for all s', r, s, and a, The Markov Property is guaranteed if the state representation encodes everything that the system has been able to observe about everything that happened in the dialogue so far However  this representation would be too complex to estimate a model of the probability of various state transitions  and systems as complex as spoken dialogue system must in general utilize state representations which are as compact as possible 2 However if the state representation is too impoverished the system will lose too much relevant information to work well

| Operations Variable     | Abbrev     | Possible Values   |             |             |     |
|-------------------------|------------|-------------------|-------------|-------------|-----|
| Know User Name          |            |                   |             |             |     |
| InitStrat               | SI MI      |                   |             |             |     |
| S SCP SB                |            |                   |             |             |     |
| Summ Strat              | s          |                   |             |             |     |
| ReadStrat               | RF RSO RCP |                   |             |             |     |
| R                       |            |                   |             |             |     |
| TaskProgress            |            |                   |             |             |     |
| Current User Goal       | G          | Read Summarize    |             |             |     |
| NumMatches              | M          | N                 |             |             |     |
| WhichSelection          | W          | Sender            | Snd Subject | Sub InOrder | InO |
| Know Selection Criteria | SC         |                   |             |             |     |
| Confidence              | C          |                   |             |             |     |
| Timeout                 |            |                   |             |             |     |
| Help                    |            |                   |             |             |     |
| Cancel                  |            |                   |             |             |     |

Figure Operations variables and possible values that define the operations vector for controlling all aspects of ELVIS s behavior The abbreviations for the variable names and values are used as column headers for the Operations Variables in Figures and ELVIS s state space representation must obviously discriminate among states in which various strategy choices are explored but in addition there must be state variables to capture distinctions between a number of states in which ELVIS always executes the same strategy The state variables that ELVIS keeps track of and their possible values are given in The KnowUserName  U  variable keeps track of whether ELVIS knows the user s Figure nme or not The InitStrat I SummStrat S and ReadStrat R variables keep track of whether Elvis has already employed a particular initiative strategy summarize strategy or a reading strategy in the current dialogue and if so  which strategy it has selected This variable is needed because once ELVIS employs one of these strategies that strategy is used consistently throughout the rest of the dialogue in order to avoid confusing the user The TaskProgress P variable tracks how much progress the user has made completing the experimental task The CurrentUserGoal G  variable corresponds to the system s  belief