Chapter 12: Mediator Application Examples.
12.1 -- The terrain reasoning mediator accesses
an Ingres relational data base, a quadtree spatial data structure,
and CAMMS (Condensed Army Map Mobility System) data of an area near Lauterbach,
Germany through predicates (see Fig 12-1) to determine optimal paths between
target sites and facilities.
An interesting terrain query involves an unusual
supply item, a "secret_agent". Curious about this asset, we might query
such "supply" locations through the site_facility_supply predicate
as shown in Fig 12-2. The answer (see Fig 12-3) tells us that there
are eight secret agents at site_1, coordinates (102,103).
Now perhaps we need to plot a route to a secret
agent from, say coordinates (97,97). We can request this through
the query listed in Fig. 12-4; the results appear in Fig. 12-5..
The result in Fig. 12-5 tells us that our position
is 42 units from the agent with a projected path traversal cost
of 84.7 (actual path coordinates appear within the square brackets
-- the plot appears in Image 12-1).
In this case Hermes may not have rendered
the best solution as we requested the best route to first facility it found
with a secret agent listed in the supply. We may be able to do better by
prompting Hermes to check all facilities with secret agents attached and
return the one with the lowest route cost (see query in Fig 12-6, result
in Fig 12-7, plot in image 12-2). This new solution tells us that we are
30 units distant from an agent with a path traversal cost of only
Perhaps we have a task for the agent -- We need
him to go to a site where there is an F-14 fighter; We also want to know
the agent's distance from the F-14. The query listed in Fig 12-8 will give
us this information. The solution, listed in Fig 12-9, tells us that there
is an F-14 fighter at the same location as the secret agent, distance zero.
12.2 -- The robotic inventory mediator accesses
nine databases (Ingres, Hermes, and relational flat-file
storage types), three at remote locations accessible through the Internet,
to process the necessary spatial storage and supply requisition queries.
12.3 -- The banking mediator accesses over
fifty dispersed databases using Oracle (pending license
issues), Hermes, and relational flat-file stores, to simulate
a network banking system.