Explain Distributed Data Base Design ?

Whether the data base is centralized or distributed the design principals & concepts like relational data base model, entity relationship modeling & normalization of data base are still applicable.
Distributed data base design is based on 3 issues:
How to partition the data base in to fragments Which fragments to replicate Where to locate those fragments replicates.
Data fragmentation :
data fragmentation allows you to break a single object in to 2 (or) more segments (or) fragments.
The object may be data base table or any thing.
Each fragment can be stored at any site or over a computer network.
Information about the data fragmentation is stored in the distributed data catalog(DDC).
We have 3 types of data fragmentation's. Horizontal Vertical Mixed
1. Horizontal fragmentation :
Refers to the division of relation in to sub sets of tuples ( rows).
Each fragment has unique rows. The unique rows all have the same attributes(columns).
Each fragments represents a select statement, with the where cause on a single attribute. Cust name Cust address Cust bal Cust due 10 Sasi USA 20,000 1000 11 Sai India 30,000 2000 12 Satya Australia 40,000 3000 13 Sindhu Africa 50,000 4000 14 Sailu India 6,0000 5000
From the above table a company requires information about customers in India, USA countries.
Horizontal fragmentation of customer table by country : Fragment name Location Condition Customer numbers No. of rows Cust –H1 India Cust address=India 11, 14 2 Cust – H2 USA Cust address=USA 10 1
Table name : cust–H1 location India Cust–no Cust–name Cust–address Cust–bal Cust–due 11 Sai India 20,000 2000 14 Sailu India 60, 000 5000
Vertical fragmentation : Division of a relation in to attribute (columns) subsets.
Each fragment is stored at different mode
Each fragment has unique columns.
Which is equivalent to the project statement.
From the above table. The vertical fragmentation as follows: For example the company is divided in to 2– departments like department & collection department.
Each department has an interest in only a few attributes in customer table. Fragment name Location Attribute names Cust–v1 India Cust–num, cust– name, cust– due Cust–v2 USA Cust–num, cust–balance, cust–due
Table name : cust V1 cust – num cust– name cust– due 11 Sai 2000 14 Sailu 5000
Table name : cust V2 Cust–no Cust–name Cust–due 10 Sasi 1000
Mixed fragmentation's :refers to a combination of horizontal and vertical strategies.
Data replication :
Data replication refers to storage of data copies at multiple sites served by a computer network.
Fragment copies can be stored at several sites to serve data availability & response time.
Benefits of data replication : Data availability Data distribution Reduced query cost Back up
Data Allocation :Describe the process of deciding where to locate data
Data allocation strategies are :
1. which centralized the data allocation means entire data base is stored at one & site.
2. with partitioned data allocation means data base is divided in to two (or) more disjoint parts & stored at two (or) more sites.
3. With replicated data allocation means copies.
4. If one (or) more data base fragments are stored in several sites. More data allocation studies focus on which data to locate where.