DBI202 - Part 6

All of the others

3NFconcept is related to (choose 1 answer only): a. Atomic definition b. Full dependency definition c. Transitive dependency definition d. Super Key definition

data model

A ___ is a notation for describing the structure of the data in a database, along with the constraints on that data

DBMS

A ____ is a powerful tool for creating and managing large amounts of data efficiently and allowing it to persist over long periods of time, safely

Nested

A ____ table is a table that is embedded within another table

Collation

A _____ specifies which characters are "less than" which other characters

semi-structured

A database of _____ data model is a collection of nodes, each node is either a leaf or interior

"Consistent" means that: Transactions must not violate any integrity constraints during its execution

A database transaction, by definition, must be ACID (atomic, consistent, isolated and durable). What does "Consistent" mean?

"Isolated" means that: how/when the changes made by one operation in one transaction become visible to other concurrent operations in other transactions

A database transaction, by definition, must be ACID (atomic, consistent, isolated and durable). What does "Isolated" mean?

have either a matching value in the referring (primary) table OR be NULL

A foreign key must

Comparisons between two null values, or between a NULL and any other value, return unknown

Choose one correct statement:

In SQL Server, every DML operation is a transaction regardless of whether it has a BEGIN TRANSACTION or not

Choose the in-correct statement:

All of the others

Choose the most correct statement. Database is created and maintained by a DMBS Database is a collection of data that is managed by a DBMS Database is a collection of information that exists over a long period of time

20

Column A of a relation has the following list of values in the six rows of the table: NULL, NULL, 10, 10, 20, 30 In SQL Server, which of the following is the correct value of AVG(DISTINCT A)?

H has a tuple (3, 5)

Consider the Datalog rule H(x,y) <- S(x, y) AND x > 2 AND y < 6. Relation S(x, y) has 3 tuples (2, 3), (3, 5), and (4, 6). What is about H?

False

Consider the law, that holds for set relations: T intersect(R union S) = (T intersect R) union (T intersect S) The above law still hold for bag relations?

False b

Consider the law, that holds for set relations:(S intersect T) - R = S intersect (T - R).The above law still hold for bag relations?

"_" represents exactly 1 character

Pay attention to the following query:SELECT * FROM R WHERE A LIKE '%_%'; So, in the above case, the wildcard "_" represents what?

We should decompose relation to eliminate anomalies

How to eliminate anomalies when we design a database?

binary relationship

In UML, a _____ between classes is called an association

In composition, when the owning object is destroyed, so are the contained objects. In aggregation, this is not necessarily true.

In UML, what is the difference between an aggregation and a composition?

R is in 2NF

Let R(A,B,C,D) with the following FDs: {AB->C, AC->B, AD->C} Choose a correct statement about R:

(a) and (b) are correct

Look at the following statements:(a)We should pick the right kind of elements (b) When an entity has no non-primary key attribute, we should convert that entity to an attribute (c) Use weak entities when-ever possible (d) Always make redundancies

4

Suppose R is a relation with attributes A1, A2, A3, A4. The only key of R is {A1, A2}. So, how many super-keys do R have?

Selects all customers from table Sales that have made more than 5 orders.

Suppose relation R(a,b,c) has the following tuples: Which tuple is contained in the result of the following query:

w <= x+y

Suppose that tuple t appears, respectively, x, y, and z times in the relations X, Y, and Z. Let t appear w times in the relation: X union (Y intersect Z).Which of the following inequalities is true ?

6

Suppose the relation S(B,C,D) has tuples:Compute the result of the following query: SELECT SUM(D) FROM S WHERE D < 8 AND D > 5

Determines if a value matches any of the values in a list or a sub-query

The IN SQL keyword

Specifies a range to test.

The SQL BETWEEN operator:

a. (a) and (c) are true

The benefits of stored procedures are: (a)They improve the security by letting the admin to LIMIT the access rights of users (b) They can save a lot of storage space (c) They can be reused many times (d) They can store a part of the database in order to retrieve the data more quickly

Association

The binary relationship between classes in UML is called ...

R is in 3NF

The relation R(ABCD) has following FDs: {ACD -> B ; AC -> D ; D -> C ; AC -> B} Choose the correct statement about R:

(4,4)

The table Arc(x,y) currently has the following tuples (note there are duplicates): SELECT x, COUNT(y)FROM Arc GROUP BY x; Which of the following tuples is in the result?

There is an error

The table R(X,Y) currently has the following tuples (note there are duplicates).The relation S(A,B,C) has the following tuples: Which is the result when we execute the following query:

ALTER TABLE

To update a relation's schema, which one of the following statements can be used?

Indexes

Well-designed ____ can reduce disk I/O operations and consume fewer system resources therefore improving query performance

'join' used to connect two or more tables logically with or without common field(s)

What is a "join"?

A key attribute is an attribute that belongs to one of the keys of the relation

What is a key attribute in a relation?

A table can have more than one UNIQUE KEY constraint but only one PRIMARY KEY

What is difference between PRIMARY KEY and UNIQUE KEY ?

A hierarchical data model is a data model in which the data is organized into a tree-like structure

What is the hierarchical data model?

All of the others c

When we apply set operators (UNION, INTERSECT, EXCEPT) to two relations R and S, which conditions on R and S must be satisfied? a. R and S must have schemas with identical sets of attributes and the types (domains) for each attributes must be the same in R and S b. Before we compute the set-theoretic union, intersection, or difference of sets of tuples, the columns of R and S must be ordered so that the order of attributes is the same for both relations

For any relation schema, there is a dependency-preserving decomposition into 3NF

Which of the following statements is correct?

d. All of the others

Which of the following statements is the most correct? a. Using Stored procedures reduces network traffic b. Using Stored procedures improves security c. Using Stored procedures improves performance

All of the others. d

Which of the following statements is true? a. BCNF condition guarantees the non existence of the anomalies. b. In BCNF condition, the left side of every non trivial FD must be a super key. c. Any two-attribute relation is in BCNF.

ALTER TABLE

Which one of the following is NOT a DML command?

Because the intersection operator can be expressed through the union operator and the difference operator

Why the intersection operator is not called a primitive relational algebra operator?