Computers14 Ch6
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Computers14 Ch6 Presentation Transcript

  • 1. Storage and Multimedia Chapter 6 B.M.H
  • 2. Index
    • How data is organized
    • How to access the file
      • File organization
        • Sequential file organization
        • Direct file organization
        • Indexed file organization
    • How to process the file
      • Batch processing
      • Transaction processing
  • 3. How data is organized
    • Raw data is organized into
      • Characters
      • Fields
      • Records
      • File
      • Databases
  • 4. How data is organized
    • Characters
      • the smallest element
      • A letter, digit, or special character
    • Fields
      • A set of related characters
    • Records
      • A collection of related fields
  • 5. How data is organized
    • File
      • A collection of related records
    • Databases
      • A collection of interrelated files stored together with minimum redundancy
  • 6. How data is organized
    • Key
      • A field of particular interest
      • A unique identifier for a record
      • Ex. custom number, product number, social security number,
  • 7. The File Plan
    • The plan considered by some computer professional
      • How to access the file
        • File organization
      • How to process the file
  • 8. How to access the file
  • 9. File organization
    • Three major methods of organizing data files in secondary storage
      • Sequential file organization
      • Direct file organization
      • Indexed file organization
  • 10. Sequential File Organization
    • Records are arranged sequentially
      • stored in order according to a key field
    • To find a particular record
      • All the prior records in the file must be read before the desired record is reached
  • 11. Direct File Organization
    • Random file organization
    • Allows direct (random) access
      • The ability to go directly to the desired record by using a record key
    • The benefit
      • the ability to read, change, and return a record to its same place on the disk
      • called updating in place
  • 12. Direct File Organization
    • To find the record on a disk
      • Used a certain formula to apply to the record key
        • Deriving a number to use as the disk address
      • Hashing, or randomizing algorithm
        • The mathematical operation that is applied to a key to yield a number that represents the address
  • 13. Simple Hashing Schemes
    • A general idea of how the process works
  • 14.  
  • 15. Hashing Algorithm
    • Collision
      • For a hashing algorithm to produce the same disk address (called synonym) for two different records
        • Even though the record keys are unique
    • To recover from a collision
      • One way : to use the next available record slot in the disk  fig 6-13
  • 16. Indexed File Organization
    • A compromise between the sequential and direct methods
      • Records are stored in sequential order
      • The file also contains an index
        • The index contain
          • The record key
          • The address associated with the key
  • 17. Storage media
    • Tape storage
      • Limited to sequential file organization
    • Disk storage
      • May be sequential , and also accessed directly
      • a direct-access storage device (DASD)
        • The computer can go directly to the desired record on the disk
  • 18. How to process the file
  • 19. Processing stored data
    • Most business file processing
      • involves processing transactions to update a master file
      • Transaction : a business event that required the business’s records to be updated
        • Ex. a retail sale, the receipt of ordered goods
      • Master file : contains data that must be updated as transactions occur
        • Ex. an inventory file, an employee file, a customer file
  • 20. Processing stored data
    • Two main methods
      • Batch processing
      • Transaction processing
  • 21. Batch processing
    • A technique of processing transaction data in groups at a more convenient later time
      • Transactions are collected into batches
      • to be processed at a time
        • when the computer may have few online users and thus be more accessible, often during the night
    • No direct user interaction
    • Ex. web page club’s member file
  • 22. Batch processing
    • Transaction file
      • Contains all changes to be made to the master file: additions, deletions, and revisions
    • Master file
      • Periodically updated with the changes called for in the transaction file
  • 23. Batch processing
    • Changes are stored in transaction files
    • Transaction file is sorted by a key field
      • All the transactions are in sequential order
      • Ex. By the member number of the webpage club
    • Matching the keys from the mater file and transaction files
      • Records of mater file already are in order
    • CPU processes the appropriate action
    • A newly updated master file is created
  • 24.  
  • 25. Batch processing
    • Advantage
      • Efficiency
    • Disadvantage
      • The master file is current only immediately after processing
  • 26. Transaction processing
    • A technique of processing transactions immediately, as they occur
      • Each transaction is handled immediately
      • Real-time processing
        • A transaction is processed fast enough for the result to come back and be acted upon right away
      • Online :
        • the terminals must be connected directly to the computer
    • Ex. bank withdrawal, flight reservation
  • 27. Transaction processing
    • Use disk storage
      • For direct access to the desired record
    • Advantage
      • Immediate access to stored data
      • Immediate updating of the stored data
  • 28.  
  • 29. Batch & Transaction Processing
    • Numerous computer system
      • combine the best features of both methods of processing
        • Transaction processing : used for activities related to the current needs of people
        • Batch processing : done at any time, even in the middle of the night
  • 30. Batch & Transaction Processing
    • Ex. Store system
      • Updating the individual item’s inventory
        • Needed transaction processing
      • Producing daily and weekly sales report
        • Used batch processing