# User talk:Toni 001

## formatter URI for RDF resource (P1921)Edit

Hello Toni and welcome to Wikidata! I allowed myself to revert your edits on the formatter URI for RDF resource (P1921) for MusicBrainz ids because MuscBrainz doc specifies that the URIs for their objects use the http:// protocol. formatter URI for RDF resource (P1921) is used for RDF identifiers and are not used as links to a web page escribing the identified entity, there is formatter URL (P1630) for this use case. Tpt (talk) 14:57, 30 January 2019 (UTC)

- Thanks, you are right, I had missed this documentation. I was following their embedded JSON-LD (example, look at the source and search for
`application/ld+json`

) which uses the`https`

scheme. I filed a ticket with MusicBrainz. Let's see whether they can make JSON-LD and their documentation consistent. Toni 001 (talk) 15:28, 30 January 2019 (UTC)

## Community Insights SurveyEdit

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RMaung (WMF) 16:25, 9 September 2019 (UTC)

## Reminder: Community Insights SurveyEdit

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## Coherent?Edit

Hello, Tony! What do you mean by temperature difference (Q69362767)? What's the difference from temperature (Q11466)? I suppose both can be measured in Kelvins (or Celsium degrees). --Infovarius (talk) 17:24, 1 October 2019 (UTC)

- @Infovarius: Hi. I would like to classify units into coherent SI unit (Q69197847), as defined in SI Brochure (9th edition) (Q68977219). To do this right it makes a difference whether a unit measures a temperature or a temperature difference. See for instance page 141 of the English SI brochure where it reads "Special care must be taken when expressing temperatures or temperature differences, respectively.". Further, the last sentence of the paragraph, reads "The unit degree Celsius is only coherent when expressing temperature differences.". This means that "degree Celsius" (measuring absolute temperature) is not a coherent SI unit, while "degree Celsius difference" (measuring, well, a difference) is. Toni 001 (talk) 17:43, 1 October 2019 (UTC)
- Hm, strange. Because "degree Celsius" has no prefixes in both uses (if there are 2 uses at all). Or do I understand coherent SI unit (Q69197847) wrong? --Infovarius (talk) 20:18, 3 October 2019 (UTC)
- Maybe my initial response was too cryptic, but I realized that only after posting it. The simple answer (to your initial question): Different physical quantities can be measured in the same unit, there is no problem with that. Take for instance "length", "diameter", "radius", "wavelength", ..., all of which are "lengths" and can therefore be measured in "metre" (or kilometre, micrometre, ...). Now to "coherent": The "Celsius scale" (which, by the way, is a scale, not a unit - see my comment on your talk page) defines a unit, the "degree Celsius". When measuring temperature differences, say "yesterday it was 30°C and today it was 25°C" then the "temperature difference" is 5°C (note how both "temperature" and "temperature difference" use the same unit symbol). The distinction between differences and absolute values does not exist for other SI units, say length. How can you see that? Start with a stick of 10 cm. Now ask: What's twice as long? Easy, two sticks, measuring 20 cm. You can also convert 10 cm to 1 dm, then multiply by two, arriving at 2 dm, and after that, convert it back to 20 cm. The result is the same. Now try the same exercise with absolute temperatures (using °C): Start with an absolute temperature of, say, 5°C. What is twice as hot?
*Now the error starts*: Easy, 10 °C. Now, try to do the round-trip over Kelvin. 5°C are (about) 283 K; multiply by 2, you get 566 K; now convert back to the Celsius scale: 293 °C. Oh, that's not consistent. The explanation for this error is that the "absolute degree Celsius" is not coherent. But feel free to do an exercise with "degree Celsius difference" - that means, imagine an appropriate situation where you measure temperature differences (heat capacity, ...) - and you'll see that it works out, just as it should for "coherent SI units". Toni 001 (talk) 20:50, 3 October 2019 (UTC)

- Maybe my initial response was too cryptic, but I realized that only after posting it. The simple answer (to your initial question): Different physical quantities can be measured in the same unit, there is no problem with that. Take for instance "length", "diameter", "radius", "wavelength", ..., all of which are "lengths" and can therefore be measured in "metre" (or kilometre, micrometre, ...). Now to "coherent": The "Celsius scale" (which, by the way, is a scale, not a unit - see my comment on your talk page) defines a unit, the "degree Celsius". When measuring temperature differences, say "yesterday it was 30°C and today it was 25°C" then the "temperature difference" is 5°C (note how both "temperature" and "temperature difference" use the same unit symbol). The distinction between differences and absolute values does not exist for other SI units, say length. How can you see that? Start with a stick of 10 cm. Now ask: What's twice as long? Easy, two sticks, measuring 20 cm. You can also convert 10 cm to 1 dm, then multiply by two, arriving at 2 dm, and after that, convert it back to 20 cm. The result is the same. Now try the same exercise with absolute temperatures (using °C): Start with an absolute temperature of, say, 5°C. What is twice as hot?

- Hm, strange. Because "degree Celsius" has no prefixes in both uses (if there are 2 uses at all). Or do I understand coherent SI unit (Q69197847) wrong? --Infovarius (talk) 20:18, 3 October 2019 (UTC)

- @Infovarius: Hi. I would like to classify units into coherent SI unit (Q69197847), as defined in SI Brochure (9th edition) (Q68977219). To do this right it makes a difference whether a unit measures a temperature or a temperature difference. See for instance page 141 of the English SI brochure where it reads "Special care must be taken when expressing temperatures or temperature differences, respectively.". Further, the last sentence of the paragraph, reads "The unit degree Celsius is only coherent when expressing temperature differences.". This means that "degree Celsius" (measuring absolute temperature) is not a coherent SI unit, while "degree Celsius difference" (measuring, well, a difference) is. Toni 001 (talk) 17:43, 1 October 2019 (UTC)

## New page for cataloguesEdit

Hi, I created a new page for collecting sites that could be added to Mix'n'match and I plan to expand it with the ones that already have scrapers by category. Feel free to expand, use for property creation. Best, --Adam Harangozó (talk) 12:00, 21 October 2019 (UTC)