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Previous Stack questions indicate that in certain implementations of XQuery, returning attributes directly from a path expression (e.g. `$doc//@name') fails to display results and yields runtime errors:

Can't select XML attributes with Oxygen XQuery implementation; Oxygen XPath emits result

XQuery unable to select attribute

While attribute values can be returned using the string() or data() functions, I'm still confused as to why this limitation exists at all. The former link suggests that it is indeed the OXygen IDE itself, independent of the XQuery processor. However, when I try to return attributes directly I get the following runtime error message: 

error: Failed to invoke method retrieveFirstChunk in class  org.exist.xmlrpc.RpcConnection: org.xml.sax.SAXException: 
Error SENR0001: attribute 'notBefore' has no parent element

Since this error message is from the processor, could the type of processor play a role? I'm using eXist-db as my data source and processor.

Ethan Powell
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1 Answers1

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I don't know the specifics of the particular products involved, but the basic situation is that XQuery can return an attribute or sequence of attributes, but the standard XQuery 1.0 serialization methods can't display the value. For example a query like //@id will select a sequence of attributes all named "id" and there is no way of serializing this as XML. The "adaptive" serialization method was introduced in XQuery 3.1 largely as a response to this problem: it's designed to display the results in human-readable form, not to output well-formed XML.

Michael Kay
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  • Mike is correct. The issue is with XQuery serialization. Adaptive serialization was just released in eXist 3.3.0 yesterday, so I doubt oXygen support that yet. In the mean time to you need to extract the string value of your attributes using `string(@attr)` to comply with the W3C XQuery serialization specs. – adamretter Jul 03 '17 at 16:13