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V E N D O R   Q U E S T I O N S
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The Vendor Elicitor algorithm generates questions about available
vendors, items offered by each vendor, and their costs. Currently, it
uses the following question types.


FIND ADDITIONAL VENDORS

The system asks this question when the vendor list appears incomplete;
it is an unspecific request to find more vendors. The system generates
this request only when the "All Vendors" flag is "false."


FIND VENDORS WHO OFFER <ITEM-TYPE> OR ... OR <ITEM-TYPE>
[ WITH COST BELOW <UNIT-COST> ]

The system asks this question when it needs to satisfy some service
property, and either it has no information about vendors that offer
matching items, or all known offers are too expensive. Note that the
specification of a cost limit is optional; that is, the question may
not include the "below <unit-cost>" part. In response, the user may
find new vendors who offer these items, or check whether some known
vendors offer them. 

Alternatively, the user may notify the system that the lowest costs
for these items are already in the system. Then, the system adds the
known lowest costs for these items to the lowest-cost list, and the
elicitor does not ask the user to look for lower costs in the future.

For example, suppose that the system needs to order computers, and the
current cost table is as follows:

                        dell        hp      proj        vegie
  v1 ("First Vendor")   Indefinite  1500    Unknown     Absent 
  v2 ("Second Vendor")  Absent      Absent  Indefinite  600

The system may potentially order Dell notebooks ("dell") or HP
Notebooks ("hp"), but the only known option is HP Notebooks at $15 per
hour. If the system decides that it is too expensive, it generates
following question:

  Find vendors who offer Dell Notebooks or HP Notebooks
  with cost below $15 per hour

The user may then find a new vendor that provides computers, or she
may find out that First Vendor offers Dell Notebooks, which are less
expensive than HP notebooks.


CHECK WHETHER <VENDOR> OFFERS <ITEM-TYPE> OR ... OR <ITEM-TYPE>
AND FIND OUT THE RELATED COSTS

The system asks this question when it needs to satisfy some service
property, but it does not know whether a specific vendor offers
related items. If the user answers that the vendor offers them, but
does not include their costs, the system later asks about the costs.

For example, if the system needs to order Dell Projectors ("proj"), it
may generate the following question:

  Check whether Second Vendor offers Dell Projectors
  and find out the related costs


FIND OUT THE COST OF ORDERING <ITEM-TYPE> FROM <VENDOR>

The system asks this question when it knows that a vendor is offering
a specific item, but does not know the cost; for example:

  Find out the cost of ordering Dell Projectors from First Vendor