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MCA5033
Winter
2016
1 What are the different strategies
of OSS licensing? Explain briefly.
Answer: OSS licensing strategies which are
given below:
Ø Expansion
strategy: It is an open
source demonstration of the “law of conservation of modularity” which says that
a single layer of a software stack is "modular and agreeable"
permitting adjacent
2 Explain ACID properties in transaction
management
Answer:
Transactions
In the context of a database, a transaction can be defined as a group of tasks (database operations). It is a unit of a program execution that accesses and possibly modifies various data objects (database tuples, relations). A
In the context of a database, a transaction can be defined as a group of tasks (database operations). It is a unit of a program execution that accesses and possibly modifies various data objects (database tuples, relations). A
3 Explain the SELECT and PROJECT
operations.
Answer: Relational Algebra Operators are
mathematical functions used to retrieve queries by describing a sequence
4 What is a Trigger?
Describe trigger creation in detail.
Answer: SQL trigger is a
set of SQL statements stored in the database catalog and is executed or fired
whenever an event (insert, update or delete) that is associated with a table
occurs. This is a special type of stored procedure which is invoked directly by
an event. The main difference between a trigger and a stored procedure is that
a trigger is called automatically whenever data modification takes place while
the stored procedure must be called explicitly.
The general form of trigger declaration is given below:
CREATE TRIGGER Triggername (BEFORE | AFTER) _table Name_
(INSERT| UPDATE | DELETE)
MySQL stores triggers in data directory with the files named
table name. TRG and triggername.TRN. The tablename. TRG file maps the trigger
to the corresponding table and the trigger name. TRN file contains the trigger definition.
It has some limitations when compared to standard SQL. MySQL
trigger cannot Use SHOW, LOAD DATA, LOAD TABLE, BACKUP DATABASE, RESTORE, FLUSH
and RETURN statements. It cannot use statements that commit or rollback
implicitly or explicitly. And also it cannot use prepared statement such as
PREPARE, EXECUTE because Itcan’t use dynamic SQL.
MySQL trigger cannot call a stored procedure.
Creating Trigger in MySQL
In order to create a trigger we can use CREATE TRIGGER
statement. The syntax of CREATE TRIGGER statement is as follows:
CREATE TRIGGER trigger_name trigger_time trigger_event
ON table_name
FOR EACH ROW
BEGIN
...
END
We are giving the trigger name after the CREATE TRIGGER
statement. The trigger name should follow the naming convention [trigger time]_[table
name]_[trigger event], for example before_employee_update. Trigger activation
time can be either BEFORE or AFTER. We can use BEFORE keyword if we want to
process the action prior to the modification on the table and can use AFTER if
we need to process action after changes are made. Trigger events are INSERT,
UPDATE and DELETE. A trigger should be associated with a specific table.
Without a table trigger would not exist therefore we have to specify the table
name after the ON keyword. SQL is code is placed between BEGIN and END
keywords. Consider, we have an employee table with attributes Ename, empid,
exp, salary. Then we create a new table named Emp_audit. This table is used to keep
the record of changes made to employee table.
CREATE TABLE Emp_audit (
eid int(11) NOT NULL AUTO_INCREMENT,
Name varchar(50) NOT NULL,
Changedon datetime DEFAULT NULL,
actionvarchar (50) DEFAULT NULL,
PRIMARY KEY (eid));
Then, we can create the BEFORE UPDATE trigger to be invoked
before a change is made to the employee records
DELIMITER $$
CREATE TRIGGER before_employee_update
BEFORE UPDATE ON employees
FOR EACH ROW BEGIN
INSERT INTO Emp_audit
SET action = 'update',
eid = OLD.empid,
Name = OLD.Ename,
Changedon = NOW ();
END$$
DELIMITER
5 Write short notes on:
a) Ingres
b) Postgres
c) Postgres95
d) PostgreSQL7
e) PostgreSQL8
Answer: Ingres
Ingres, a research project to create a relational database,
was a project in the early 1970s at the University of California, Berkeley. This
was the starting of the research and later many other databases were developed
from this research and which includes the commercial Ingres and Informix
6 Describe briefly about
the experimental evaluation. Write the significance of generic benchmarks.
Answer: The performance of a database system
can be evaluated with bench marks. Probably the most popular and widely
accepted is TPC-C (it is a benchmark tool by TPC (Transaction processing
Performance
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