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On 15-Jan-2001, Ina Cheng <in...@st...> wrote:
> Hi Tyson,
> 
> In the example of the SOAP spec
> 
> <SOAP-ENV:Envelope
>  xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"
>  SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">
>  	<SOAP-ENV:Body>
>   	 <m:GetStockPrice xmlns:m="some uri">
> 	   <symbol>DIS</symbol>
>   	 </m:GetStockPrice>
>  	</SOAP-ENV:Body>
> </SOAP-ENV:Envelope>
> 
> The paper said the request takes a string parameter, ticker symbol and 
> returns a float etc. 
> 
> How can I be sure that `DIS' is of type string and not other type?

Ah, this is where the research part of your project starts.

The SOAP spec says (section 5)

	First, given a schema in any notation consistent with the type
	system described, a schema for an XML grammar may be
	constructed.  Second, given a type-system schema and a
	particular graph of values conforming to that schema, an XML
	instance may be constructed. 

This means given a Mercury value (== graph of values conforming to that
schema) and a system for converting Mercury types to XML, you can create
an XML document.

	In reverse, given an XML instance produced in accordance with
	these rules, and given also the original schema, a copy of the
	original value graph may be constructed.

This says that you can reverse it and get back the original Mercury
value from the XML document (plus the schema you used to generate it).

But this doesn't answer your question -- it just allows us to understand
this paragraph (5.1)

	Although it is possible to use the xsi:type attribute such that
	a graph of values is self-describing both in its structure and
	the types of its values, the serialization rules permit that the
	types of values MAY be determinate only by reference to a
	schema. Such schemas MAY be in the notation described by "XML
	Schema Part 1: Structures" [10] and "XML Schema Part 2:
	Datatypes" [11] or MAY be in any other notation. Note also that,
	while the serialization rules apply to compound types other than
	arrays and structs, many schemas will contain only struct and
	array types.

So, either you:
	- embed xsi:type attributes on each node that says what type this
	  node is.
	- assume that some agreed upon schema is used to describe the
	  values (and the rest of this section is an example/suggestion of 
	  such a schema).

Now they say "schema" as a generic term for any sort of systematic
transformation, but they also suggest using XML Schema (which aren't yet
standard).  The example they give is pretty close to XML Schema. 

So later on there is an example schema:

	<element name="age" type="int"/>
	<element name="height" type="float"/>
	<element name="displacement" type="negativeInteger"/>
	<element name="color">
		<simpleType base="xsd:string">
		<enumeration value="Green"/>
		<enumeration value="Blue"/>
		</simpleType>
	</element>

Which could be used to describe the following instances:

	<age>45</age>
	<height>5.9</height>
	<displacement>-450</displacement>
	<color>Blue</color> 

Now if you (somehow) had that schema, it would be pretty easy to figure
it out and do the conversion in either direction.

So perhaps you can find a place to slot this schema into the
implementation (e.g. you have to provide one for each method that is
exposed in the web server).  And you can assume that the caller
has a copy of it too (they will use it to generate their SOAP message).

I think that IBM's Web Services are an attempt to provide this
information "on-the-fly" -- e.g. if you want to use SOAP for RPC, it
will provide you with a schema which you can download first, then you
can use the SOAP message to do the call.

Certainly this is a point where the SOAP spec takes a hands-off approach
-- each implementation can make its own decisions here.

But you might want to read up on this a bit further and let me know what
you find.

> 
> Can I assume if the argument is of type int, the soap message will be something
> like:
> 
> 	<int> 1 </int>  ?

This is pretty similar to the case of embedding the type, it would
probably look more like:

	<cost xsi:type="xsd:float">29.95</cost>

or
	<SOAP-ENC:int id="int1">45</SOAP-ENC:int>

-- 
       Tyson Dowd           # 
                            #  Surreal humour isn't everyone's cup of fur.
     tr...@cs...        # 
http://www.cs.mu.oz.au/~trd #

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