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Fix invalid syntax #70

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merged 3 commits into from
Feb 8, 2023
Merged

Fix invalid syntax #70

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bac0fb2
Fix typos / Remove pica-rs
nwagner84 Feb 4, 2023
c7f9fe1
Revert "Fix typos / Remove pica-rs"
nwagner84 Feb 8, 2023
ba8a71b
Fix invalid "EBNF"
nwagner84 Feb 8, 2023
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28 changes: 14 additions & 14 deletions pages/query/picapath.md
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Expand Up @@ -7,7 +7,7 @@ created: 2014
creator: Jakob Voß
---

Mit **PICA Path** Ausdrücken lassen sich einzelne Felder, Unterfelder und Feldinhalte von [PICA](../pica)-Daten referenzieren. Das Format ist von [MARCSpec](marcspec) inspiriert und wird im Rahmen der Werkzeuge [picadata](https://metacpan.org/dist/PICA-Data/view/script/picadata), Catmandu und [pica-rs](https://github.com/deutsche-nationalbibliothek/pica-rs) entwickelt.
Mit **PICA Path** Ausdrücken lassen sich einzelne Felder, Unterfelder und Feldinhalte von [PICA](../pica)-Daten referenzieren. Das Format ist von [MARCSpec](marcspec) inspiriert und wird im Rahmen der Werkzeuge [picadata](https://metacpan.org/dist/PICA-Data/view/script/picadata) und Catmandu entwickelt.
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@nichtich nichtich Feb 7, 2023 •
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PICA Path is being standardized to unify (at least list a tiny subset of) syntax of several applications (I counted five at least) that all happend to invent their own way to solve a seemingly simple task: reference PICA fields and subfields. PICA Path and pica-rs have already been aligned to prevent xkcd 927 and yet another syntax in the future. Missing steps of the compromise are explained at deutsche-nationalbibliothek/pica-rs#579 (comment).


<example title="Beispiele">
003@
Expand All @@ -21,24 +21,24 @@ Mit **PICA Path** Ausdrücken lassen sich einzelne Felder, Unterfelder und Feldi
Zur vollständigen Unterstützung von PICA Path muss mindestens folgende formale Syntax erkannt werden:

~~~
path ::= ( tag | xtag ) occurrence? subfields?
tag ::= [012.] [0-9.] [0-9.] [A-Z@.]
xtag ::= "2" [0-9.] [0-9.] [A-Z@.] "x" number
occurrence ::= "/" occurenceValue
occurenceValue ::= number "-" number | occurrencePattern | "*"
occurencePattern ::= [0-9] [0-9]? [0-9]?
subfields ::= [$.]? ( [A-Za-z0-9]+ | "*" )
number ::= [0-9]+
path ::= ( tag | xtag ) occurrence? subfields?
tag ::= [012.] [0-9.] [0-9.] [A-Z@.]
xtag ::= "2" [0-9.] [0-9.] [A-Z@.] "x" number
occurrence ::= "/" occurrenceValue
occurrenceValue ::= number "-" number | occurrencePattern | "*"
occurrencePattern ::= [0-9] [0-9]? [0-9]?
subfields ::= [$.]? ( [A-Za-z0-9]+ | "*" )
number ::= [0-9]+
~~~

Als Standard-Erweiterungen sind die Angabe von Positionen in Unterfeldwerten (`position`) und eine alternative Syntax zur Angabe von Occurrences möglich (umgesetzt in den Werkzeugen `picadata` und `Catmandu`):

~~~
path ::= ( tag | xtag ) occurrence? ( subfields position? )?
position ::= "/" ( number | range )
range ::= number "-" number? | "-" number
occurrence ::= "/" occurenceValue | "[" occurrenceValue "]"
occurencePattern ::= [0-9.] [0-9.]? [0-9.]?
path ::= ( tag | xtag ) occurrence? ( subfields position? )?
position ::= "/" ( number | range )
range ::= number "-" number? | "-" number
occurrence ::= "/" occurrenceValue | "[" occurrenceValue "]"
occureencePattern ::= [0-9.] [0-9.]? [0-9.]?
~~~

Positionsangaben beziehen sich nicht auf Bytes sondern auf Unicode-Codepunkte. Bei Positionsangaben über mehrere Unterfelder werden die Unterfeldwerte in Reihenfolge ihres Vorkommens im Feld zu einer Zeichenkette zusammengefügt.
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