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https://issues.apache.org/jira/browse/DAFFODIL-2277?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Mike Beckerle updated DAFFODIL-2277:
------------------------------------
Description:
Daffodil should issue a warning, possibly even an SDE, about misplaced
discriminators:
I observed that many things with discriminators are coded like this:
```
<xs:sequence>
<xs:annotation><xs:appinfo source="http://www.ogf.org/dfdl/";>
<dfdl:discriminator ....../>
</xs:appinfo></xs:annotation>
....rest of sequence...
</xs:sequence>
```
So, it's quite unintuitive, but that discriminator will be executed AFTER the
rest of the sequence.
I'm not sure why we decided that is how DFDL should work, but to get the
discriminator to run BEFORE the rest of the sequence, which is typically what
you want from a discriminator, you must nest it within ANOTHER sequence inside
the first like so:
```
<xs:sequence>
<xs:sequence>
<xs:annotation><xs:appinfo source="http://www.ogf.org/dfdl/";>
<dfdl:discriminator ....../>
</xs:appinfo></xs:annotation>
</xs:sequence>
....rest of sequence...
</xs:sequence>
```
Daffodil should issue warnings about the former style (which can also occur on
choices), since it is so unintuitive.
But for PCAP, all the discrimnators have to change.
See: [https://github.com/DFDLSchemas/PCAP/issues/4]
was:
Daffodil should issue a warning, possibly even an SDE, about misplaced
discriminators:
I observed that many things with discriminators are coded like this:
```
<xs:sequence>
<xs:annotation><xs:appinfo source="http://www.ogf.org/dfdl/";>
<dfdl:discriminator ....../>
</xs:appinfo></xs:annotation>
....rest of sequence...
</xs:sequence>
```
So, it's quite unintuitive, but that discriminator will be executed AFTER the
rest of the sequence.
I'm not sure why we decided that is how DFDL should work, but to get the
discriminator to run BEFORE the rest of the sequence, which is typically what
you want from a discriminator, you must nest it within ANOTHER sequence inside
the first like so:
```
<xs:sequence>
<xs:sequence>
<xs:annotation><xs:appinfo source="http://www.ogf.org/dfdl/";>
<dfdl:discriminator ....../>
</xs:appinfo></xs:annotation>
</xs:sequence>
....rest of sequence...
</xs:sequence>
```
Daffodil issue warnings about the former style (which can also occur on
choices), since it is so unintuitive.
But for PCAP, all the discrimnators have to change.
See: https://github.com/DFDLSchemas/PCAP/issues/4
> Warning needed for misplaced discriminators
> -------------------------------------------
>
> Key: DAFFODIL-2277
> URL: https://issues.apache.org/jira/browse/DAFFODIL-2277
> Project: Daffodil
> Issue Type: Bug
> Components: Front End
> Affects Versions: 2.5.0
> Reporter: Mike Beckerle
> Priority: Major
> Fix For: 2.6.0
>
>
> Daffodil should issue a warning, possibly even an SDE, about misplaced
> discriminators:
> I observed that many things with discriminators are coded like this:
> ```
> <xs:sequence>
> <xs:annotation><xs:appinfo source="http://www.ogf.org/dfdl/";>
> <dfdl:discriminator ....../>
> </xs:appinfo></xs:annotation>
> ....rest of sequence...
> </xs:sequence>
> ```
> So, it's quite unintuitive, but that discriminator will be executed AFTER
> the rest of the sequence.
> I'm not sure why we decided that is how DFDL should work, but to get the
> discriminator to run BEFORE the rest of the sequence, which is typically what
> you want from a discriminator, you must nest it within ANOTHER sequence
> inside the first like so:
> ```
> <xs:sequence>
> <xs:sequence>
> <xs:annotation><xs:appinfo source="http://www.ogf.org/dfdl/";>
> <dfdl:discriminator ....../>
> </xs:appinfo></xs:annotation>
> </xs:sequence>
> ....rest of sequence...
> </xs:sequence>
> ```
> Daffodil should issue warnings about the former style (which can also occur
> on choices), since it is so unintuitive.
> But for PCAP, all the discrimnators have to change.
> See: [https://github.com/DFDLSchemas/PCAP/issues/4]
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