DATA MANAGEMENT 1) File StructureFile Structure 2) Physical OrganisationPhysical Organisation 3) Logical OrganisationLogical Organisation 4) File OrganisationFile Organisation Prepared by: Teacher Fina 28 th May 2005, Saturday Lower Sixth Form Computer Studies

File 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. Page 2/12

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 Structure Page 3/12

Information has to be organised so that any item of data can be retrieved when it is needed. File Structure BITSCHARACTERSFIELDSRECORDFILEDATABASE are grouped to form.... which make up.... of data within each.... on a... Several of which may form a Page 4/12

Physical 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. Page 5/12

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 Organisation Page 6/12

Physical Organisation Double 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 Page 7/12 Data entering buffer 1 Data leaving buffer 2

Logical 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 Page 8/12

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 Organisation Page 9/12

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 Organisation Page 10/12

File Organisation Types of File Organisation: (i) SERIAL; (ii) SEQUENTIAL; (iii) INDEXED SEQUENTIAL; (iv) RANDOM Page 11/12

HOMEWORK Make a reasearch-notes on relevant internet resources on those ‘4 types of file organisation’ and submit to me on 2 nd June 2005, Wednesday. File Organisation Page 12/12 THANK YOU FOR YOUR ATTENTION