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   RE: [xml-dev] SAX for Binary Encodings (preserving investment) (ASN.1 an

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I wrote:
> Bob Wyman wrote:
> > 
> > I argue that if something is
> > marked to be an attribute when converted to XML, then it 
> > should be marked as an attribute when it is passed through an 
> > interface like SAX which is commonly used to process XML-like 
> > data. If this were not the case, then binary data would look 
> > different to the user of SAX when it was read directly via 
> > SAX rather than being read from a chunk of XML written by the 
> > XML encoder. This would be silly and unproductive.
> I absolutely agree.  Another way of saying this is that the 
> stream of SAX
> callbacks coming from parsing/decoding an encoding of ASN.1 (BER, PER,
> EXTENDED-XER) has to be exactly the same stream, for a given 
> schema and a
> given instance, regardless of the encoding rules in use (BER, PER,
> EXTENDED-XER), and has to be the same stream as would be 
> generated by a
> "normal" SAX parser parsing the XML document.  It must be possible to
> replace a normal SAX parser used by an application with an ASN.1
> parser/decoder for either XML or binary encodings with 
> minimum changes to
> the application code.  This will give us the interoperability we need
> between the two worlds.

And it is not just about attributes vs. elements.  It is also about: 

- mixed content,

- variable-order sequences (those consisting in a group of elements whose
order in the instance "doesn't matter" (*)), 

- removing wrappers around multiple occurrences of things,

- CHOICEs corresponding to XSD's type derivation hierarchies,

- CHOICEs corresponding to XSD's element substitution groups,

- CHOICEs corresponding to XSD's unions,

- "SEQUENCE OF"s corresponding to XSD's lists,

- support of wildcards,

and so on.

All these features (and others) are supported by an XER-specific notation in
the ASN.1 schema, which affects EXTENDED-XER encodings but does not affect
BER/PER encodings.  However, a SAX XMLReader over BER/PER should behave *as
if* BER/PER encodings contained some representation of the above things as

Alessandro Triglia

(*) or "matters", depending on people's views and use cases (ASN.1 supports
both views/use cases).

> Alessandro Triglia
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