We deliberately choose the constrained domain of bus information for our domain, so that we can better control the low level aspects of information presentation rather than be distracted with the higher level problems in dialog control. However, although apparently simple at first, there are still a number of issues in the bus information domain that must be addressed.
Naming a bus stop appears simple at first but more complex as you look closer at the system. Users may employ a wide range of phrases to refer to bus stops, and we wish to make the system deal with this. Although there are problems in abbreviation expansion, and typos in the core data, the idea of a canonical name for a bus stop is fairly well defined. ``Murray at Forward'' refers to the stop on Murray Avenue where it meets Forward Avenue. However there may be multiple stops at a crossroads that have different names. ``South Craig at Forbes'' is not the same bus stop as ``Forbes at South Craig'', though a human user is likely to conflate these as ``Forbes and Craig''.
Our initial system offers a number of rule-derived alternative names for stops but this will be insufficient in a general system. Thus we are investigating methods to give more general matches of user-given names to bus stops, which must also be efficient. For example ``Forbes'' (a major thoroughfare in Pittsburgh) has many stops and is used by many routes, thus ``Forbes'' alone seems insufficient to identify a stop. But the 54C routes have only one stop on Forbes, and thus it is possible to refer to that stop in the context of the 54C: ``from East Carson and 22nd to Forbes''
SYSTEM: Welcome to the CMU Let's Go! Bus Information System. How may I help you? USER: I'd like to go to Forbes and Murray. SYSTEM: To Forbes and Murray. Where are you leaving from? USER: Carnegie Mellon. SYSTEM: From Carnegie Mellon. There are five buses running between Carnegie Mellon and Forbes and Murray: the 501, the 59U, the 61A, the 61B, and the 61C. What else can I do for you? USER: When is the next one? SYSTEM: The next 61C going to Forbes and Murray will leave Carnegie Mellon at 5:13 PM.Figure 2: Example of a Let's Go dialog