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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.


Trakla2 web environment menu

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).


TRAKLA2 applet

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)