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Tim Anderson
13 May 2011

The Prolog engine that we use, as instantiated by Galileo, includes an
add-on library that defines a new amil_query predicate. This allows
Prolog to *read* values from AMIL, and use them in its computations;
as discussed in amil-programming.txt, AMIL may run executables or
invoke web services (Pro/E) to obtain those values.

There are 2-, 3-, and 4-argument versions of the predicate. The first
argument is take to be a variable; on successful execution of the
query, the list of returned values will be unified with that
variable. The second argument is the query; the third, if supplied, is
an attribute name (defaulting to "value"); the fourth, is supplied,
says whether to return all values found, or only the first. The
default is to return all.

The query itself consists of one or more terms. If there's more than
one, the whole thing must be a list. The first (or only) term should
refer to a node, by name. If all we care about is the name, then it
can stand by itself:
amil_query(X, 'LowFidelityRampMass')
will get the value attribute of the named node.
The most general form of the single-term query is:
node(NODE-NAME, attribute(ATTR-NAME, ATTR-VALUE),...,parameter(PARAM-NAME, PARAM-VALUE)...)
The attribute and parameter terms can appear in any order. The
attribute terms constrain the search (these are most useful on links;
for a node, since the unique name must currently be supplied, they can
only cause failure): whatever is returned must have attributes with
the supplied names whose values match.
The parameter terms are passed to AMIL as part of the query,
overriding whatever values are associated with the specified node in
the database.

If there are multiple terms, they should alternate
node/link/node/link. For a link, the format is the same, except the
name refers to the link's *type* rather than to its "name." Only
outbound links are searched. Thus:
amil_query(X, ['LowFidelityRampMass', 'parameter'], name)
will (or at least should) return a list containing the names of all
parameter links outbound from the LowFidelityRampMass node.
amil_query(X, node('LowFidelityRampMass', parameter('ArmorThickness',Thickness)), value)
returns the mass, as computed based on the specified thickness rather
than whatever various models might come up with.