optionality of operation nodes in the interface et. al

Hi All,

Had a question on the WSDL 2.0 schema.
What is the reason for the optionality of "operation" nodes in an interface
? Similarly, the optionality of the input, output and faults for operations
etc ?
If I have an interface with no operation nodes within it, it wd be still
considered syntactically valid. [the behaviour is the same in WSDL
1.1schema as well].

rgds,
Menon
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