What is the difference between Type and Element in WSDL?

Question

In WSDL file a function can return a Type or an Element. I have used only custom types as a results so far. However, I wonder when the Element should be more appropriate then the Type? What is the difference between them?

Is there any difference between

<wsdl:message name="MyFunction">
    <wsdl:part name="parameters" element="tns:Person"></wsdl:part>
</wsdl:message>

and

<wsdl:message name="MyFunction">
    <wsdl:part name="parameters" type="tns:Person"></wsdl:part>
</wsdl:message>

from a Client perspective (application that make use of the web service)?

The above question, as skaffman pointed, leads to a another question. What is the difference between

<xs:element name="Person" ... >
 ...
</xs:element>

and

<xs:complexType name="Person">
   ...
</xs:complexType>

?

Answer 1

Which one you use depends on the schema to which it is referring. If tns:Person is defined in the schema as:

<xs:element name="Person" ... >
 ...
</xs:element>

Then you use

<wsdl:part name="parameters" element="tns:Person">

If, on the other hand, the schema is defined as

<xs:complexType name="Person">
   ...
</xs:complexType>

then you use

<wsdl:part name="parameters" type="tns:Person">

So the question is really what's the difference between Schema elements, and Schema types.

Answer 2

I cannot comment on the WSDL part of the question, but I'll answer the XML Schema part.

<xs:complexType> defines a type, which describes content of an element, without describing the element itself (i.e. its name). <xs:element> describes an element (specifically its name), but not its type. However, <xs:element> always references the type for the content of the element it describes. This can be a reference to an existing type (including, but not limited to, <xs:complexType> - it can also be <xs:simpleType>, for example) definition elsewhere in the schema, or an inline <xs:complexType> definition:

<xs:element name="foo">
   <xs:complexType>
      ...
   </xs:complexType>
</xs:element>

Since the above construct is so common, you can actually omit <xs:complexType> entirely, and it will be implied.

As for whether you should always define types separately and then reference them in element declarations, or whether you should prefer defining element types inline within element declarations, it is a matter of style.