Hello List,
I have a problem with a query that I have written. For an Automatic
Course Scheduling System, I have created a query that checks each fact
in the working memory (which is a shadow fact of a Java-Course-object)
for the instructor name. Unfortunately, something goes wrong, but I
don't know what. Another query that finds all courses starting at the
same time works, though.
Let me show you an example. I am running the following code in a
main-method in a random class:
First, I create an Rete-object, an array that stores my query-results
and a vector of courses.
try {
Rete r = new Rete();
QueryResult[] results = new QueryResult[2];
Vector<Course> courseVector = new Vector<Course>();
I fill the vector with plain old java Course-objects. The first field in
each course is an course-ID (int), the second is the start time (int)
and the last one is the Instructor (String). Nothing else is in the
class (besides the get-methods for the above fields).
courseVector.addElement(new Course(1, 800, "Hawkins"));
courseVector.addElement(new Course(2, 800, "Einstein"));
courseVector.addElement(new Course(3, 1000, "Hawkins"));
Then, I define the Course-class in Jess and add the Course-objects as
shadow-facts to the working memory.
r.defclass("Course", "AutomaticScheduler.engine.Course", null);
for (int i = 0; i < courseVector.size(); i++) {
r.definstance("Course", courseVector.elementAt(i), false);
}
After that, I define the queries... one for the
start-time-collision-detection and one to show every course by the same
instructor.
r.eval("(defquery detect-starttime-collision (declare (variables
?var)) (Course (time_start ?var) (CRN ?crn)))");
r.eval("(defquery find-instructor (declare (variables ?var))
(Course (instructor ?var) (CRN ?crn)))");
I run the queries and store the results in the array.
results[0] = r.runQueryStar("detect-starttime-collision", new
ValueVector().add(800));
results[1] = r.runQueryStar("find-instructor", new
ValueVector().add("Hawkins"));
Last, but not least, for every position in the array, I print out the
position number and the outcome of the result. At the end, it is
necessary to catch some exceptions, of course.
for (int i = 0; i < results.length; i++) {
System.out.println("results[" + i + "]:");
while (results[i].next()) {
System.out.println(results[i].getString("crn") + " " +
results[i].getString("var"));
}
}
}
catch (JessException je) {
je.printStackTrace();
}
}
So far so good. When I execute the code, the following lines are output
to the console:
results[0]:
1 800
2 800
results[1]:
That's it! The two courses with "Hawkins" as the instructor do not come
up! Although the result[] at position 1 is NOT null, it seems to be
empty; i.e. no course with that instructor name can be found. This is
still the case, if I do not query for the start time and/or when I FIRST
query for the instructor, THEN for the start time.
Actually, I expected the following as the output:
results[0]:
1 800
2 800
results[1]:
1 "Hawkins"
3 "Hawkins"
What is wrong? I believe it has got something to do with the fact that I
am query-ing for a String instead of an int (because the two queries are
basically the same). I really appreciate any help I can get because at
this point I seem not to be able to see the forest due to all the trees ;-)
Thank you very much in advance for your help!
Bastian
