[DFDL-WG] recent puzzlers on fn:count and fn:exists

[Steve Hanson]

I think we will have to go back to the XPath function spec and see what 
that says.  https://www.w3.org/TR/xpath-functions-31/#func-count.

If fn:count(.) returns the same as dfdl:occursIndex() then what is the 
point of the latter? If I recall it was added to allow a reference from 
one array to the same occurrence in another array, eg,

  dfdl:length="{/doc/lengths[dfdl:occursIndex(.)]}"

Regards
 
Steve Hanson
IBM Hybrid Integration, Hursley, UK
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
smh at uk.ibm.com
tel:+44-1962-815848
mob:+44-7717-378890
Note: I work Tuesday to Friday 



From:   Mike Beckerle <mbeckerle.dfdl at gmail.com>
To:     DFDL-WG <dfdl-wg at ogf.org>
Date:   08/10/2019 17:06
Subject:        [DFDL-WG] recent puzzlers on fn:count and fn:exists
Sent by:        "dfdl-wg" <dfdl-wg-bounces at ogf.org>




These questions came up recently from daffodil users. I know what Daffodil 
will return here, but the spec is not clear to me as to whether that's the 
right answer or is even defined.

Can an array count itself? Like this:
 
<xs:element name="name" type="xs:string" maxOccurs="unbounded">
    <xs:annotation>
        <xs:appinfo source="http://www.ogf.org/dfdl/">
            <dfdl:discriminator test="{ fn:count(.) le 5 }" />
        </xs:appinfo>
    </xs:annotation>
</xs:element>

The above can be reformulated by calling instead of fn:count, 
dfdl:occursIndex(), and that's definitely well defined in this case. But 
what does fn:count return in this case? Daffodil will return the same 
value 
as the occursIndex, because it will have speculatively attached the array 
element to the infoset at the time the fn:count function is being 
evaluated. But I don't know if that is the right answer or if we should 
simply say that fn:count is not defined in this case. 

Similarly, does an array element exist when it is being parsed?

<xs:element name="name" type="xs:string" maxOccurs="unbounded">
    <xs:annotation>
        <xs:appinfo source="http://www.ogf.org/dfdl/">
            <dfdl:discriminator test="{ fn:exists(.) }" />
        </xs:appinfo>
    </xs:annotation>
</xs:element>


Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | 
www.tresys.com
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