Marking Operations as Safe

"Safe": requester agent incurs no obligation beyond invoking the operation
- Analogous to HTTP GET
- Can be implemented by with SOAP 1.2's SOAP-Response MEP or HTTP GET
Permits:
- Pre-fetch
- Re-fetch
- Safe exploration

<operation name="location" safe="true"
           pattern="http://www.w3.org/2004/08/wsdl/in-out">
  <input element="s:location"
    style="http://www.w3.org/2004/08/wsdl/style/uri-style"/>
  <output element="s:temperature"/>
</operation>