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Data storage
Data storage
Data storage
Data storage
Data storage
Data storage
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Data storage
Data storage
Data storage
Data storage
Data storage
Data storage
Data storage
Data storage
Data storage
Data storage
Data storage
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Data storage

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This presentation is a description of the essence of file structures and also gives a brief introduction to file structures

This presentation is a description of the essence of file structures and also gives a brief introduction to file structures

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  • 1. AN INTRODUCTION TOFILE STRUCTURES Author: Bhagyashree Shetty 1MS10IS027 Department of ISE MSRIT, Bangalore 1
  • 2. INTRODUCTION File structures was a consequence of the idea of storage devices. The important factors of file structures are: Structuring a file. Searching a file. Processing a file. Sorting a file. The following pages explains the concepts of structuring and searching a file using only the “Diagrammatic approach of teaching “wherein the aspects of file structures are depicted pictorially. The following pages begins with data storage devices wherein the whole idea began and then various topics of file structures regarding structuring and searching using figures. 2
  • 3. DATA STORAGE DEVICES OLD METHODS OF MODERN METHODS OF STORAGE STORAGE 3
  • 4. FILE STRUCTURE FILE STRUCTURES MANAGING DATA IN FILES METHODS FOR METHODS FOR STRUCTURING SEARCHING 4
  • 5. GOAL OF FILE STRUCTURE RELATED TO SPACE SPACE AVOID REDUNDANT COMPRESS DATA DEFRAGMENTATION DATA 5
  • 6. GOAL OF FILE STRUCTURE RELATED TO TIME TIME GET DATA GET DATA GET RELATED IN ONE IN MINIMUM DATA AT ONCE ACCESS ACESSES 6
  • 7. FIRST ASPECT OF FS: STRUCTURING DATA IN FILES METHOD HIERARCHY OF DATA IN FILES FIELD AND RECORD PACKING AND BUFFEREING DATA COMPRESSION IN FILES CHANGE OF NOTATION RUN LENGTH ENCODING MORSE CODING HUFFMAN CODING 7
  • 8. HIERARCHY OF DATA IN FILES I/O BUFFER RECORDS FIELDS 8
  • 9. FIELDS AND RECORD ORGANIZATION 1.FIIXED 1.FIIXED LENGTH LENGTH 2.LENGTH 4.SELF 2.FIXEDINDICATOR FIELDS DESCRIBING COUNT RECORD 4.INDEX 3.DELIMITED 3.DELIMITED 9
  • 10. ORGANIZATION EXAMPLES  FIELDS 1 1 RECORDS Rec 1 rec2 1MS10IS027 ANJU****** CSE rec3 Record 1 22 Record 2 10IMS10IS02704ANJU03CSE Record 33 171MS10IS027$ANJU$CSE17 3 1MS10IS027$ANJU$CSE 1MS10IS028$ANNA$CSE…… …………………………………4USN=1MS10IS027NAME=ANJU BRANCH=CSE 4 1MS10IS027$ANJU$cse$ $01#ims10IS024$asha$ 10
  • 11. DATA COMPRESSION IN FILES Using different notation -use Eg: Bihar –BR Goa-GA look up table Kerala-KL Orissa-OR Run length encoding - Eg: TCGAAAAAGTCTC compress repeated sequence of Compressed: letters TCG#05AGTCTC Eg: A .- B-…C-.-. D-.. E. F..-. Morse coding- using symbols to G-. H… I.. J.- represent data (dots and dashes) Eg: Algorithm will be followed Eg: Reuse deleted space and moving Huffman coding -using entire file to space available greedy technique. Optimizing data storage 11
  • 12. SECOND ASPECT OF FS:SEARCHING DATA IN FILESMETHOD USED:INDEXING INDEXING PRIMARY SECONDARY INDEXING INDEXING 12
  • 13. PRIMARY INDEX INDEX = KEY + ADDRESS IF KEY -> PRIMARY KEY, THEN INDEX-> PRIMARY INDEX OPERATIONS PERFORMED ON INDEXES CREATING NEW INDEX LIST INDEX LIST File Record Key addres ..Record ………… 12 50 … ………… ..Record …. 13 100 ………. 16 300 13
  • 14.  ADDING AN ENTRY TO INDEX LIST STEP 1: File NEW RECORD ..Record … ..Record ………. INDEX LIST STEP 2: Key addres 12 50 13 100 KEY AND ADDRESS OF 15 200 PUSH DOWN NEW RECORD 16 300 :DELETING AN ENTRY FROM INDEX LIST INDEX LIST STEP 1: STEP 2: Key addres RECORD TO BE File RECORD ..Record 12 50 DELETED … 13 100 ..Record ………. 15 200 PUSH 16 300 DOWN 14
  • 15.  EDITING AN ENTRY TO INDEX LIST WHEN KEY IS MODIFIED(DELETION FOLLOWED BY INSERTION) File File RECORD ..Record RECORD ..Record … WITH NEW VALUE … ..Record ..Record ………. ………. INDEX LIST INDEX LIST Key addres Key addres 12 50 12 50 RECORD 13 100 RECORD 13 150 IS DELETED IWITH NEW VALUE 15 200 PUSH IS INSERTED 15 200 16 300 DOWN 16 300 SEARCHING PRIMARY INDEX Key addres Key addres File EXTRACT ..RecordSEARCH 12 50 12 50 GO TO … 13 150 ADDRESS 13 150 THE ..RecordKEY ADDRES ………. 15 200 OF REQD 15 200 16 300 KEY 16 300 15
  • 16. SECONDARY INDEX INITIAL SECONDARY INDEX IF KEY ->NON PRIMARY KEY, THEN INDEX-> SECONDARY KEY ADDRES ADRS INDEX CREATING NEW INDEX LIST BT123 100 100 METHOD 1: BT266 222 222 IT205 652 652 File Record ..Record ………… BT347 900 900 … ………… CS111 1200 ..Record …. 1000 ………. PROBLEM: NUMBER OF REFERENCE AGAINST SINGLE NAME METHOD 2 : IMPROVED SECONDARY INDEX ALI IT205 BEN BT347 BT266 BT123 16
  • 17. PROBLEM WITH METHOD 2:NOPLACE TO ACCOMMODATE MORE THAN 3RECORDS WITH SAME NAME METHOD 3 : IMPROVED SECONDARY INDEX-USING LINKED LIST 17
  • 18.  ADDING AN ENTRY TO INDEX LIST KEY ADDRES File BT123 100 NEW ..Record ID BT266 222 RECORD … ..Record ADDR IT205 652 ………. PUSH DOWN NAME IS222 700 BT347 900 CS111 1200 KEY ID BEN BT123 BEN BT266 ALI IT205 SIA IS222 PUSH DOWN BEN BT347 TIA CS111Modification of data in secondary index is same as primary wherein old data is firstdeleted and then the newer one is inserted in same place 18
  • 19. SEARCHING THE SECONDARY INDEX SEARCH KEY ID KEY ID BEN EXTRACT FOR NAME BT123 BEN BEN BT123 BT266 NAME BEN ALI BT266 SIA IT205 IS222 READ NEXT ALI SIA IT205 BEN NAME IS222 BT347 BEN TIA BT347 CS111 TIA CS111 IF NEXT NAME = NAME IF NEXT NAME != NAME DISPLAY MESSAGE AND QUIT This method is followed because secondary index is not unique 19
  • 20. CONCLUSION Using the approach of file structures for storing and managing data, has been depicted here, and ultimately it is the usability and the environment wherein it finds its place. 20

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