3. (a) Please define what a “trigger” is. If your answer is from the textbook, p

Question

3.

(a) Please define what a “trigger” is. If your answer is from the textbook, please state which page of the textbook from which you got the definition. If your answer is not from the textbook, please also include the complete reference.

(b) Please define what “PL/SQL” is. If your answer is from the textbook, please state which page of the textbook from which you got the definition. If your answer is not from the textbook, please also include the complete reference.

(c) Please define what a “transaction” is. If your answer is from the textbook, please state which page of the textbook from which you got the definition. If your answer is not from the textbook, please also include the complete reference.

(d) Please define “concurrency control” in database operations. If your answer is from the textbook, please state which page of the textbook from which you got the definition. If your answer is not from the textbook, please also include the complete reference.

Explanation / Answer

Trigger:

1. Trigger is SQL procedure that initiates an action when an event occurs.
2. Event means Insert, Deleter or update.
3. Triggers are event driven specialized procedures.
4. Triggers are stored and managed by DBMS.
5. Triggers are cannot be called or executed.

PL/SQL:

1. PL/SQL is a procdural language extension to structured query language.

2. Main purpose is to combine database language and procedural progamming language.

3. Basic unit of PL/SQL is block and it is made up of three parts

a. Declarative part

b. Executable Part

c. Exception building part

transaction:

1. Transaction is defined as group of tasks

2. It is sequence of operation performed as single logical unit of work

3. Transaction have four properties

a. Atomicity

b. Consistency

c. Isolation

d. Durability

concurrency control:

1. In multiprogramming environment, they will be multiple transactions executed simultaneously, It is highly important to control the concurrency of tranactions.

2. While concurrency control protocols should ensure atomicity, isolation,and serializability of transaction

3. They are two categories concurrency control protocols

a. Lock based protocols

b. Time stamp based protocols

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