Database Database


Download 466 b.
bet1/19
Sana14.08.2018
Hajmi466 b.
  1   2   3   4   5   6   7   8   9   ...   19





Database

  • Database

  • Database Management System

    • Software that defines a database, stores the data, supports a query language, produces reports, and creates data entry screens.






Database engine

  • Database engine

    • Storage
    • Retrieval
    • Update
  • Query Processor

  • Data dictionary

  • Utilities

  • Security



















Minimal data redundancy.

  • Minimal data redundancy.

  • Data consistency.

  • Integration of data.

  • Sharing of data.

  • Enforcement of standards.

  • Ease of application development.

  • Uniform security, privacy and integrity.

  • Data independence.



Data is most important

  • Data is most important

    • Data defined first
    • Standard format
  • Access through DBMS

    • Queries, Reports, Forms
    • Application Programs
    • 3GL Interface
  • Data independence

    • Change data definition without changing code
    • Alter code without changing data
    • Move/split data without changing code


Add cell number to employee table

  • Add cell number to employee table

  • Existing reports, queries, code will all run as before with no changes.



Uncontrolled Duplication



Files defined in program





Add to file (e.g.Cell phone)

  • Add to file (e.g.Cell phone)

    • Write code to copy employee file and add empty cell phone slot.
    • Find all programs that use employee file.
      • Modify file definitions.
      • Modify reports (as needed)
      • Recompile, fix new bugs.
  • Easier: Keep two employee files?



Oracle

  • Oracle

  • Informix (Unix)

  • DB2, SQL/DS (IBM)

  • Access (Microsoft)

  • SQL Server (Microsoft +)

  • Many older (Focus, IMS, ...)

  • mySQL

  • ProgresSQL











Numbers

  • Numbers

    • Integers
    • Reals
  • Text

    • Length
    • International
  • Date/Time

  • Images

    • Bitmap
    • Vector
  • Sound

    • Samples
    • MIDI
  • Video



Object Definition--encapsulation.

  • Object Definition--encapsulation.

    • Object Name
    • Properties
    • Methods
  • Most existing DBMS do not handle inheritance.

    • Combine into one table.
    • Use multiple tables and link by primary key.
      • More efficient.
      • Need to add rows to many tables.


Separate inherited classes.

  • Separate inherited classes.

  • Link by primary key.

  • Adding a new customer requires new rows in each table.

  • Definitely need cascade delete.





Abstract data type



  • Do'stlaringiz bilan baham:
  1   2   3   4   5   6   7   8   9   ...   19


Ma'lumotlar bazasi mualliflik huquqi bilan himoyalangan ©fayllar.org 2017
ma'muriyatiga murojaat qiling