[DFDL-WG] clarification: fn:exactly-one function
Steve Hanson
smh at uk.ibm.com
Mon Nov 3 09:17:46 EST 2014
The main purpose envisaged for fn:exactly-one() was as a guard around
off-the-shelf XPath processors. In that scenario, throwing an error is
probably required, as what would you do otherwise?
If you wanted to return a true/false value could you just use
fn:count($arg) eq 1 instead of fn:exactly-one() ?
Regards
Steve Hanson
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848
From: Mike Beckerle <mbeckerle.dfdl at gmail.com>
To: "dfdl-wg at ogf.org" <dfdl-wg at ogf.org>
Date: 30/10/2014 10:00
Subject: [DFDL-WG] clarification: fn:exactly-one function
Sent by: dfdl-wg-bounces at ogf.org
According to the DFDL spec, fn:exactly-one returns "True if the provided
sequence contains exactly one node/value," which suggests that the
function would return false if the sequence contains > or < 1 node/value.
The XPath description states that fn:exactly-one "returns $arg if it
contains exactly one item. Otherwise, raises an error."
It seems of value to have a true/false result, because something that
raises an error like this can only be used as an assertion effectively. On
the other hand, that's not what XPath does.
Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology |
www.tresys.com
Please note: Contributions to the DFDL Workgroup's email discussions are
subject to the OGF Intellectual Property Policy
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