6) Organisation of data

• What is a fixed-length record?


  Fixed-length records have the same number of bytes in each record and the same number of fields.
• What is a variable length record?

  Variable length records have a different number of bytes in each record or a different number of fields.
• What are the advantages of fixed-length records?

  Fixed-length records are easier to program as we know how much space will be required, Fixed-length records are easier to process by computers as start and end locations are known.
• What are the advantages of variable length records?

  Variable length records save storage space as there is no blank space, variable length records avoid truncation as each field can extend to accommodate any number of characters.
• What is the range check?

  This is to see if the data within a specific range.
• What is the type check?

  This is to see if the data is the right type.
• What is the length check?

  This is to see if the data has the correct number of characters in it.
• What is the format check?

  This is to see if the data follows a certain structure. (LLNN NLL)
• What is the presence check?

  This ensures the data has been entered into the field.
• What is double entry?

  This is where the user enters the data in twice and then a comparison is made against them to ensure they are the same.
• What is proof reading?

  This is when someone reads over the content of the input to manually check it.
• Describe direct (random) access files in terms of hashing algorithms, overflow areas, and the need for files to be re-organized on occasions (6)?

  The physical location of the record is calculated using a hashing algorithm, This calculation is carried out on data in the key field, A data collision occurs when two data items are hashed to the same location, In this case there needs to be an overflow area where the latest data is stored, When there are many items in the overflow area, access may become slow, In which case a new hashing algorithm is required and a larger file may be needed.
• What is a disaster recovery?

  This restores production data to an operational state after a disaster.
• What is operational recovery?

  This restores data in the event of data loss or logical corruption that may occur during routine processing.
• What is archival recovery?

  This preserves transaction records, email and other business work products for regulatory compliance.
• What is archiving?

  Archiving is where you have files of importance that need to be kept so that they can be used again in the future. Archiving allows for the backup of files on an archived system instead of the main system.
• What is generations of files backup?


  This involves the storage of the three most recent versions of the master file, Useful if one version is corrupted because the previous versions are still available, Data should be stored off site in case of a disaster.
• What is incremental backup?


  Only backs up data that has been changed since the last backup and writes over old backups, Useful as it saves storage space, Only allows the user to restore the most recent backup.