DATA MANAGEMENTDATA MANAGEMENT1) File Structure

2) Physical Organisation3) Logical Organisation

4) File Organisation

Prepared by: Teacher Fina

28th May 2005, SaturdayLower Sixth Form Computer Studies

File StructureFile Structure Data is stored in folders. Each folder may contain information. The contents of the folder is a record which contains pieces of information called as fields such as names, address and etc. A file is defined as a collection of records, usually held on a disk.

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A file is used in a broader sense to mean a data structure which could hold. For example:- a source code program written in a high-level language like PASCAL;- a binary file containing executable code;- a bitmapped graphic file;- a word processed letter.

File StructureFile Structure

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Information has to be organised so that any item of data can be retrieved when it is needed.

File StructureFile Structure

BITSBITSCHARACTERSCHARACTERS

FIELDSFIELDSRECORDRECORDFILEFILE

DATABASEDATABASE

are grouped to form....which make up....

of data within each....on a...Several of which mayform a.......

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Physical OrganisationPhysical Organisation Data is held on a disk being organised into physical blocks or physical records. On a disk, a physical block consists of 1 or more sectors. The physical block is read into a buffer. A buffer is a space set aside in memory as a temporary store.

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For example,

when a user issues an instruction to read a particular customer record, the entire block is transferred to memory buffer. OS copies the record requested into a record buffer.

Physical OrganisationPhysical Organisation

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Physical OrganisationPhysical OrganisationDouble buffering is a process of two buffers so that while data is being transferred into 1 buffer from the storage device, the other buffer is being emptied and the records processed

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Data entering buffer 1Data entering buffer 1

Data leaving buffer 2Data leaving buffer 2

Logical OrganisationLogical Organisation Logical Organisation is meant the organisation as perceived by user, who does not need to be aware that the records are held in physical blocks. 2 types of logical organisation: -(i) Fixed length records(ii) Variable length records

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FIXED LENGTH RECORD If the file consists of FIXED length record then every record has exactly the same number of fields and every field contains exactly the same number of bytes.

Logical OrganisationLogical Organisation

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VARIABLE LENGTH RECORD If the file consists of VARIABLE length record then the number of bytes in any particular field may vary from record to record and the number of fields may vary from record to record.

Logical OrganisationLogical Organisation

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File OrganisationFile Organisation

Types of File Organisation:(i) SERIAL;(ii) SEQUENTIAL;(iii) INDEXED SEQUENTIAL;(iv)RANDOM

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HOMEWORK

Make a reasearch-notes on relevant internet resources on those ‘4 types of file organisation’ and submit to me on 2nd June 2005, Wednesday.

File OrganisationFile Organisation

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THANK YOU FOR YOUR ATTENTION