Property talk:P820

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arXiv classification
arXiv classification of pre-print articles

Description	arXiv classification, e.g. hep-th. Optional. To be used as qualifier of the property arXiv ID (P818).
Applicable "stated in" value	arXiv (Q118398)
Data type	String
Domain	sources (note: this should be moved to the property statements)
Allowed values	According to this template: see: Understanding the arXiv identifier According to statements in the property: (astro-ph|cond-mat|gr-cq|hep-ex|hep-lat|hep-ph|hep-th|math-ph|nlin|nucl-ex|nucl-th|physics|quant-ph|math|cs|CoRR|q-bio|q-fin|stat)\.[A-Z]{2} When possible, data should only be stored as statements
Example	According to this template: <A catalogue of multiplicity among bright stellar systems (Q14558831)> arXiv eprint identifier <0806.2878>; qualifier arXiv classification <astro-ph>. According to statements in the property: A simple proof of the Gaussian correlation conjecture extended to some multivariate gamma distributions (Q29167299) → math.PR Spatially-resolved, substrate-induced rectification in C₆₀ bilayers on copper (Q111286372) → cond-mat.mes-hall Spectrum of structure for jammed and unjammed soft disks (Q105824453) → cond-mat.soft When possible, data should only be stored as statements
Source	Template:Cite arXiv (Q6927043) (note: this information should be moved to a property statement; use property source website for the property (P1896))
Formatter URL	https://arxiv.org/list/$1/recent
See also	arXiv author ID (P4594), arXiv ID (P818)
Lists	Items with the most statements of this property Count of items by number of statements (chart) Items with the most statements Items with the fewest statements Count of items by number of sitelinks (chart) Items with the most sitelinks Items with the most sitelinks, but no link to one Wikipedia (sample: Welsh Wikipedia, cywiki) Items with the fewest sitelinks Most linked wikis Items with the most identifier properties Items with no other statements Most recently created items Items with novalue claims Items with unknown value claims Usage history (total) Usage history (main statement) Chart by item creation date Database reports/Constraint violations/P820 Map Random list
Proposal discussion	Proposal discussion
Current uses	Total 3,387 Main statement 2,246 66.3% of uses Qualifier 1,139 33.6% of uses Reference 2 <0.1% of uses
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[create Create a translatable help page (preferably in English) for this property to be included here]

Scope is as qualifier (Q54828449): the property must be used by specified way only (Help)

Exceptions are possible as rare values may exist. Exceptions can be specified using exception to constraint (P2303).
List of violations of this constraint: Database reports/Constraint violations/P820#Scope, SPARQL

Allowed entity types are Wikibase item (Q29934200): the property may only be used on a certain entity type (Help)

Exceptions are possible as rare values may exist. Exceptions can be specified using exception to constraint (P2303).
List of violations of this constraint: Database reports/Constraint violations/P820#Entity types

Qualifier

After the approval of this property, I suggested to the proposer to transform this property as qualifier for arXiv ID (P818). Here and here the discussion. --Paperoastro (talk) 21:04, 28 August 2013 (UTC)

Why should this not be used as a main property? It makes more sense to me that it is a main property as arXiv classification (P820) does not in any way change or restrict the semantics of arXiv ID (P818)? You can easily use arXiv classification (P820) independently of arXiv ID (P818). — Finn Årup Nielsen (fnielsen) (talk) 13:37, 30 March 2018 (UTC)

@Daniel Mietchen, Paperoastro: "I think it is a good idea since both come together." from [1] is one argument. However, both values are independent of each others (you can have one without the knowledge of the other), so making one a qualifier of the other makes it unnecessarily complicated, I think. In Scholia (Q45340488), I have programmed a ArXiv scraper to output the arXiv classification as a main property. We now have a pull request to change that so it becomes a qualifier. I do not understand "where I use P820 both as qualifier and "main property" from [2]: As far as I can tell it was always used as a qualifier and not both. — Finn Årup Nielsen (fnielsen) (talk) 16:32, 1 February 2023 (UTC)

I feel like this should be a qualifier, since it applies specifically to an arXiv identifier. Articles, as far as I can tell, are not limited to a single identifier, so this should be a qualifier to avoid ambiguity. --Tomodachi94 (talk) 05:37, 2 February 2023 (UTC)

@Tomodachi94, Fnielsen, Paperoastro: I think every paper with an arXiv classification has an arXiv identifier, and while the inverse is probably true as well (not entirely sure here), the identifier helps find and disambiguate the papers, and treating the classification as a qualifier to the identifier helps avoid cases where we have arXiv classification (P820) statements without corresponding arXiv ID (P818) statements. --Daniel Mietchen (talk) 01:13, 3 February 2023 (UTC)

@Tomodachi94, Daniel Mietchen, Paperoastro: "Articles, as far as I can tell, are not limited to a single identifier": I have never seen that. "the identifier helps find and disambiguate the papers": I do not understand. As far as I know the arXiv ID (P818) is unique and does not require a arXiv classification to be unique. Or am I missing some understanding here? — Finn Årup Nielsen (fnielsen) (talk) 12:31, 3 February 2023 (UTC)

@Tomodachi94, Fnielsen, Paperoastro: Yes, "arXiv ID (P818) is unique and does not require a arXiv classification". However, every entity on arXiv.org that has an arXiv classification should have a arXiv ID (P818) statement, so attaching the arXiv classification (P820) statements to it seems like a good idea. --Daniel Mietchen (talk) 21:42, 6 February 2023 (UTC)

Why the single value restriction?

Why the single value restriction? For instance, https://arxiv.org/abs/1605.02688 has "Subjects: Symbolic Computation (cs.SC); Learning (cs.LG); Mathematical Software (cs.MS)". There are 3 subjects there (albeit one main subject - bolded). — Finn Årup Nielsen (fnielsen) (talk) 16:33, 3 April 2018 (UTC)

I just encountered this as well. I've removed the constraint. Papers on arxiv are frequently listed with multiple arxiv categories, so this constraint really doesn't make sense. Thanks. Mike Peel (talk) 09:38, 21 July 2022 (UTC)

quant-ph

Is the format constraint correct in rejecting the value "quant-ph"? It looks like it's valid, without the \.[A-Z]{2} suffix. It's used on Quantum Darwinism, classical reality, and the randomness of quantum jumps (Q58246729), for example. Ghouston (talk) 00:26, 6 November 2018 (UTC)

Perhaps a format change is in order

I don't know how to change formats, but I think a format change is necessary. I think cond-mat.soft should, for example, comply with the format, but it doesn't. See https://arxiv.org/list/cond-mat.soft/recent but is not a link given entry here, Spectrum of structure for jammed and unjammed soft disks (Q105824453) (or have I used it incorrectly?). Thanks, Trilotat (talk) 15:25, 8 March 2021 (UTC)

We could just delete the constraint, if it doesn't work in all cases. Ghouston (talk) 21:57, 8 March 2021 (UTC)

I deprecated it so that it shouldn't raise an error now, I think. Arlo Barnes (talk) 06:20, 19 March 2022 (UTC)