6.871, Spring 2005, Prof. Davis Transit Advisor Table of Contents 1. Introduction................................................................................................................................. 2 2. The Task....................................................................................................................................... 2 2.1. A Concrete Problem Example ......................................................................................... 3 2.2. Using the Transit Advisor program ................................................................................ 4 2.2.1. User Interface Symbols ............................................................................................ 4 2.2.2. Providing Scenario Input......................................................................................... 4 2.3. User Interface Shortcuts ................................................................................................... 5 3. Problem Solving Paradigm ........................................................................................................64. The Agents ................................................................................................................................... 8 4.1. Walking................................................................................................................................ 8 4.2. Biking................................................................................................................................... 8 4.3. Taxicab ................................................................................................................................ 9 4.4. Zip Car................................................................................................................................. 9 4.5. The T ................................................................................................................................... 9 5. Validation of the Problem Solving Principle (AKA “The Point™”)................................10 6. Limitations of Transit Advisor................................................................................................11 6.1. Extra Freedom .................................................................................................................11 6.2. Extra Constraints .............................................................................................................11 6.3. Scope of Information ......................................................................................................12 7. Reflections..................................................................................................................................12 7.1. What Went Well...............................................................................................................12 7.2. What Went Poorly & Lessons Learned ........................................................................12 8. Conclusion .................................................................................................................................13 9. Appendix – Knowledge Base ..................................................................................................14 9.1. XPortMode interface.......................................................................................................14 9.2. Walking..............................................................................................................................14 9.3. Biking.................................................................................................................................15 9.4. Taxicab ..............................................................................................................................16 9.5. ZipCar................................................................................................................................17 9.6. T .........................................................................................................................................19 Table of Figures Figure 1. Screenshot of a solution. Details are provided in the text ........................................... 3 Figure 2. Screenshot of a solution involving three modes of transportation.............................. 4 Figure 3. Flow diagram of questions asked to user and corresponding inferences made at beginning of execution. ....................................................................................................................... 5 Figure 4. Annotated illustration of greenboard/agent interaction................................................ 7 11. Introduction The Transit Advisor is a knowledge based system which constructs itineraries for travel around Boston and Cambridge. The program contains knowledge about many modes of transportation, organized with the blackboard and agent problem solving paradigm. Instead of embedding the transportation knowledge into search procedures (i.e. telling the program what to do), this architecture allows knowledge to be expressed in a very direct way (i.e. telling the program what to know). 2. The Task The Transit Advisor helps its user get from point A to point B within the Cambridge/Boston area. Its input is an origin, destination, and a set of ancillary inputs that tell the program what to know about available modes of transportation. The output of the program is an itinerary, with a low overall monetary and time cost (relative to all options), that will get the user from the origin to the destination. The program knows about and will consider walking, biking, taking a taxi, taking the T, or using a ZipCar. Each of these options has differentiating factors that make them appropriate in different situations. For example, the user cannot take the T or a ZipCar unless they move to any number of specific locations. Some modes of transportation have constant costs, like $1.25 to ride the T or a 3 minute wait for a taxicab. Each mode has a different speed, and can require you to go in a non-direct path (i.e. the T). Differences in cost, location, and speed make different modes of transportation appropriate in particular circumstances. The Transit Advisor evaluates all possible itineraries, and presents the best one to the user. This goal surfaces the question – what makes an itinerary good?