Web Service: Single String Parameter Or Complex Type Parameters

Question

Is it more or less acceptable (i.e. standard) to create a publicly-exposed web service with these method signatures:

ThisMethodDoesSomething(ComplexType param)

ThisMethodDoesSomethingElse(AnotherComplexType param)

Or this:

ThisMethodDoesSomethingAndSomethingElse(string xml)

Where the operation being performed depends upon the XML string passed to a single does-it-all method? I have always gone with the former, but a coworker of mine prefers the latter and I'm trying to weigh pros and cons of both strategies before we begin a new project. Which is more accepted and easier for the public to work with and why?

Answer 1

I would never send an XML string. First of all, "XML" is not the same thing as "string". They do not follow the same rules.

Any reasonable client can accept a complex type consisting of primitive types and lists or arrays of primitive types, recursively (C# syntax):

public class ComplexType1
{
    public int IntegerProperty {get;set;}
    public int[] ArrayOfIntegers {get;set;}
    public List<int> ListOfIntegers {get;set;} // Same as ArrayOfIntegers
}

public class ComplexType2
{
    public ComplexType1 CT1 {get;set;}
    public List<ComplexType1> LCT1 {get;set;}
}

Frankly, any client that can't deal with something like the above deserves to be retired.

Answer 2

Formerly I would have prefered the latter, because I wasn't sure, if in cross platform situation, every SOAP client would be able to consume the complex types properly. So I thought a SOAP call, that just takes and returns (XML-)Strings will give me no headache. In the meantime I experienced there is generally no problem with the first approach at least for .Net interoperating with JAVA/AXIS and vice versa. I'm still watching to make the complex type not too complex though.

I assume that ThisMethodDoesSomething() and ThisMethodDoesSomethingElse() are atomic operations? If this not the case (ThisMethodDoesSomethingElse() requires a call to ThisMethodDoesSomething() to execute), the first approach is a no go.