From my experience, with SOA Retail solutions the following SOA Guiding Principles have served us well. We have applied this "standard" to both internal SOA style business services and when evaluating other packaged products that claim to be "SOA Enabled"!!!
a) business service consumers are decoupled from business service providers.
b) availability of published "service metadata" enables the discovery of the business service.
c) service consumers are agnostic of who (service provider location) and how (service provider technology platform) the function call is being fulfilled.
d) service consumers and service providers that use industry standard protocols and communications models are able to insure loose coupling.
e) service interaction is based upon exchange of canonical models
Please provide me with your feedback.