Horizontal Fragmentation-Horizontal fragmentation groups together the tuples in a relation that are collectively used by the main transactions. A horizontal fragment is produced by specifying a WHERE clause condition that shows a restriction on the tuples in the relation. It can also be described using the Selection operation of the relational algebra.

Example:

Let us demonstrate horizontal fragmentation with the help of an example.

 DEPOSIT (branch-code, account-number, customer-name, balance)

A sample relation instance of the relation DEPOSIT is shown in Figure.

Branch-code	Account number	Customer name	Balance
1101	3050	Suresh	5000
1101	2260	Swami	3360
1102	1170	Swami	2050
1102	4020	Khan	10000
1101	1550	Khan	620
1102	4080	Khan	1123
1102	6390	Khan	7500

                                                              Figure: Sample DEPOSIT relation

Mathematically a fragment may be described as a selection on the global relation R. The reconstruction of the relation R can be taken by taking the union of all fragments.

So let us decay the table in Figure into horizontal fragments. Let us do these fragments on the branch-code as 1101 and 1102

DEPOSIT1 obtained by selection on branch-code as 1101
Branch-code	Account number	Customer name	Balance
1101	3050	Suresh	5000
1101	2260	Swami	3360
1101	1550	Khan	620
DEPOSIT2 obtained by selection on branch- code as 1102
Branch-code	Account number	Customer name	Balance
1102	1770	Swami	2050
1102	4020	Khan	10000
1102	4080	Khan	1123
1102	6390	Khan	7500

                                        Figure: Horizontal fragmentation of relation DEPOSIT

 

The two fragments can be described in relational algebra as:

 

DEPOSIT1 = σ branch-code= 1101 (DEPOSIT)

DEPOSIT2 = σ branch-code= 1102 (DEPOSIT)

These two fragments are given in Figure. Fragment 1 can be stored in the branch whose code is 1101 whereas the second fragment can be stored at branch 1102.

In our example, the fragments are disjoint. Though, by changing the selection predicates used to construct the fragments; we may have overlapping horizontal fragments. This is a type of data replication.

Posted Date: 3/13/2013 8:39:45 AM | Location : United States

Ask an Expert

Related Discussions:- horizontal fragmentation, Assignment Help, Ask Question on horizontal fragmentation, Get Answer, Expert's Help, horizontal fragmentation Discussions

Write discussion on horizontal fragmentation
Your posts are moderated

Write your message here..

Related Questions

Define outer union operation of the relational algebra, Define outer union ... Define outer union operation of the relational algebra. Compute the outer union for the relations R and S given below. Outer Join - If there are any values in one tabl

Writing a pl/sql program, Problem 1. Create a PL/SQL program to insert ... Problem 1. Create a PL/SQL program to insert data into student table and display the details of the student having Reg.No 1010 Writing a PL/SQL program to Insert data

ER-diagram, The State of NewYork certifies firefighters throughout state an... The State of NewYork certifies firefighters throughout state and keep track all of them, as well as of the state’s fire departments. Each fire department has unique department numb

Insert statement reverses storage space and transfers value, A field-groups... A field-groups statement or an insert statement reverses storage space and transfers values. False.

Computing the closure of a set of functional dependency, What is meant by c... What is meant by computing the closure of a set of functional dependency? The closure of F denoted by F + is the set of functional dependencies logically implied by F.

Can a domain, Can a domain, assigned to a data element be changed? Yes.... Can a domain, assigned to a data element be changed? Yes.  We can do so by just overwriting the entry in the field domain.

Case tools, explain at least five widly used case tools explain at least five widly used case tools

Read-set(t) and timestamps-optimistic concurrency contents, read-set(T) : E... read-set(T) : Each data items that are read by a transaction T Timestamps : for all transaction T, the start-time and the end time are reserved for all the three phases.

Explain alternate key, Explain Alternate key? Alternate Key - All the... Explain Alternate key? Alternate Key - All the candidate keys except primary key are known as alternate keys.

single products ordered, For Colorado customers calculate the number of si... For Colorado customers calculate the number of single products ordered. If a product is purchased on multiple orders, it should be counted only single time. The result should conta