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← Whats a Database - Intro to Relational Databases

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Showing Revision 4 created 05/25/2016 by Udacity Robot.

  1. When you've written code before, you've
    used data structures such as variables,
  2. lists, dictionaries, and objects.
  3. These all let you store information
    while your program is running.
  4. You can build up a complex data
    structure like a list of dictionaries of
  5. objects, and when your program exits,
    that structure will be gone from memory.
  6. You've probably worked with files, for
  7. instance, the files
    containing your own code.
  8. If you edit code in a text editor and
    save it, then quit the editor,
  9. your code doesn't vanish the way
    a variable does, when the program exits.
  10. The file is persistent, or
  11. durable, whereas in memory data
    is ephemeral, or temporary.
  12. Programs can read and write files just
    fine, so why bother with databases?
  13. Well, there are several different
    kinds of databases, but
  14. what they all have in common is
    that they give us both persistence,
  15. like a file, as well as data structures
    for storing and searching our data,
  16. usually much faster and
    easier than we could search a flat file.
  17. They also make it possible for multiple
    programs or users to access, and
  18. modify data at the same time without
    stepping on each other's toes, or
  19. accidentally undoing
    each other's changes.
  20. That's generally not
    possible with flat files.
  21. If two programs write a new version
    of a file at the same time,
  22. then one will overwrite the other.
  23. So these other sorts of
    databases do all that, but
  24. relational databases do even more.
  25. Aside from storing your data,
    relational databases also offer very
  26. flexible tools for
    querying and summarizing data.
  27. If we're doing comparisons, and
  28. if we're drawing connections between
    related pieces of information.
  29. They also let us set up constraints
    which are rules to ensure the changes to
  30. our data are consistent.
  31. We'll see more about those
    later in the course.
  32. Now, let's see how relational
    data bases store data.