Contents
General
TRAKLA2 is a Web-based, computer-aided learning environment for
helping to teach algorithms and data strutures. Not only does TRAKLA2
provide links to visualizations that portray a variety of algorithms,
but it also distributes tracing exercises to the student and then
automatically evaluates the student's answers. The student enters his
or her answer to these exercises using an interactive graphical editor
that is coded in the Java language. Thus, a Java enabled web browser
is needed in order to solve the exercises.
The student manipulates conceptual views of data structures
simulating actions a real algorithm would perform. The exercises are
individually tailored for each student. Actually, the system provides
a new input each time the student tries to solve an exercise. This, in
turn, allows the student to practise the algorithm until it is
learned. Progress on the course can be followed in real time at the
exercise page that shows the points received from each exercise. The
following features are supported in the current version:
- All manipulation is carried out in terms of graphical user
interface operations.
- The system records the sequence of actions prepared by the student
that can also be browsed backward and forward.
- The student can request the grading of the solution at any time.
However, after each grading action, the student cannot continue
solving the exercise with the same data. Instead, the exercise must be
re-initialized with new random data.
- In grading, the server compares the user sequence of data
structure states to the sequence generated by the real algorithm.
- The initial data for an exercise is personally tailored for each
student.
- The initial data for an exercise is tailored anew each
time the exercise is solved.
- The student can always request the model solution for
the personally tailored exercise. The solution is presented as an
algorithm animation that the student can browse backwards and forwards
freely. However, as with grading, the student has to reset the
exercise and start with fresh random initial data before he/she can
resubmit the solution.
- The systems logs some information about the user interface actions
for statistical analysis. This data aids us in improving the system
itself, tuning individual exercises, and understanding students'
learning better.
The Web Environment
The TRAKLA2 system is used through a dynamic web environment. In
order to use the environment, each student needs a username and a
password. In different Universities, the TRAKLA2 usernames are
managed differently. At the Helsinki University of Technology, for
example, the student's student number is used as username. Ask your
teachers what kind of usernames are used in your institution.
Most of the functionality in the web environment is contained at the
server in order to make the system work on as many web browsers as
possible. The system consists of three different pages: the
main page where you can see an overview of a course,
exercise page where you can solve exercises, and
settings page where you can manage your personal
settings.
The main page is reached after login. On this page, you can
see an overview of a course and your current results. From this
page you can select an exercise for solving, or change the selected
course, if you are on multiple courses.
The exercises can be selected from a list (shown in figure 1). For
each exercise round the list shows if the deadline for the exercise has
passed, has the exercise been submitted, points given for the
exercise, and the point maximum. Also, if the number of allowed
submissions is restricted, the number of submissions is also shown. In
figure 1 the number of submissions of the exercises on the second
round is restricted to five submissions each.
In figure 1, the deadline for the first exercise round has
passed (indicated with the red deadline time), and
the deadline for the second round has not passed.
The exercises where the background of the points and submissions columns
is green (i.e. the third exercise of the fourth round) have been
submitted with full points. Exercises where the background is yellow
have been submitted without gaining full points, and exercises
where the background is gray or white have not been submitted.
If an unfinished exercise has only one submission or no submissions left, it is shown on a red bacground.
Figure 1
The main page of the TRAKLA2 web environment. The figure shows
the student's name, course code and two exercise rounds on the course.
The exercises are solved using a Java applet that is tailored to
each exercise separately. The applet includes visualizations of data
structures needed in the exercise, push buttons for requesting Reset,
Grade and Model solution for the exercise, as well as buttons for
browsing one's own solution backwards and forwards. Simulation is
carried by dragging and dropping data items or references from one
position to another. Some exercises also include additional push
buttons to perform specific operations such as rotations in trees.
The Applet
The Java applet allows students to solve
exercises by directly manipulating the data structures represented
graphically. As a matter of fact, the user manipulates an actual
data structure through the GUI. We call this Algorithm
Simulation. This has several benefits. First, the exercises can
be assessed automatically in order to provide instant
feedback. Second, we can provide individually tailored exercises
that one can apply to test his or her understanding of a particular
data structure or algorithm. Third, if the student fails to solve an
exercise, the system is able to provide model solution for each
problem instance.
Interaction
The GUI for each exercise has the same look and feel. However,
some exercises might require special purpose buttons and functionality
that are explained in the assignment. In general, however, the GUI
is composed of the following parts.
Control panel and buttons appear on the top of the screen. These
are common for all exercises. One can adjust the font size, apply
the control panel called Animator or push the control buttons
that are used for resetting the exercise, viewing the model answer,
and for grading and submitting the answer to the server. Below the
control panel appear the data structures the student is asked to
interact with. Usually, the upper structure is the input data
structure for the algorithm in question. The user manipulates the
lower target data structure, for example, by drag and dropping the
input keys - or any object - into the target structure.
An object (key, node, reference, or the whole structure) can be
selected by using the left mouse button. The very basic manipulation
process includes only drag-and-dropping these objects. In order to,
for instance, insert a key from an array into a binary search tree,
the selected key must be drag-and-dropped from the array to the
tree. If an exercise contains tasks that are not possible to
complete by just drag-and-drop, special command buttons are provided
(See Figure 2).

Figure 2. A Typical Trakla2 Applet. Animator, Commands
and Font size -selector are always present.
Animator
With the Animator control panel one can
traverse through the animation sequence backward and forward and
look at the changes performed during the simulation process. The
simulation can be continued at any point (of course, the states in
the sequence appearing after the new operation are lost).
- Backward - go to the previous state, if that exists.
- Forward - go to the next state, if that exists.
- Begin - go to the first state.
- End - go to the last state.
Control Buttons
- Reset - initialize the exercise. This also resets the input
data (new random items). In some exercises the Reset button is not
enabled until the exercise has been submitted.
- Model answer - create the model answer.
The model answer opens into a new window so that it is viewable side by side
with one's own solution. Note, however, that it is not possible to submit an exercise
after the model answer is revealed without resetting the
exercise first. In some exercises the Model answer button is not enabled until the
exercise has been submitted.
- Submit - compare the answer with the model
solution and submit answer to the server. The system informs how many steps are
correct out of all steps in the animation sequence resulted from
the algorithm simulation.
- Font size - this selector allows to change the size of the
visualized data structures. Note, however, that the applet area
must be predefined and thus too large selection might result some
of the structures to disappear from the screen.
System requirements
A Java2-compatible browser is required to run Trakla2. Trakla2
uses ports 1089 and 1099 for communication between client and
server. If these ports are blocked by a local firewall, Trakla2 may
not work properly. Cookies must also be allowed for this site to use
the system.
We have tested the system on several different platforms,
and have noticed some problems. Here is a list of compatible
platforms where Trakla2 has been tested:
- Windows 2000/XP
- MacOS X
- Camino, Firefox, Seamonkey (Mozilla)
- Safari
- Opera 9
- Linux
- Netscape 7, Mozilla 1.x or Firefox 1.x
- Opera 9
We recommend using Java version 1.4.2 or newer.
Incompatible platforms:
- MacOS 8.x - 9.x (any browser)
- Mozilla Firefox 0.x (Windows, Linux)
- Netscape 4.x (Windows, Unix/Linux, MacOS)
- Microsoft Internet Explorer for Mac (MacOS)