• 1. Chapter 6Data Management 數據管理
    • 2. Data must be carefully control becauseTo get accurate and meaningful result To protect the computer hardware from being damaged
    • 3. Sources of error (錯誤來源)Fill in error (填寫錯誤) Transcription error (抄寫錯誤) Input error (輸入錯誤)
    • 4. How to control? Data verification (數據核對) Data validation (數據驗證)
    • 5. Data verification (數據核對)Display data to let the user check again and ask for confirm Double check Triple check ……. For example : Bill Payment System, Ticket Booking System
    • 6. Data validation (數據驗證)Programmer foresee possible errors and detect them and probably correct them Presence check - This field must be filled? Range check - Data exceed a limit? Type check - Data type match or not? Consistency check - Strange data appear? Control total - total no. of record correct?
    • 7. Data validation (數據驗證)Check digit Can be found in ID card, bar codes, ISBN … Use formula to check the data is correct or not For example : this student ID 1234(0) correct? Formula : Add all digit, Divide the sum by 10, Found the remainder In this case, this is a valid (有效) ID !!
    • 8. Common used checking methodWeighted modulo 11 check Formula : unit digit X 2 tenth digit X 3 hundredth digit X 4 : add all, mod 11, use 11 - the remainder
    • 9. HK ID. No. CheckingA237637(A)X 2X 3X 4X 5X 68141835 14 = 122122 mod 11 = 1check digit = 11 - 1 = 10X 7X 8249++++++It is valid有效!!
    • 10. HK ID. No. CheckingZ297138(0)X 2X 3X 4X 5X 620814543516= 340340 mod 11 = 10check digit = 11 - 10 = 1X 7X 849++++++It is invalid無效!!