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Robert Cemper · Dec 7, 2017

If your connection is not stable enough I'd suggest to take a closer look to good old Shadowing.

It's really jungle proof.
I used it in past to transfer data from an oil drill platform  somewhere out on the ocean over a satellite link with just 64k bd bandwidth without any data loss. And this link was far from whatever you would expect from a wired connection on ground.
Shadowing did id with incredible stability and no loss.
Cascading of shadowing is also almost unlimited with no  issue. 
 

Robert Cemper · Nov 30, 2017

Example WebService:

/// My.SOAP
Class My.SOAP Extends %SOAP.WebService [ ProcedureBlock ]
{

/// Name des WebService.
Parameter SERVICENAME = "MyService";

/// SOAP Namespace für den WebService
Parameter NAMESPACE = "http://tempuri.org";

/// Namespaces von referenzierten Klassen werden in der WSDL verwendet.
Parameter USECLASSNAMESPACES = 1;

Method GetCustomerInfo(schema1 As My.Schema1) As My.Schema2 [ WebMethod ]
{
 set max   =schema1.MaxResult
    ,home  =schema1.HomeState
    ,office=schema1.OfficeState
    ,start =schema1.NameStartswith
 set:'max max=1
 set:office="" office=home
 set schema2=##class(My.Schema2).%New()
    ,rs=##class(%ResultSet).%New()
    ,sql="SELECT top ? %ID FROM Sample.Employee "
        _"WHERE Home_State = ? "
        _"AND Office_state = ? "
        _"AND Name %STARTSWITH ? "
       ,tSC=rs.Prepare(sql)
 set:tSC tSC=rs.Execute(max,home,office,start)
 while rs.Next()&&tSC {
   set employee=rs.GetObject()
      ,res=##class(My.Schema2Result).%New()
      ,res.HomeAddress=employee.Home
      ,res.OfficeAddress=employee.Office
      ,res.Name=employee.Name
      ,res.pid=employee.%Id()
   do schema2.Results.Insert(res)
  }
 quit schema2
}
}
Robert Cemper · Nov 30, 2017

Example Schema1
<?xml version="1.0" encoding="UTF-8"?>
<s:schema xmlns:s="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified" attributeFormDefault="unqualified">
<s:complexType name="Schema1">
    <s:sequence>
        <s:element name="Max_Results">
            <s:simpleType>
                <s:restriction base="s:long">
                    <s:minInclusive value="1"/>
                </s:restriction>
            </s:simpleType>
        </s:element>
        <s:element name="Home-State">
            <s:simpleType>
                <s:restriction base="s:string">
                    <s:maxLength value="2"/>
                    <s:minLength value="2"/>
                </s:restriction>
            </s:simpleType>
        </s:element>
        <s:element minOccurs="0" name="Office-State" type="s:string"/>
        <s:element minOccurs="0" name="Name-Startswith" type="s:string"/>
    </s:sequence>
</s:complexType>
</s:schema>

Robert Cemper · Nov 30, 2017

Example Schema2

<?xml version="1.0" encoding="UTF-8"?>
<s:schema xmlns:s="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified" attributeFormDefault="unqualified">
    <s:complexType name="Schema2">
    <s:sequence>
        <s:element minOccurs="0" name="Results" type="ArrayOfSchema2Result"/>
    </s:sequence>
</s:complexType>
<s:complexType name="ArrayOfSchema2Result">
    <s:sequence>
        <s:element maxOccurs="unbounded" minOccurs="0" name="Schema2Result" nillable="true" type="Schema2Result"/>
    </s:sequence>
</s:complexType>
<s:complexType name="Schema2Result">
    <s:sequence>
        <s:element minOccurs="0" name="Home-Address" type="Address"/>
        <s:element minOccurs="0" name="Office-Address" type="Address"/>
        <s:element minOccurs="0" name="Person-Name" type="s:string"/>
        <s:element minOccurs="0" name="Person-ID" type="s:long"/>
    </s:sequence>
</s:complexType>
<s:complexType name="Address">
    <s:sequence>
        <s:element minOccurs="0" name="Street">
            <s:simpleType>
                <s:restriction base="s:string">
                    <s:maxLength value="80"/>
                </s:restriction>
            </s:simpleType>
        </s:element>
        <s:element minOccurs="0" name="City">
            <s:simpleType>
                <s:restriction base="s:string">
                    <s:maxLength value="80"/>
                </s:restriction>
            </s:simpleType>
        </s:element>
        <s:element minOccurs="0" name="State">
            <s:simpleType>
                <s:restriction base="s:string">
                    <s:maxLength value="2"/>
                </s:restriction>
            </s:simpleType>
        </s:element>
        <s:element minOccurs="0" name="Zip">
            <s:simpleType>
                <s:restriction base="s:string">
                    <s:maxLength value="5"/>
                </s:restriction>
            </s:simpleType>
        </s:element>
    </s:sequence>
</s:complexType>
</s:schema>
 

Robert Cemper · Nov 30, 2017

You may take this approach:

create an object based on Schema1: My.Schema1
create an object based on Schema2: My.Schema2

HowTo: => XML Schema Wizzard 
http://docs.intersystems.com/latest/csp/docbook/DocBook.UI.Page.cls?KEY=...

Then you may use this method.

Method GetCustomerInfo(schema1 as My.Schema1) As My.Schema2 [WebMethod]


My.Schema1 is checked as input parameter according tothe generated class
inside your Method you transform it to My.Schema2
and return it. 

The most tricky thing might be how to reply to a request that doesn't match Schema1.

Robert Cemper · Nov 29, 2017

I'm not an expert on callout but deep back in history I believe to remember that what ever you
transfer is in wider sense a single item. If string structured by $p() or $lb().
You my take a closer look to %XML.SAX.* classes.
The highest structure is $LB(). Which is a string under cover.
And take care of the 32k limit 

Robert Cemper · Nov 27, 2017

I'd suggest to use $LB() if you are not hit by the LongString limit.

why: all packaging, selection,.... is already done and "hard wired" in C++ 
with $C() you may re-invent $LB() or $Piece() or similar. And you have to do it in COS.
Same applies to local array where  you may iterate over the structure in COS again.

Nothing against COS but C++ (in COS Functions) IS faster