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Computers14 Ch6
 

Computers14 Ch6

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    Computers14 Ch6 Computers14 Ch6 Presentation Transcript

    • Storage and Multimedia Chapter 6 B.M.H
    • 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
    • How data is organized
      • Raw data is organized into
        • Characters
        • Fields
        • Records
        • File
        • Databases
    • 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
    • How data is organized
      • File
        • A collection of related records
      • Databases
        • A collection of interrelated files stored together with minimum redundancy
    • How data is organized
      • Key
        • A field of particular interest
        • A unique identifier for a record
        • Ex. custom number, product number, social security number,
    • The File Plan
      • The plan considered by some computer professional
        • How to access the file
          • File organization
        • How to process the file
    • How to access the file
    • File organization
      • Three major methods of organizing data files in secondary storage
        • Sequential file organization
        • Direct file organization
        • Indexed file organization
    • 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
    • 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
    • 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
    • Simple Hashing Schemes
      • A general idea of how the process works
    •  
    • 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
    • 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
    • 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
    • How to process the file
    • 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
    • Processing stored data
      • Two main methods
        • Batch processing
        • Transaction processing
    • 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
    • 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
    • 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
    •  
    • Batch processing
      • Advantage
        • Efficiency
      • Disadvantage
        • The master file is current only immediately after processing
    • 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
    • Transaction processing
      • Use disk storage
        • For direct access to the desired record
      • Advantage
        • Immediate access to stored data
        • Immediate updating of the stored data
    •  
    • 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
    • Batch & Transaction Processing
      • Ex. Store system
        • Updating the individual item’s inventory
          • Needed transaction processing
        • Producing daily and weekly sales report
          • Used batch processing