For generic xml without a dtd or schema, there is no wrong XPath as who is to
say that element might exist somewhere or sometime. It would be nice if there
was a way to validate an XPath against a given did or schema to indicate a path
would never exist.Sent from my Verizon, Samsung Galaxy smartphone
-------- Original message --------From: "Roger L Costello
costello(_at_)mitre(_dot_)org"
<xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> Date: 10/14/21 6:45
AM (GMT-08:00) To: xsl-list(_at_)lists(_dot_)mulberrytech(_dot_)com Subject:
[xsl] My XPath mistakenly referenced an element that doesn't exist
and I got no error message ... is this bad language design? Hi
Folks,Here is my (very simple) XML document: <Document>Hello,
world</Document>My XSLT program contains a xsl:value-of with a simple XPath
expression: <xsl:template match="/"> <xsl:value-of
select="Document/foo eq 'abc'"/> </xsl:template>In the XPath expression I
mistakenly referenced an element -- foo -- that does not exist.I ran the XSLT
program on the XML document. No error was generated.My colleague argues that
such behavior is bad language
design:---------------------------------------------------Languages which
define such mistakes to just return "empty" node lists or false, or such are
not helping anybody. They just turn author mistakes into silent, hard-to-detect
behaviors. In my view this is a major mistake in the XPath language. All path
expressions should be strongly, statically type-correct, so Document/foo has to
be a possible path. But if element foo is optional, then any given instance may
not have element foo and so a path like Document/foo can be type correct, but
meaningless for a particular data document. One can explicitly test, e.g., if (
exists(Document/foo) ) then (Document/foo eq 'abc') else.... If you just use
the expression without this test, and node foo doesn't exist, then it should
cause a failure. ---------------------------------------------------Do you
agree with my colleague's assessment? Is this behavior in XPath an indication
of bad language design?/Roger
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