Thank you David. -Allan.
On Mon, Jun 20, 2016 at 11:19 PM, David G. Johnston < david.g.johns...@gmail.com> wrote: > On Sun, Jun 19, 2016 at 5:09 PM, Allan Kamau <kamaual...@gmail.com> wrote: > >> I have an xml document from which I would like to extract the contents of >> several elements. >> >> I would like to use xpath to extract the contents of "name" from the xml >> document shown below. >> >> WITH x AS >> ( >> SELECT >> '<?xml version="1.0" encoding="UTF-8"?> >> <uniprot xmlns="http://uniprot.org/uniprot"; xmlns:xsi=" >> http://www.w3.org/2001/XMLSchema-instance"; xsi:schemaLocation=" >> http://uniprot.org/uniprot >> http://www.uniprot.org/support/docs/uniprot.xsd";> >> <entry dataset="Swiss-Prot" created="2009-12-15" modified="2016-05-11" >> version="56"> >> <accession>A0JM59</accession> >> <name>UBP20_XENTR</name> >> </entry> >> </uniprot> >> '::xml AS d >> ) >> SELECT (xpath('/uniprot/entry/name/text()',a.d))[1]::text AS uniprot_name >> FROM >> x AS a >> ; >> >> The documentation for xpath() (" >> https://www.postgresql.org/docs/9.5/static/functions-xml.html";) >> describes "xpath(xpath, xml [, nsarray]"). >> >> For the above xml document, what would be the two dimensional array >> "nsarray" for the xpath() function? >> > > Is there a specific part of the description and two examples that doesn't > make sense to you? > > Or more specifically, do you understand what namespaces are? > > ARRAY[ > ARRAY['defaultns','http://uniprot.org/uniprot'], > ARRAY['xsi','http://www.w3.org/2001/XMLSchema-instance'] > ] > > In effect when the xpath function parses the XML document it tosses away > all of the document-local namespace aliases and instead associated the full > namespace URI with each element (in the DOM). Since, in the xpath > expression, usually you'd want to refer to nodes in the DOM via their > namespace alias you need to tell the xpath function which aliases you > intend to use in the xpath and which full URI they correspond to. > Furthermore, there is not concept of a default namespace in the xpath > expression. So while you can simply copy-paste the aliases and URIs from > all of the non-default namespace aliases you must also choose a unique > alias for the default namespace in the original document. > > In the above I've copied the alias and namespace URI for the named "xsi" > alias and gave the name "defaultns" to the original document's default > namespace URI. > > David J. > >
