> If you don't know the initiators, but know what is coming next

I get your solution, and it looks useful, but…email headers can arrive in any order (excepting a couple headers, like Received, which are supposed to be first).

So I could get: To, From, Keywords, Subject

Or I could get: Keywords, To, Subject, From

Or I could get any other combination.

If the order is not known a priori, can I still use this approach?

How about something like this (pseudo code)?

HeaderArray (0 to unbounded)

Sequence

From

Subject

UnwantedHeader (ref to the Group)

/Sequence

/HeaderArray

Group (see the group Steve defined below)

The problem, of course, is that I don’t know what the Header keys will be. Can I have a whole bunch of discriminators, one for every *allowed* header? IOW, the discriminator is “any header that’s not one of the headers that I want.”

From: Steve Hanson [mailto:smh@uk.ibm.com]
Sent: Friday, March 01, 2013 9:03 AM
To: Garriss Jr., James P.
Cc: dfdl-wg@ogf.org; dfdl-wg-bounces@ogf.org
Subject: Re: [DFDL-WG] Can I ignore data I don't want in DFDL?

The general solution in DFDL is to use the combination of an optional repeating element inside a hidden group.

You need to be careful that this optional hidden element does not consume the next piece of wanted data by mistake. If all the unwanted elements have known initiators then you are ok. If you don't know the initiators, but know what is coming next, then one approach is as follows:

<xs:complexType>
<xs:sequence>
<xs:element name="From" type="NameType" dfdl:initiator="From:%WSP*;" terminator="%NL;%WSP*;" />
<xs:element name="To" type="NameType" dfdl:initiator="To:%WSP*;" terminator="%NL;%WSP*;"/>
<xs:sequence dfdl:hiddenGroupRef="UnwantedGroup" />
<xs:element name="Subject" type="xs:string" dfdl:initiator="Subject:%WSP*;" terminator="%NL;%WSP*;"/>
</xs:sequence>
</xs:complexType>

<xs:group name="UnwantedGroup>
<xs:sequence>
<xs:element name="UnwantedHeaders" maxOccurs="unbounded" />
<xs:complexType>
<xs:sequence>
<xs:element name="Unwanted" type="xs:string" terminator="%NL;%WSP*;">
<xsd:annotation><xsd:appinfo source="http://www.ogf.org/dfdl/">
<dfdl:discriminator test="{fn:not(fn:startWith("Subject:"))}"/>
</xsd:appinfo></xsd:annotation>
</xs:element>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>

The hidden loop should consume all header lines that do not start with "Subject:" and stop when it reaches one that does.

I've used a terminator for the header lines, you may have used a separator with separatorPolicy 'suppressed'. Either should work, but the terminator gives you the opportunity to handle data where the final CRLF is missing (via property dfdl:documentFinalTerminatorCanBeMissing).

Regards

Steve Hanson
Architect, Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh@uk.ibm.com
tel:+44-1962-815848

From: "Garriss Jr., James P." <jgarriss@mitre.org>
To: "dfdl-wg@ogf.org" <dfdl-wg@ogf.org>,
Date: 01/03/2013 13:15
Subject: [DFDL-WG] Can I ignore data I don't want in DFDL?
Sent by: dfdl-wg-bounces@ogf.org

Suppose I am using DFDL to parse email headers. Suppose the RFC only allows 3 headers: To, From, Subject. DFDL can handle this, no problem.

But suppose I get an email that includes a 4th header, one I have not planned for (i.e., have not included in the DFDL schema), don’t care about, and don’t want in the infoset. Like so:

From: <john@doe.com>
To: <jane@doe.com>
Keywords: sales <-- this line should be ignored!
Subject: Latest sales figures

Can DFDL handle this? Does it have a mechanism for allowing me to ignore (and thus drop) data I haven’t planned for and don’t care about?--
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