17. The method of claim 15 , further comprising providing a list comprising said second set of entities to a user.
15. A method comprising: receiving registrations from a first set of entities of a plurality of entities, each registration representing presence of a respective entity in said first set; receiving items of information descriptive of contexts associated with each entity in said first set of entities, wherein said contexts comprises first information comprising information other than locations of said entities in said first set, wherein said first set information comprises an entity-specific value for a quantifiable and variable property associated with said entities in said first set; receiving a request to identify which of said entities in said first set has a value for said property that satisfies a specified criterion, wherein said request further comprises a context, wherein said context comprises second information other than location information that generally describes a targeted entity but does not specifically identify said targeted entity and wherein a message is associated with said context; based on said registrations, said first information, and said second information and in response to said request, searching said first information and ascertaining a second set of entities selected from said first set, wherein entities contained in said second set have a value for said property that satisfies said criterion, wherein each of said entities in said second set is associated with an identifier comprising unique contact information for each entity in said second set; and providing identification of said second set of entities and said identifier for each entity in said second set, wherein in response to said identification being received, said message is automatically delivered to said second set of entities; wherein said context comprises descriptions of locations of said entities, wherein said context comprises a description of a geographic position, wherein said service module ascertains said one or more of said entities based on which of said entities' description of location satisfies a positional predicate with respect to the geographic position described in said context.