Instances of Visibility could be “Public”, “Acme Inc Enterprise-Wide”, “Members of soa-ontology mail list”, etc. An Actor can be a person or an organization or a piece of technology – someone or something that does something A Policy is owned and operated by a single party A Service represents a particular, described, pattern of behavior, such as “haircut”; not an instance - not “the haircut that I had yesterday” A Contract is agreed between two or more parties Not needed for all viewpoints Not just a transient property - includes 'consumes at this instant', has 'consumed', and 'may in future consume' Not just a transient property - includes 'provides at this instant', has 'provided', and 'may in future provide' A policy specifies a particuar visibility for any particular description - but may specify multiple visibilities, because it may refer to multiple descriptions. A registry provides a visibility if any of the descriptions contained in it have that visibility. A description of a particular service with a particular visibility. Need not completely describe the service - multiple descriptions may be needed to describe the service fully. Is contained in at most one registry. Different registries may contain equivalent descriptions - possibly with different visibilities. A registry may contain non-equivalent descriptions of a service, possibly with different visibilities.