DataNotes

DataNotes - 1 Here are additional dictionary definitions of...

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Here are additional dictionary definitions of data. Notice the third definition, it restricts data to digital data. 2
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In a broad sense, data doesn’t have to be digital. Analog data is data represented in continuous form. We are not trying to get into an argument whether matter is continuous or discrete. Quantum physics, Heisenberg’s uncertainty principle, and the dual wave/particle aspect of light—you learn about them in a different class. 3
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Here is an example of continuous data. These color photographs were taken 100 years ago by Russia’s photographer to the tsar. Are they data? Of course, they provide a lot of and important information about those times. Are they digital? No. No pixels yet. It’s even before Kodak. Notice that they are color photographs. How were they taken? Prokudin took three slides, one with a red filter in front of the lens, one with a green, and one with a blue filter. Then put the three slides on top of each other, place a bright (white) light behind them, and you project in color. RGB existed before color TVs and pixels. Why does the river look like it is covered with a film of oil? Pollution? No, of course not. Think of how the slides were taken. 4
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Here are additional examples. Music has of course been recorded with analog devices. 5
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Electronics was also analog at the beginning. 6
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What are the shortcomings of analog data? Storage is inefficient—big volume, small amount of data. Modifying the level of detail is not easy. Consider Prokudin’s photos. How could he have obtained a smaller photo from a large photo? He probably would have needed to project the large photo, then take a picture of the projection using smaller film, etc. Modifying data level of detail is essential, because not all applications need the data at the highest level of detail all the time. Transmitting analog data is also inefficient—a little bit of analog data consumes a lot of bandwidth. A few years ago, TV broadcasts switched from analog to digital. Why? In order to be able to have more channels. Replication is another huge challenge. Every time you copy analog data quality goes down. For example recording from a VCR tape to another VCR tape lower quality. That’s why you need to always use the master tape as source. This slows down replication. Instead of being able to replicate from the ever increasing number of copies, you have to always go back to the master tape. 7
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To overcome these disadvantages, the world moved to digital data. Digital data is data represented in discrete form, using numbers. For example, for digital music, I encode with a number what the music sounds like every millisecond. Since a millisecond is a very short time interval, all these values are a good approximation of the overall music. Of course, one immediate challenge is that the real world is not discrete. So in order
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This note was uploaded on 02/27/2012 for the course CS 177 taught by Professor Staff during the Spring '08 term at Purdue.

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DataNotes - 1 Here are additional dictionary definitions of...

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