Parcial 2

Question 1

Fundamental, Additional, Union Compatibility

Answer 1

Relational Algebra Operators

Question 2

Selection, Projection, Union, Set, Cartessian

Answer 2

Fundamental

Question 3

Intersection, 0-join, Natural join, semijoin, division

Answer 3

Additional

Question 4

Same degree, corresponding attributes

Answer 4

Union compatibility

Question 5

Produces a horizontal subset of the operand relation

Answer 5

Selection

Question 6

Produces vertical slice if a relation

Answer 6

Projection

Question 7

Result contains tuples that are in R or in S, but not both (duplicates removed)
R, S should be union-compatible

Answer 7

Union

Question 8

Result contains all tuples that are in R, but not in S

Answer 8

Set Difference

Question 9

The result of R × S is a relation of degree (k1+ k2) and consists
of all (n1* n2)-tuples where each tuple is a concatenation of one
tuple of R with one tuple of S.

Answer 9

Cartesian

Question 10

Typical set intersection, R, S union-compatible

Answer 10

Intersection

Question 11

There are various forms of join. The
primary classification is between inner join and outer join.

Answer 11

0-Join

Question 12

defined over the set of attributes A, by relation
S, defined over the set of attributes B, is the subset of tuples of R that
participate in the join of R with S.

Answer 12

Semijoin

Question 13

T = R ÷ S gives T of degree k1-k2 [i.e., T(Y) where Y = A-B] such that for a
tuple t to appear in T, the values in t must appear in R in combination with every
tuple in S

Answer 13

Division

Question 14

*Specify the properties that the result should hold
*Tuple relational calculus
*Domain relational calculus

Answer 14

Relational Calculus

Question 15

Query of the form {t|F{t}} where
t is a tuple variable
F is a well-formed formula

Answer 15

Tuple Relational Calculus

Question 16

Query of the form x1, x2, …, xn|F(x1, x2, …, xn) where
F is a well-formed formula in which x1, x2, …, xn are the free variables

Answer 16

Domain Relational Calculus

Question 17

An interconnected
collection of autonomous
computers that are
capable of exchanging
information among
themselves.

Answer 17

Computer network

Question 18

Hosts (nodes, end
systems)
Switches
Communication link

Answer 18

Components

Question 19

Network of networks

Answer 19

Internet

Question 20

WAN, LAN, MAN

Answer 20

Types of networks according to scale

Question 21

✦ Distance between any two nodes > 20km and can go as high as thousands of kms
✦ Long delays due to distance traveled
✦ Heterogeneity of transmission media
✦ Speeds of 150Mbps to 10Gbps (OC192 on the backbone)

Answer 21

WAN

Question 22

✦ Limited in geographic scope (usually < 2km)
✦ Speeds 10-1000 Mbps
✦ Short delays and low noise

Answer 22

LAN

Question 23

In between LAN and WAN

Answer 23

MAN

Question 24

Irregular, Bus, Star, Ring, MESH

Answer 24

Types of networks according to Topology

Question 25

Unicast, multi-point

Answer 25

Communication Schemes

Question 26

One or more (direct or indirect) links between each pair of nodes Communication always between two nodes Receiver and sender are identified by their addresses included in the message header Message may follow one of many links between the sender and receiver using switching or routing

Answer 26

Unicast (Point-to-point)

Question 27

Messages are transmitted over a shared channel and received by all the nodes Each node checks the address and if it not the intended recipient, ignores Multi-cast: special case ✦ Message is sent to a subset of the nodes

Answer 27

Multi-point(Broadcast)

Question 28

Twisted pair *Coaxial *Fiber optic cable *Satellite *Microwave *Wireless

Answer 28

Communication alternatives

Question 29

Header, text. Block Error Check

Answer 29

Packet Format

Question 30

Source addres, Destination addres, Message number, Packet number, Acknowledgment, Control Information

Answer 30

Parts of header

Question 31

Software that ensures error-free, reliable and efficient communication between hosts

Answer 31

Communication Protocols