explain xkcd - User contributions [en]

2739: Data Quality

2023-02-20T20:17:55Z

Rupumped: /* Explanation */ Possible Norbert Wiener reference

{{comic
| number = 2739
| date = February 17, 2023
| title = Data Quality
| image = data_quality_2x.png
| imagesize = 671x211px
| noexpand = true
| titletext = [exclamation about how cute your cat is] -> [last 4 digits of your cat's chip ID] -> [your cat's full chip ID] -> [a drawing of your cat] -> [photo of your cat] -> [clone of your cat] -> [your actual cat] -> [my better cat]
}}

==Explanation==
{{incomplete|Created by a SUPERIOR FELINE. Do NOT delete this tag too soon.}}


Digital data are transferred in bits, and {{w|data loss}} is the process by which some of these bits are lost or altered during data transport. Data can also be compressed to make transmission and/or storage more efficient; some {{w|compression algorithms}} discard some data to improve the compression (this can be acceptable in audio or visual data, since the difference may be hard for humans to perceive).

This comic shows a chart in the form of a line, moving in increasing quality from most lossy to most lossless. However, the highest quality, "better data", is using a different sense of the term "quality". In the context of data transmission or compression, it refers to how accurately the result represents the original. But in this case, he's referring to its more general excellence.

The title text uses your cat as an example of this range of losses (or, in the case of the latter reaches of the graph, gains) in the data. This is possibly a reference to [https://www.goodreads.com/quotes/8157292-the-best-material-model-of-a-cat-is-another-or Norbert Wiener]'s quote, "The best material model of a cat is another, or preferably the same, cat." The most lossy is an exclamation about how cute your cat is, which is ephemeral and obviously carries very little significance in terms of actually providing specific, transferrable information about your cat. The example then progresses into your cat's chip ID; presumably your cat has been microchipped, and between the last four digits (commonly used in sensitive information as an identifier without revealing the full number) or the entire chip ID, provides a still-uninformative yet slightly improved way of identifying your cat. A drawing of your cat and a photo of your cat would portray the cat reasonably well, while a clone of your cat and (of course) your actual cat would be the best way of gaining data about your cat. However, as in the actual comic, the final, most lossless (in this case, with the most gain) form of data transfer has nothing to do with your cat, but is simply Randall's better cat. This is apparently made out by Randall to be the pinnacle of cat data.

=== Details ===
{| class="wikitable"
|-
! Item
! Explanation
|-
| {{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.
|-
| {{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 vaue. 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.
|-
| {{w|JPEG|JPG}}, {{w|GIF}}, {{w|MPEG-1|MPEG}}
| 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 vesion, 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 became one best left to render diagrams and other computer-generated imagery with swathes of identical pixels and mostly sharp edges (and to utilise the optional transparent mask). Alternatively, he may just have included it as a joke/nerd-snipe.
|-
| {{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 defacto consumer audio format for many.
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.
|-
| 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}}.
|-
| 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.
|}

==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 pointing right beneath it.]
:<big>Data Quality</big>
:Lossy ┊ Lossless

:[Labels to the left of the dotted line from left to right:]
:Someone who once saw the data describing it at a party
:Bloom filter
:Hash table
:JPEG, GIF MPEG

:[Labels to the right of the dotted line from left to right:]
:PNG, ZIP, TIFF, WAV, Raw data
:Raw data + parity bits for error detection
:Raw data + parity bits for error ''correction''
:Better data

{{comic discussion}}

[[Category:Charts]]
[[Category:Cats]]

1661: Podium

2016-03-28T23:37:58Z

Rupumped: /* Corrected ending of sentence with preposition */

{{comic
| number = 1661
| date = March 28, 2016
| title = Podium
| image = podium.png
| titletext = BREAKING: Senator's bold pro-podium stand leads to primary challenge from prescriptivist base.
}}

==Explanation==
{{incomplete|More on the info in the title text and links to dictionaries should be real links.}}
The comic is playing on a stereotypical politician, without any real beliefs, here represented by [[Cueball]] without any features, but they want to appear to stand for something. Alternatively, this is what might happen if someone like Cueball (or the strip's author Randall), who tend to think literally and who get interested in and distracted by tangents, were running.

Thus, Cueball picks up what is, in some circles, an argument: whether the standing desk used by public speakers should be called a "{{w|podium}}" or a "{{w|lectern}}." This argument is actually common among members of {{w|Toastmasters International}}, though it would usually not rise to the level of needing to be part of a national discourse.

Technically — or at least, in original use or etymologically — a podium is the stage or raised platform, on which Cueball is standing. Those on the "anti-podium" side state - correctly - that "podium" derives from the Greek word "pous/podos" meaning "foot" and thus denotes "a small platform for the conductor of an orchestra, for a public speaker, etc." (dictionary.com). This is the prescriptivist position - mentioned in the title text - indicating that dictionaries and similar publications prescribe how words should be used. However common in teaching institutions with their power hierarchies, the very notion of dictionaries as prescriptive is wrong relative to traditional standards of lexicographers, e.g. to require use of a word in 12 fields of usage over 20 years before formal adoption, with certain exceptions. In effect when dictionaries are backwards looking specialized sociology history documents, such "teaching" of prescriptivist positions becomes a mix of fraud and cultural insanity to demand false authority, noting the nature of politicians themselves to often act as false authorities.

The literal distinction between podium and lectern (or the meaning of "this thing") is not obvious from context, when the meaning of ''podium'' has drifted in common use to refer to the small standing desk the speaker stands behind, puts papers on, etc. — i.e. the lectern. This is the descriptivist view that so many people "misuse" the word that "podium" now can validly refer to the small standing desk behind which speakers often stand. Dictionary.com lists "lectern" as definition #3 for "podium."

Sometimes, [http://www.platformgiant.com/podium-vs-lectern people care about this]. The fact is, though the etymological definition is clear (the lectern is the desk that stands on the podium), and the difference might be important if you were setting up an auditorium, in common usage it really doesn't matter. If a public speaker is asked to step up to the podium, very few would quibble over the usage.

The idiomatic idea of "stepping up" to the podium could remain accurate even if one then uses a lectern, when the lectern is the reading desk placed on the elevated podium. That idiom shifts to entirely metaphorical when a lectern in many classrooms or meeting rooms is at floor level. With a shift towards virtual meeting spaces, and meeting rooms with computer driven audio-visual systems, the idea of both podiums as physical platforms, and lecterns as desks for reading matter when they're increasingly AV control centers, are changing. Such change further upends the idea of dictionaries as prescriptivist, given the nature of language to develop new words or alter meanings of necessity, versus sloppy common usage.

The title text implies that Cueball moves ahead with his promised research and ends up coming out on the side of calling it a podium. This leads to the people who follow the prescriptivist position to organize and put forward a political candidate to challenge Cueball in the {{w|primaries}}. In the U.S., the primaries are used to select a single candidate from a particular party to represent that party at final election (whether national or on a state level).

==Transcript==
:[Cueball is speaking at a lectern standing on a podium.]
:Cueball: The American people are tired of politics as usual.
:Cueball: They're tired of-
:Cueball: Okay, brief tangent: is this thing a podium or a lectern? People say "podium" is wrong, but I also see it used that way in pretty formal contexts. Is usage just changing?
:Cueball: If elected, I will get to the bottom of this for once and for all.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Politics]]
[[Category:Language]]