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From a SOAP perspective, the distinction is whether or not you are using the
SOAP RPC programming convention, as described in Section 7 of the SOAP 1.1
specification or Section 5 of the SOAP 1.2 Part 2 specification. This RPC
programming convention is designed to allow SOAP to emulate an RPC call,
i.e., to invoke a method using a method name and some set of parameters (0
or more), which returns a return value and some set of parameters (0 or
more). From a wire perspective, a SOAP message body that's constructed using
the RPC programming convention passes structures rather than individual
elements. The request message (method invocation) is a modeled as a single
struct, which contains an accessor for each [in] and/or [in/out] parameter.
The name and type of the struct corresponds to the name and type of the
method, and the name and type of each accessor corresponds to the name of
each parameter. Likewise, the response message is modeled as a single struct
containing an accessor for the return value (always the first accessor) and
each of the [out] and/or [in/out] parameters. The name and type of each of
the response accessors must match the name and type of the return
parameters. When not using the RPC programming convention (usually referred
to a SOAP Messaging), the message body may contain any number of elements.
These elements normally conform to a schema of some sort, so a lot of folks
characterize SOAP messaging by saying that you are passing "documents".
The terms "RPC-oriented" and "Document-oriented" are artifacts of the WSDL
specification. To quote Section 3.4 of the WSDL 1.1 specification, "The
style attribute [in the WSDL soap:operation element] indicates whether the
operation is RPC-oriented (messages containing parameters and return values)
or document-oriented (messages containing document(s)). This information may
be used to select an aproriate programming model. The value of this
attribute also affects the way in which the BODY of the SOAP message is
constructed." [the message construction bit refers to the struct structure
defined in the SOAP spec.] Keep in mind that if no value is specified, the
default value is "document".
So -- this seems pretty straightforward. If you're invoking methods, you
should be using the RPC programming convention, and you should describe your
operations in WSDL as RPC-style. But it's not quite as simple as that. You
can describe a SOAP message that uses the RPC programming convention as a
document-style operation. And, in fact, Microsoft SOAP does so by default.
This particular feature causes a fair amount of trouble when it comes to
making .NET interoperate with other SOAP implementations. For easier
interoperability, I'd recommend that you add the [SoapRpcService] directive
to your applications to tell MS SOAP to define the service as RPC style,
e.g.:
<%@ WebService Language="C#" Class="MSNetStockService" %>
using System.Web.Services;
using System.Web.Services.Protocols;
using System.Web.Services.Description;
[SoapRpcService]
public class MSNetStockService {
[WebMethod] ..
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