Friday, 27 June 2014

File Organization and its type



It is concern with how the data is stored in the database.It allows the designer to make decisions of how the database is to be implemented whereas the logical DB design is concerned with what data is stored in the database.

It follows 2 steps:-
1.) Translate the global logical data model for target DBMS-It includes operations like designing of base relation ,derived data and design of constraints.
2.) Design physical representation- It includes operations like analysis transaction,selection of file organization,selection of indexes and estimate the disk space requirements.

TYPES OF FILE ORGANIZATION-The various types of file organization are:-
1.) Heap or un-ordered file organization
2.) Hash file organization
3.) Index sequential access method ( ISAM )
4.) B tree or Binary tree
5.) Clustered tables

1.) Heap or un-ordered file organization-It is the simplest type of file organization in which the record are placed in the file in the same order as they are inserted.
1.) For storing bulky data
2.) Traversing in the form of linear search
1.) Time consuming process

2.) Hash File Organization- In this records are not stored sequentially in the file instead a hash function is used to calculate the address of the page in which the record is to be stored.The field on which hash function is calculated is known as hash field and if that field act as a key of the relation then it is known as hash key.
Advantages-Search is easy.
Dis-Advantage- Not possible for finding range of values

3.) Index sequential access method ( ISAM )-Data is organized into records which are composed of fixed length and the records are record sequentially. ISAM is a most versatile storage structure than hashing and it provides better functionality when data is retrieve based up on exact key match, pattern matching or a range of values.

4.) B tree or Binary tree-
a.) It is a data structure used to store large amount of information and in this method secondary storage is used to store the leaf nodes of the tree.
b.) The leaf nodes are the only ones that actually stores data icons.
c.) All other nodes are called index nodes or I nodes and these are used to store the guide values which allows us to traverse a tree structure from the root and arrive at the leaf node containing the data item.
d.)The performance of a B tree does not decreases as the relation is updated.

5.) Clustered tables- Clusteres  are group of one or more tables physically stored together because they same common columns.


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