1. A natural language generation method for generating a referring noun phrase for an intended referent found in one or more messages within a document plan, the method comprising: arranging, using a processor, one or more messages in a document plan, wherein messages represent a phrase or a simple sentence and are created in an instance in which an input data stream comprises data that satisfies one or more message requirements, and wherein at least a portion of the input data stream comprises non-linguistic data; identifying an intended referent in a message of the one or more messages to be referred to in a textual output; determining a lowest common ancestor for the intended referent and a previously referred-to entity within a part-of hierarchy; determining a salient ancestor of the intended referent within the part-of hierarchy; generating a referring noun phrase for the intended referent to be included in a textual output by traversing the part-of hierarchy from the salient ancestor to the lowest common ancestor such that a default descriptor is added to a queue for at least a portion of entities traversed in the part-of-hierarchy, wherein the reference noun phrase comprises a default descriptor of the intended referent and one or more default descriptors of one or more parts of the part-of hierarchy that are traversed; generating the textual output comprising the referring noun phrase such that it is displayable on a user interface, wherein the textual output linguistically describes at least a portion of the input data stream; and displaying the textual output via a display device.
3. A method according to claim 1 , further comprising: determining that the intended referent is marked as salient; and causing the referring noun phrase to solely comprise the default descriptor of the intended referent.