

What are the differences among immediate, deferred, and detached execution of active rule actions?

Short Answer

Expert verified
Immediate execution in active rule actions executes the action immediately after the rule is triggered. Deferred execution postpones the execution to the end of the transaction, creating a pending actions queue, maintains database consistency by completing all or none transaction rules. The detached execution sets up a separate new transaction for the action part of a triggered rule decoupled from the original transaction.

Step by step solution

01

Definition of Immediate Execution

The Immediate execution is as shares its name implies, the actions of rules are carried out immediately after the rule is triggered. No transaction queue is created. This type of rule is useful in situations where immediate feedback or action is required after a particular event or condition is met.
02

Definition of Deferred Execution

Deferred execution, as opposed to immediate execution, postpones the execution of actions until the end of the transaction, creating a queue of pending actions. If any part of the transaction fails, all the actions in the queue are rolled back. Therefore, this approach is used if the consistency of the database needs to be ensured, as all or none of the transaction rules will be completed.
03

Definition of Detached Execution

Detached execution, the system responds to an event by conditionally scheduling a transaction to execute the action part of a triggered rule. This type of execution result in a new transaction that is separate from the triggering transaction and is usually used when the actions need to be decoupled from the original transaction and should not affect its processing.
04

Comparing and Contrasting the Executions

Immediate execution acts straight away, ensuring prompt action once the trigger occurs. Deferred execution ensures database consistency by enacting all pending actions at the transaction's end, allowing for rollback if necessary. Detached execution separates rule actions from the original transaction, beneficial when the rule action should not influence the original transaction.

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Most popular questions from this chapter

What are the main differences between tuple versioning and attribute versioning?

Consider the following rules: reachab \(\operatorname{le}(X, Y):-f 7 i g h t(X, Y)\) reachable \((X, Y):-\text { flight }(X, Z), \text { reachab }\rceil e(Z, Y)\) where reachable \((X, Y)\) means that city \(Y\) can be reached from city \(X,\) and f7ight \((\mathrm{X}, \mathrm{Y})\) means that there is a flight to city \(Y\) from city \(\mathrm{X}\) a. Construct fact predicates that describe the following: i. Los Angeles, New York, Chicago, Atlanta, Frankfurt, Paris, Singapore, Sydney are cities. ii. The following flights exist: LA to NY, NY to Atlanta, Atlanta to Frankfurt, Frankfurt to Atlanta, Frankfurt to Singapore, and Singapore to Sydney. (Note: No flight in reverse direction can be automatically assumed.) b. Is the given data cyclic? If so, in what sense? c. Construct a model theoretic interpretation (that is, an interpretation similar to the one shown in Figure 25.3 ) of the above facts and rules. d. Consider the query reachable(AtTanta, Sydney)? How will this query be executed using naive and seminaive evaluation? List the series of steps it will go through. e. Consider the following rule-defined predicates: round-trip-reachable \((X, Y):-\) reachab 7 e \((X, Y),\) reachab 7 e \((Y, X)\) duration \((x, Y, z)\) Draw a predicate dependency graph for the above predicates. (Note: dura\(\operatorname{tion}(X, Y, Z)\) means that you can take a flight from \(X\) to \(Y\) in \(Z\) hours. f. Consider the following query: What cities are reachable in 12 hours from Atlanta? Show how to express it in Datalog. Assume built-in predicates like greater-than \((X, Y) .\) Can this be converted into a relational algebra statement in a straightforward way? Why or why not? g. Consider the predicate population(X,Y) where \(Y\) is the population of city X. Consider the following query: List all possible bindings of the predicate pair \((\mathrm{X}, \mathrm{Y}),\) where \(\mathrm{Y}\) is a city that can be reached in two flights from city \(\mathrm{x}\) which has over 1 million people. Show this query in Datalog. Draw a corre. sponding query tree in relational algebraic terms.

Briefly discuss the consistency and termination problems when designing a set of active rules.

Discuss how time is represented in temporal databases and compare the different time dimensions.

What are the main differences between tuple versioning and attribute versioning?
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