Distributed Database Management Systems: Lecture 8

Distributed Database
Management Systems
Lecture # 8


In the previous lecture
• Integrity Rules
• Data Manipulation Languages


In this Lecture
• Derived Relational Algebra
Ops…..
• Relational Calculus


Semi join
• Subset of tuples of R that
participate in join of R with S
R

S
=
F

(RA

A

B

S)


Division
• The division of R with degree r
with S with degree s is the set of
(r-s)-tuples t such that
for all s-tuples u in , the tuple tu is
in R.

R S=
R)

A(R)-

A( A(R) xS)-


eNo
E1
E2
E1
E4

pNo
P1
P1
P3
P2

pName
Bridge
Bridge
Tower
Mosque

pNo pName
P1
Bridge
P3
Tower

budget
11.5m
11.5m
10.2m
9.1m

budget
11.5m
10.2m

R

S


Relational Calculus

• Rather than how to obtain
results, we say what the result
is by specifying relationship
between data
• Based on first-order predicate
logic
• Expressed as
{ t | F(t)}


Find the set of all tuples t such
that F(t) is true, where F
implies the predicate condition.


Atomic Formula
• Tuple-variable membership
expression: specified as R(t) or
R.t
• Conditions
–s[A] Θ t[B]
–S[A] Θ c


SQL
• Language based on Tupleoriented Calculs……?


Example
• Select EMP.eName,

DEP.dName from EMP, DEP
where EMP.dNo = DEP.dNo


Domain Relational Calculus
• Domain variable ranges over
values in a domain and specifies
a tuple
• A query in DRC
x1,x2,….xn|F(x1,….xn)
where F is a wff and Xs are free
variables
• Implementation: QBE


Interface with
Programming Languages


• Tightly Coupled
–Programming Language and
database languages are
merged
• Loosely Coupled
–PL is extended with special
concepts


Summary of DMLs
• Procedural and Non

Procedural
• Relational Algebra
• Relational Calculus


Computer
Networks


A computer network is a
system for communication
between two or more
computers


• Computers are
–Interconnected
–Autonomous
• Networking involves
–Hardware components
–Software components


• Computers are called Nodes,
sites, hosts
• Other equipment at nodes
• Equipment connected via links
and channels

Data
Communication


• Communication links carry
data in form of Digital or
analog signals
• Each channel has a certain
capacity
•
•
•

Modulation and Demodulation
Multiplexing
Mode of Operation


Factors that Matter
• Bandwidth
• Mode of Operation
• Software employed


Header

Text

•Source Address
•Destination Address

•Message Number
•Packet Number
•Acknowledgement
•Control Information

Block Error
Check


Types of
Networks