Mike wrote:
* Your second assert should be a discriminator.
Mike, you are saying that instead of this:
<xs:element name='D' type="unsignedint4">
<xs:annotation>
<xs:appinfo source=http://www.ogf.org/dfdl/>
<dfdl:assert>{(. eq 9) or (. eq 10)}</dfdl:assert>
</xs:appinfo>
</xs:annotation>
</xs:element>
I should use this:
<xs:element name='D' type="unsignedint4">
<xs:annotation>
<xs:appinfo source=http://www.ogf.org/dfdl/>
<dfdl:discriminator test="{(. eq 9) or (. eq 10)}" />
</xs:appinfo>
</xs:annotation>
</xs:element>
Would you explain the difference between those two, please?
Would you provide an example of where the former would behave incorrectly
whereas the latter would behave correctly, please?
/Roger
From: Mike Beckerle <mbecke...@apache.org>
Sent: Thursday, June 13, 2024 2:30 PM
To: users@daffodil.apache.org
Subject: [EXT] Re: Warning: Counterintuitive placement detected
Minor suggestion. Your second assert should be a discriminator. This would be a
more precise expression of exactly the criteria for choosing this sequence as
the data format. DFDL can use that to improve diagnostic behavior if both
"assertions"
ZjQcmQRYFpfptBannerStart
Minor suggestion.
Your second assert should be a discriminator.
This would be a more precise expression of exactly the criteria for choosing
this sequence as the data format.
DFDL can use that to improve diagnostic behavior if both "assertions" hold, but
something is wrong with the data for elements B, C, and D.
There is even a small possibility of an incorrect false-positive parse
happening that the discriminator rules out.
On Thu, Jun 13, 2024 at 7:52 AM Roger L Costello
<coste...@mitre.org<mailto:coste...@mitre.org>> wrote:
I found a solution that seems to work. See below. Any suggestions for improving
it is welcome.
<xs:element name="test">
<xs:complexType>
<xs:sequence>
<!--
The decimal value of the first bit of the input should be
wrapped in an <A> tag if the decimal value of the next 4 bits
equals 7 and the decimal value of the 4 bits after that equals
9,
or the decimal value of the next 4 bits equals 7 and the decimal
value of the 4 bits after that equals 10, otherwise the first
bit
of the input should be wrapped in a <B> tag.
The below is not looking ahead. Assume the input is ACD. If C
is not
equal to 7 and D is not equal to 9 or 10, then we realize that
we made an error, back up, and try the next branch of the
choice.
-->
<xs:choice>
<xs:sequence>
<xs:element name='A' type="unsignedint1"/>
<xs:element name='C' type="unsignedint4">
<xs:annotation>
<xs:appinfo source="http://www.ogf.org/dfdl/";>
<dfdl:assert>{. eq 7}</dfdl:assert>
</xs:appinfo>
</xs:annotation>
</xs:element>
<xs:element name='D' type="unsignedint4">
<xs:annotation>
<xs:appinfo source="http://www.ogf.org/dfdl/";>
<dfdl:assert>{(. eq 9) or (. eq
10)}</dfdl:assert>
</xs:appinfo>
</xs:annotation>
</xs:element>
</xs:sequence>
<xs:sequence>
<xs:element name='B' type="unsignedint1"/>
<xs:element name='C' type="unsignedint4"/>
<xs:element name='D' type="unsignedint4"/>
</xs:sequence>
</xs:choice>
</xs:sequence>
</xs:complexType>
</xs:element>
-----Original Message-----
From: Roger L Costello <coste...@mitre.org<mailto:coste...@mitre.org>>
Sent: Thursday, June 13, 2024 7:10 AM
To: users@daffodil.apache.org<mailto:users@daffodil.apache.org>
Subject: Warning: Counterintuitive placement detected
Hi Folks,
I need my DFDL to look-ahead:
The decimal value of the first bit of the input should be wrapped in an <A> tag
if the decimal value of the next 4 bits equals 7 and the decimal value of the 4
bits after that equals 9, or the decimal value of the next 4 bits equals 7 and
the decimal value of the 4 bits after that equals 10, otherwise the first bit
of the input should be wrapped in a <B> tag.
Below is my attempt at implementing this. Daffodil gives this warning message:
Schema Definition Warning: Counterintuitive placement detected. Wrap the
discriminator or assert in an empty sequence to evaluate before the contents.
(id: discouragedDiscriminatorPlacement)
Here is my DFDL:
<xs:element name="test">
<xs:complexType>
<xs:sequence>
<xs:choice>
<xs:sequence>
<xs:annotation>
<xs:appinfo source="http://www.ogf.org/dfdl/";>
<dfdl:discriminator testKind="pattern"
testPattern="(.x7x9)|(.x7xA)" />
</xs:appinfo>
</xs:annotation>
<xs:element name='A' type="unsignedint1"/>
</xs:sequence>
<xs:sequence>
<xs:element name='B' type="unsignedint1"/>
</xs:sequence>
</xs:choice>
<xs:element name='C' type="unsignedint4"/>
<xs:element name='D' type="unsignedint4"/>
</xs:sequence>
</xs:complexType>
</xs:element>
