The WSDL xml interface is generated by Identity Manager based on the configuration and settings of the IDM tasks which are enabled for web services.
Each attribute on a task is translated to a "Element" in the wsdl interface. On the XML element tag there are properties.
One of these properties is called: "minOccurs". This property indicates to the web service the minimum number of occurrences this element must be included in the SOAP request of that particular task. When generating the interface this property will be explicit on each element with a value of '0'. This suggests it's not a mandatory field and is optional on the SOAP request.
Release: All Identity Manager's environments.
Below is an excerpt of a Modify User profile tab wsdl interface. If you wanted to ensure that Full Name will be mandatory for web service call submissions then you shall make sure that minOccurs="1" is marked for that field. In the example below you can see this being the case for the Full Name attribute (which is the last in that excerpt).
<xs:element name="ViewandModifyUserProfileTab">
If a field is mandatory on the task (for example: Read/Write Required) then this property is omitted from the 'Element' tag. By this omission this attribute is now becoming mandatory for the SOAP xml request.