30. The apparatus according to claim 18 , wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to at least: access the one or more rules written in a microplanning rule specification language by a user via the user interface; and convert the one or more rules into the set of lexicalization comprising the set of message-level rules and the set of slot-level rules.
18. An apparatus that is configured to transform an input data stream comprising data that is expressed in a non-linguistic format into a format that can be expressed linguistically in a textual output, the apparatus comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to at least: access a document plan containing one or more messages, wherein messages represent a phrase or a simple sentence and are created in an instance in which the input data stream comprises data that satisfies one or more message requirements; generate a text specification containing one or more phrase specifications that correspond to the one or more messages in the document plan; apply a set of lexicalization rules to each of the one or more messages to populate the one or more phrase specifications, wherein the set of lexicalization rules are specified using a microplanning rule specification language that is configured to hide linguistic complexities from a user and comprise a set of message-level rules and a set of slot-level rules; and realize the text specification to generate a textual output that linguistically describes at least a portion of the input data stream, wherein the textual output is displayable via a user interface.