Final Exam Review Spring 2004: Applying your knowledge


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Final Exam Review Spring 2004: Applying your knowledge

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Questions and Answers?

1. because the program she is using uses special algorithms.

b. because she highlighted those pixels with her mouse?

II. this means that the domain name server, which translates domain names into IP addresses, was down.

III. with large websites, sometimes it is necessary to store information in large databases, and then when the user needs that information, the website will query the database and retrieve the information. But if the database is down, then the website cannot display the page.

On (I) – you do know the algorithm. On (II) – it doesn't have to be "down." On (III), can you explain a bit more of the process? Why use a database here? Mark Guzdial

I) the red was selected because when it is circled, the program knows to only look at those specific pixels. It then iterates over those pixels (with something like for loops) and searches for RGB components. If the vlaues are within the program's definition of red, [i.e., (255, 0, 0)], then the program sets those values the new color desired. It does this by increasing or decreasing one or more of the RGB values.
II) Either you're on the wrong domain name server (something in settings might have changed) or the domain name server is having difficulties processing the English name of the site to the numerical name of the site (URL). Nothing's wrong with your internet connection.
Karin Bowman

I) i. The computer examined the pixels that were within the circle in order to determine whether or not they were red. (The computer has a predefined definition of the color red be it (255,0, 0,) etc.) The values of the pixels that were identified as red were then changed to the value of the selected color. ii. The computer knew which part was red by looking within the circle for pixels with values that equalled or were close to (255,0,0).

II. Domain name server is either broken or is rerouting the web address to the wrong URL. In this question are you asking what specifically is wrong with my computer?

III. Information for the pages on the company website aren't generated by individual people typing in HTML. Instead information is saved and stored in a standardized format by many different people. There are programs that walk over the database, gather information, and generate HTML pages. If the database is not operational, these programs cannot grab the information to make and update the pages.

Whatcha think? Melanie Nelson

Nice, Melanie. Think about the red eye algorith, though – is it really MATCHING pixels EXACTLY to red? (II) is about the domain name SERVICE not working – it could be that you're not pointing to the right domain name server, or the server itself is down. On (III), think about cnn.com and news.google.com, as well as ebay.com and amazon.com Mark Guzdial

(I)(a)The red gets replaced because the program checks every pixel and if any of those pixels fall under the program's definition of red, then the RGB value in the pixel gets reset to the color that was chosen to be the eye color.
(b)The program knows what part is red because it checks if the color of the pixels is close to red, that is, it uses a distance formula to figure that out. The distance between 2 colors is the cartesian distance between the colors as points in a 3D space, where the red, green and blue components of the color are the 3 dimensions. So if the distance is less than a certain number, (preset by the programmer as a limit beyond which the color is not a shade of red) then the color will be reset. Usually the distance is set to be less than 165.
(II)Domain name service on my computer is either down or routing the the web address to an IP address that doesnt exist.
(III)large websites rely on databases to store their information in. The html pages on a website are generated not by a person but by programs. These programs get info from the database and create/update pages at regular time intervals or when a user asks the website a query.
The company website relies on the database because:
databases are fast because they index key information.
They can be accessed using a number of different languages.
They can be "distributed"; multiple people can be uploading info and downloading info to/from the database, at the same time and from multiple computers.

Are my answers wrong? or not completely right?

Latter part of (II) is unlikely. Indexing isn't usually a key part of using a database for a website like cnn.com. Mark Guzdial

(III)a. - Dear Dad, the database is used to store large amounts of information that can be dynamically accessed via html (or other types of) code. Info, such as a large article can be accessed simply by indicating in the code where the article is in the database. Editing the page can be a case of simply changing the location of the article rather than moving the entire article itself into the html code. When the database is down, the requests for info from the dbase return null because it can't access the requested info. The website in fact exists yet the content which is supposed to be there is unavailable. Mom says be home for dinner at 5.

Thomas Sobeck

Dear Thomas, we're concerned that you're spending too much time at Georgia Tech thinking about "returning null." Can you still speak English – without referring to Wookies? Signed, Dad. :-)

IS THOMAS SOBECK'S ANSWER RIGHT?

wow...umm, probably if he's not answering. Is the algorithm used in number one chromakey?

wtf

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Sp2004 Final Exam Review last edited on 26 April 2004 at 3:49 pm by guzdial2.cc.gatech.edu