Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

Distributed Database
5
...
CENTRALIZED DATABASE SYSTEM
...
2 FEATURES
5
...
4 ARCHITECTURAL MODELS OF DDBMS

1)CLIENT –SERVER ARCHITECTURE
2) PEER TO PEER ARCHITECTURE
3) MULTI DBMS (MDBS) ARCHITECTURE
5
...
5
...
5
...
6 APPLICATIONS OF DISTRIBUTED DATABASES

5
...
Centralized Database System
Centralized Database

Distributed Database

a)It is a database that is stored, located as well as a)It is a database that consists of multiple
maintained at a single location only
...

b)The data access time in the case of multiple
users is more in a centralized database
...


c) This database provides a uniform and
complete view to the user
...


d) A centralized database is less costly
...


e) In a distributed database, if one database fails
users have access to other databases
...


Apache Cassandra,

Apache HBase
...
2 Features :


Some General features of Database are as follows :

•

Location independency - Data is physically stored at multiple sites and managed by an independent
DDBMS
...
High-level queries are transformed into a query execution plan
for simpler management
...


•

Seamless integration - Databases in a collection usually represent a single logical database, and they
are interconnected
...


•

Transaction processing - Distributed databases incorporate transaction processing, which is a
program including a collection of one or more database operations
...


5
...
The sites have the same
operating system, DDBMS, and data structure, making them easily
manageable
...


Types of Homogeneous Distributed Database
➢

There are two types of homogeneous distributed database −

1
...

They are integrated by a controlling application and use message passing
to share data updates
...


Non-autonomous − Data is distributed across the homogeneous nodes and
a central or master DBMS co-ordinates data updates across the sites
...


•

In the case of a heterogeneous distributed database, a particular
site can be completely unaware of other sites causing limited
cooperation in processing user requests
...


➢

Types of Heterogeneous Distributed Databases

1
...


2
...


- The following diagram shows an example of a heterogeneous
database:

Heterogenous DBMS

5
...


This is a two-level architecture where the functionality is divided into
servers and clients
...


2
...
However, they have
some functions like consistency checking and transaction
management
...
The peers share their resource with other
peers and co-ordinate their activities
...


Global Conceptual Schema − Depicts the global logical view of
data
...


Local Conceptual Schema − Depicts logical data organization at
each site
...


Local Internal Schema − Depicts physical data organization at each
site
...


External Schema − Depicts user view of data
...


➢

This is an integrated database system formed by a collection of two
or more autonomous database systems
...


•

Multi-database Conceptual Level − Depicts integrated multi-database
that comprises of global logical multi-database structure definitions
...


•

Local database View Level − Depicts public view of local data
...


•

Local database Internal Level − Depicts physical data organization at
each site
...
5 Distributed Data Storage Technique:
5
...
1Fragmentation : Horizontal , Vertical , Hybrid
➢

Fragmented
In this design, a table is divided into two or more pieces referred to
as fragments or partitions, and each fragment can be stored at
different sites
...
Moreover,
fragmentation increases parallelism and provides better disaster
recovery
...
e
...


➢

The three fragmentation techniques are −
I
...


Horizontal fragmentation

III
...


Vertical Fragmentation:
a)

Vertical fragmentation refers to the process of decomposing a table
vertically by attributes are columns
...


b)

This is because each site may not need all columns of a table
...


c)

The fragmentation should be in such a manner that we can rebuild a
table from the fragment by taking the natural JOIN operation and to make
it possible we need to include a special attribute called Tuple-id to the
schema
...
And by this, the tuples or
rows can be linked together
...
, an are the attributes of T
T is the table (relation)

For example, for the EMPLOYEE table we have T1 as :
Eno

Ename

Design

101

A

Abc

1

102

B

Abc

2

103

C

Abc

3

104

D

Abc

4

105

E

Abc

5

Tuple_id

For the second
...
Horizontal Fragmentation :
a)

Horizontal fragmentation refers to the process of dividing a table
horizontally by assigning each row or (a group of rows) of relation to
one or more fragments
...
Some of the rows or tuples of the table are placed
in one system and the rest are placed in other systems
...


d)

In relational algebra horizontal fragmentation on table T, can be
represented as follows:
σp(T)

where, σ is relational algebra operator for selection
p is the condition satisfied by a horizontal fragment

For example, consider an EMPLOYEE table (T) :
This EMPLOYEE table can be divided into different fragments like:

EMP 1 = σDep = 1 EMPLOYEE
EMP 2 = σDep = 2 EMPLOYEE

These two fragments are: T1 fragment of Dep

=1

Eno

Ename

Design

Salary

Dep

101

A

Abc

3000

1

102

B

Abc

4000

1

103

C

Abc

5500

2

104

D

Abc

5000

2

105

E

Abc

2000

2

Eno

Ename Design Salary

Dep

101

A

Abc

3000

1

102

B

Abc

4000

1

Similarly, the T2 fragment on the basis of Dep = 2 will be :
Now, here it is possible to get back T as T = T1 ∪ T2 ∪ …
...
Hybrid Fragmentation :
a)

b)
c)

➢
•

•

•

The combination of vertical fragmentation of a table followed by
further horizontal fragmentation of some fragments is called mixed or
hybrid fragmentation
...

In some situations, the horizontal and the vertical fragmentation isn’t
enough to distribute data for some applications and in that
conditions, we need a fragmentation called a mixed fragmentation
...

The second method is to first create a set or group of vertical fragments
and then create horizontal fragments from one or more of the vertical
fragments
...
,an(T))
πa1,a2…
...
5
...

➢ Goals of data replication
a) Data replication is done with an aim to:
•

i
...


ii
...


➢

Types of data replication

There are two types of data replication:
1
...
So there is no
difference between original data and replica
...
Asynchronous replication:
In asynchronous replication, the replica will be modified after commit
is fired on to the database
...


Full Replication
In full replication scheme, the database is available to almost every
location or user in communication network
...


High availability of data, as database is available to almost every
location
...


Faster execution of queries
...


Concurrency control is difficult to achieve in full replication
...


Update operation is slower
...


➢ Advantages of no replication

➢

1
...


2
...


Disadvantages of no replication
1
...


2
...


➢ Partial replication

Partial replication means only some fragments are replicated from the
database
...


•

It is used in multimedia applications
...


•

It is also used in manufacturing control system
...
Databases can be broadly
classified into two types, namely Distributed and Centralized databases
...

A distributed database is like a database that consists of two or more files located
in different computers or sites either on the same network or on an entirely
different network
...

There are two types of distributed databases
...


Homogenous distributed database
...


Heterogeneous distributed database
...
On the other hand, maintaining a Distributed
Database In Dbms is very costly in terms of hardware cost and maintenance
...
V

---