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Re: XML encoding ASN.1 (was Re: Another Question)

• From: "Peter Jacobi" <pj@w...>
• To: Olivier.Dubuisson@f...
• Date: Thu, 22 Jun 2000 16:09:33 +0200

Olivier, All,

> > a) use the tags as element names ("A17" for [APPLICATION 17]),
> > use fixed attributes for identifiers and data type names.
> 
> Tags are historical "residues" in ASN.1. They are only used by the
> BER encoding rules.
> It is now recommended to add the "AUTOMATIC TAGS" clause in the
> module headers and to not take core of the tags any more.

Even when AUTOMATIC TAGS  is used, each element has a tag. 
And there seems to be an argument for tags, as can be seen by the wide 
selection of file formats using some sort of tagging, to be extensible (e.g. 
MPEG).

> > b) use the identifiers as element names, use fixed attributes for tags
> > and data type names.
> 
> What's the need to keep the tags and type names? It seems to me that
> this verbosity is useless.

In the normal case, no verbosity is involved, as fixed attributes aren't 
transmitted in the document instances.

> Do you make the assumption that both sides (i.e., the encoder and the
> decoder) are generated from the same ASN.1 module? 

Yes, but I want to be prepared for extensions. That's the main reason 
you cannot drop the tag, as that would prohibit round-tripping BER-
>XMLencoding->BER.

The original sender may use a special tag value to insert an element into 
a SEQUENCE. You must keep this tag value in the XML encoding for the 
sahe of re-producing a BER encoded version.

Regards,
Peter Jacobi


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  • Re: XML encoding ASN.1 (was Re: Another Question)
    • From: Olivier DUBUISSON <Olivier.Dubuisson@f...>

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