Editing 2739: Data Quality
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==Explanation== | ==Explanation== | ||
+ | {{incomplete|Created by a SUPERIOR FELINE. Do NOT delete this tag too soon.}} | ||
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! Explanation | ! Explanation | ||
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| {{w|Bloom filter}} | | {{w|Bloom filter}} | ||
− | + | | A Bloom filter is a probabilistic data structure that can efficiently say whether an element is ''probably'' part of the dataset, while it can say "element is not in set" with 100% accuracy. If a Bloom filter is used to compress the contents of a book, the Bloom filter can re-tell a similar story - just by guessing.{{fact}} | |
− | | A Bloom filter is a probabilistic data structure that can efficiently say whether an element is ''probably'' part of the dataset, while it can say "element is not in set" with 100% accuracy. If a Bloom filter is used to | ||
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| {{w|Hash table}} | | {{w|Hash table}} | ||
− | + | | A hash table allows you to find data very fast. Randall probably means hashing the contents of entire books. Calculating a hash value for an entire book means that there is (most probably) a unique relationship between the book and a hash value - e.g. "58b8893b2a116d4966f31236eb2c77c4172d00e9". This means the book will yield this exact hash value, though it's impossible to reconstruct the book's content from a hash value. It is a highly efficient, but is meaningless: An average book contains several millions of bits, yet the SHA-2 hash has only 256 bits. | |
− | | A hash table allows you to find data very fast. Randall probably means hashing the contents of entire books. Calculating a hash value for an entire book means that there is (most probably) a unique relationship between the book and a hash value - e.g. " | ||
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| {{w|JPEG|JPG}}, {{w|GIF}}, {{w|MPEG-1|MPEG}} | | {{w|JPEG|JPG}}, {{w|GIF}}, {{w|MPEG-1|MPEG}} | ||
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| Image and video formats that are considered 'lossy'. JPG (or "JPEG") format and the MPEG {{w|MPEG-2|group}} {{w|Advanced Video Coding|of}} formats typically use a range of data-compression methods that save space by selectively fudging (thus losing) what details it can of the image (and audio, where appropriate), to make disproportionate gains in compression; best used for real world images (and films) where real-world 'noise' can afford to be replaced by a more compressible version, without too much obvious change. | | Image and video formats that are considered 'lossy'. JPG (or "JPEG") format and the MPEG {{w|MPEG-2|group}} {{w|Advanced Video Coding|of}} formats typically use a range of data-compression methods that save space by selectively fudging (thus losing) what details it can of the image (and audio, where appropriate), to make disproportionate gains in compression; best used for real world images (and films) where real-world 'noise' can afford to be replaced by a more compressible version, without too much obvious change. | ||
− | GIF compression is not 'lossy' in the same way, i.e. whatever it is asked to encode can be faithfully decoded, but Randall may consider its limitations (it can only write images of 256 unique hues, albeit that these can come from anywhere across the whole 65,536 "True color" range, plus transparency) to be a form of loss, as conversion from a more sophisticated format (e.g. PNG, below) could lose many of the subtle shades of the original and produce an inferior image. For this reason, GIF format | + | GIF compression is not 'lossy' in the same way, i.e. whatever it is asked to encode can be faithfully decoded, but Randall may consider its limitations (it can only write images of 256 unique hues, albeit that these can come from anywhere across the whole 65,536 "True color" range, plus transparency) to be a form of loss, as conversion from a more sophisticated format (e.g. PNG, below) could lose many of the subtle shades of the original and produce an inferior image. For this reason, GIF format became one best left to render diagrams and other computer-generated imagery with swathes of identical pixels and mostly sharp edges (and to utilize the optional transparent mask). Alternatively, he may just have included it as a joke/nerd-snipe. |
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− | | {{w|PNG}}, {{w|ZIP (file format)|ZIP}}, {{w|TIFF}}, {{w|WAV}} | + | | {{w|PNG}}, {{w|ZIP (file format)|ZIP}}, {{w|TIFF}}, {{w|WAV}} |
− | + | | A series of formats using lossless compression. PNG and TIFF are image formats, that are suitable for photos but without resorting to reduced accuracy in order to assist compression. WAV is an audio format that also does not arbitrarily sacrifice 'unnecessary' details, unlike the more recently developed {{w|MP3|MPEG Audio Layer III}} which has become the de-facto consumer audio format for many. | |
− | | A series of formats using lossless compression. PNG and TIFF are image formats that are suitable for photos | + | ZIP is a generic compression algorithm(/format) that can be used to store any other digital file, for exact decompression later on, although any file(s) already compressed in some way are not likely to compress significantly more. |
− | ZIP is a generic compression algorithm ( | ||
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− | | | + | | Parity bits for error detection |
− | | | + | | In the number 135, the sum of digits is 9. So, the number 135 could be written as "135-9". If the number was tampered with, the parity bits could tell you so (in some cases), or possibly that the parity itself was the digit that was miswritten. But a change from "135" to "153" could not be detected that way. There are more reliable means to detect errors: The obsolete CRC-32 and MD5, and the much more modern {{w|Secure Hash Algorithm|SHA}}. |
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− | | | + | | Parity bits for error correction |
− | | | + | | There are ways to restore the original data with the given additional data. One method is to 'overload' with multiple different methods of error-detection parity such that any small enough corruption of data (including of the parity bits themselves) can be reconstructed to the correct original value. One of the first such methods is {{w|Hamming(7,4)}}, invented around 1950. A practical application of error correction would be {{w|QR_code#Error_correction|QR Codes}} using {{w|Reed–Solomon error correction|Reed–Solomon error correction}}. |
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==Transcript== | ==Transcript== | ||
− | :[A line chart is shown with eight unevenly-spaced ticks each one with a label beneath the line. Above the middle of the line there is a dotted vertical line with a word on either side of this divider. Above the chart there is a big caption with an arrow beneath it | + | :[A line chart is shown with eight unevenly-spaced ticks each one with a label beneath the line. Above the middle of the line there is a dotted vertical line with a word on either side of this divider. Above the chart there is a big caption with an arrow pointing right beneath it.] |
:<big>Data Quality</big> | :<big>Data Quality</big> | ||
:Lossy ┊ Lossless | :Lossy ┊ Lossless |