lecture 6

Question 1

redundancy

Answer 1

redundancy gives rise to waste of memory ,
update, insert and delete anomalies

Question 2

what is a good database and how to achive it

Answer 2

a good database is that one which has no redudncy and no update, insertion and deletion anomalies

Question 3

how to creat a good schema

Answer 3

in order to design a “good” schema, it is necessary
to represent each concept separately in a distinct
relation

Question 4

how can the concepts represented in a (well-
designed) schema be identified?

Answer 4

it can be found by a key

Question 5

define a constraint

Answer 5

constraint can be defind as the the condition that is given to the database but the conditionmust be valid in real intrest

Question 6

what is ment by legal in database

Answer 6

instant of database which satisfy all the constriants

Question 7

different type of constraint in DBMS

Answer 7

domain constraint: those constriant that tell us about the domain like the grade can not be higher then 30 and can not be less then 18
keys : it is used for unique like all student have unique matricola number
containment of domains: this is used where we need same key in two difffent schema i.e matricola number of student must be same in exam schema