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Re: RE : Comparison of Xml documents

• To: Alessandro Triglia <sandro@m...>
• Subject: Re: RE : Comparison of Xml documents
• From: Bob Foster <bob@o...>
• Date: Mon, 24 Nov 2003 19:56:17 -0600
• Cc: bob@w..., xml-dev@l...
• In-reply-to: <000601c3b299$a1496cb0$8d5d7ed2@aldebaran>
• References: <000601c3b299$a1496cb0$8d5d7ed2@aldebaran>
• User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.5) Gecko/20031007

Alessandro Triglia wrote:
> Bob,
> 
> As I said yesterday,

Sorry to make you repeat yourself.

> **Roughly speaking**, WXS "sequence"s are mapped to ASN.1 SEQUENCEs, while
> WXS "all"s are mapped to ASN.1 SEQUENCEs plus explicit information about the
> order.  The order is made a part of the abstract type definition and so is
> made available to the ASN.1 application.  
> 
> So, although ASN.1 lacks, per se, an equivalent of the WXS "all" model
> group, the ability to specify semantic significance in XML encodings (which
> means lexical "variable order", as opposed to "any order") is realized by
> writing something like the following:
> 
> -------------
> MyAll ::= [USE-ORDER] SEQUENCE {
>     order SEQUENCE OF ENUMERATED {a, b, c},
>     a     INTEGER (1..1000),
>     b     INTEGER (1..100),
>     c     UTF8String }
> -------------
> 
> This works as follows.  The abstract value:
> 
> v1 MyAll ::= { order {b, c, a}, 
>     a 1000,  b 70,  c "hello" }
> 
> is encoded in XML as:
> 
> -------------
> <v1>
>     <b>70</b>
>     <c>hello<c/>
>     <a>1000</a>
> </v1>
> -------------
> 
> The abstract value:
>   
> v2 MyAll ::= { order {c, a, b}, 
>     a 1000,  b 70,  c "hello" }
> 
> is encoded as:
> 
> -------------
> <v2>
>     <c>hello<c/>
>     <a>1000</a>
>     <b>70</b>
> </v2>
> -------------
> 
> In this way, even if the constructor is SEQUENCE (and not "ALL"), the
> information about the order is present in the abstract value, and is
> therefore accessible by the application, both when writing and when reading
> the abstract instance.
> 
> In other encoding rules the SEQUENCE OF ENUMERATED is encoded as a normal
> SEQUENCE OF, because there is no requirement for the "lexical order" to be
> implemented as physical lexical order.  Notice that it is always the same
> information, which may be "encoded" either as a physical order of child
> elements (in XML), or explicitly as a SEQUENCE OF ENUMERATED (in other
> encoding rules).

I was rolling right along with you until now. (I know I'm in trouble 
when I don't understand either sentence of a two-sentence paragraph.)

First things first, Encoding aside, do applications exchange abstract 
values? In other words, is the value:

 > v2 MyAll ::= { order {c, a, b},
 >     a 1000,  b 70,  c "hello" }

Recieved at the other end as a sequence of (c, a, b), i.e., in that 
order, or not?

Thanks again.

Bob Foster

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