Advanced Perl Programming

Professors, Students, Courses

This example shows how you might represent professor, student, and course data as hierarchical records and how to link them up. Assume that the data files look like this:

            #file: professor.dat
id          : 42343                #Employee Id
Name        : E.F.Schumacher
Office Hours: Mon 3-4, Wed 8-9
Courses     : HS201, SS343         #Course taught
...


#file: student.dat
id          : 52003                 # Registration id
Name        : Garibaldi
Courses     : H301, H302, M201      # Courses taken
...
#file: courses.dat
id          : HS201
Description : Small is beautiful
Class Hours : Mon 2-4, Wed 9-10, Thu 4-5
...

Each “id:” line starts a new record.

Among other tasks, let us say we are required to find out whether there is a scheduling conflict on professors’ and students’ hours. Because our focus is on data representation and getting a feel for Perl’s reference syntax, we will look at implementing only some parts of the problem.

Representation

A hash table is a good representation for a heterogeneous record, as we mentioned earlier, so a student structure may be implemented like this:

$student{42343} = {
    'Name'    => 'E.F.Schumacher',
    'Courses' => [ ]};

A number of subtle design choices have been made here.

We could have replaced “foreign keys” (to use the database term) such as “HS201” with references to the corresponding course data structures. We didn’t, because it is then tempting to directly dereference these references, in which case the student code is aware of how the course data is structured.

We maintain separate global hash tables for ...