Safe interactions
Agents do not incur obligations by retrieving a representation.
Wrong to publish a link that, when followed, subscribes you to a mailing list or charges your credit card. Search engines and cache fillers may follow such links.
TAG finding URIs, Addressability, and the use of HTTP GET and POST gives specific guidance for safe and unsafe interactions.
XForms and SOAP encouraged to use GET for simple bookmarkable information retrieval. Interaction with security, structure and internationalisation (message bodies vs URI name-value pairs)
WSDL 2.0 Part 1: Core WD added a property called "safety" on interface operations.