Communication Aspects: How Landmarks Enrich the Communication Between Human and Machine - Landmarks: GIScience for Intelligent Services - page 176

Fig. 6.1 Thearchitectureof
the CORAL system
(after [ 17 ] )

Path-based
Route Plan

Text Planner

Message
Sequence

Microplanner

Sentence
Plans

Surface Realizer

Text

that gets away from the one-sentence-per-step messages routing services produce,
and instead make use of more complex clause structures that cover related infor-
mation in a single sentence. Their CORAL system generates such instructions; its
architecture is shown in Fig. 6.1 . This kind of architecture is quite typical for NLG-
motivated route planners and reflects to a degree the theoretical models for giving
route directions discussed in Sect. 3.4 .
CORAL starts out with a route through a network representation of the environ-
ment, very similar to what is used in any routing service. It then moves through
three phases to arrive at the verbal messages communicated to the user. The
first phase, the text planner , determines what information about the route needs
to be conveyed. This information is represented using three different message
types: POINT messages refer to landmarks (e.g., 'turn left at the gas station ');
DIRECTION messages correspond to turns made at decision points (e.g., 'turn
right'); PATH messages describe continuous movement along parts of the road
network (e.g., 'follow the road'). The text planner phase results in an alternating
sequence of POINT, DIRECTION, and PATH messages, finishing with a POINT
message that describes the destination.
This text plan is the input for the micro-planning phase, which decides how to
combine the individual messages into clause structures and also how to refer to
each of the referenced elements. The former is an aggregation task, where two