Internet-based Training of Data Structures and Algorithms

Ari Korhonen, Lauri Malmi
Department of Computer Science
Helsinki University of Technology
Ari.Korhonen@hut.fi, Lauri.Malmi@hut.fi

Abstract

In this paper, a learning environment for the data structures and algorithms course is presented and discussed. The system is based on combining standard telematic tools like email, newsgroups and WWW pages with a dedicated tool for the target course, and the experience shows that such a combination is highly successful in a mass couirse of hundreds of students.

This paper is available in the URL: http://www.cs.hut.fi/~lma/TRAKLA_text.html.

1. Introduction

Helsinki University of Technology (HUT) is the leading technical university in Finland. About 1300 new students are enrolled each year, and of these over 200 start the computer science curriculum. In addition, most students from other curricula take several computer science courses during their studies. For example, the number of students which take the basic programming courses varies currently from 200 to 700 students per course.

Due to the vast masses of students on the basic courses we have used different telematic tools, like email, newsgroups and WWW for information delivery and communication over 10 years. In addition, several projects have been carried out for developing tools which aid studies, especially in the programming courses. One of such tools is the WWW-TRAKLA system, which we use for teaching data structures and algorithms /1,2/. It is a dedicated tool for the delivery and automatic checking of algorithmic assignments. This tool is an integral part of the course and it enables us to provide assignments for the students such that were not possible when using human teaching resources. We can use personally tailored non-trivial assignments, give immediate feedback for the students and allow them to correct their answers. As a result of using such possibilities we have very good learning results.

The TRAKLA system has been used in HUT since 1991. During the first years all communication with it and the students was carried out by email, and in 1997 the Web interface was added. Currently we are working in the LEAD project /3/ in which we develop a learning environment of data structures and algorithms.

In the current project we have discussed a lot the role of different telematic tools in education. Our experience shows that each of them can have its own role, which often partially overlaps the role of other tools. Moreover, we feel that standard tools like email, newsgroups and WWW pages are quite sufficient for building a good learning environment. This view is somewhat contradictory to the current trend where integrated learning environments, for example, the WebCT tool, are being developed. We argue that integrated environments have some problems which traditional tools do not have. First, the students have to learn a new system instead of using general-purpose tools which they use in their everyday communication. Second, some maintainance work have to be done by the teacher when a more obvious way would be to use system maintainance resources. Third, it is not so obvious how to add new facilities to these tools, when the existing properties fail to meet the needs of a particular course. This holds in our case, since we necessarily use the TRAKLA system for the registration of students. Moreover, TRAKLA uses the standard tools for communication and we find no advantages of using it in parallel with some integrated tool. Actually we have concluded that what we need in our courses is a simple way of configuring an environment for each course separately, such that uses the standard tools and allows a loose interface for adding dedicated tools to the environment.

In this paper, we consider first in the Section 2 the general needs for electronic communication in our courses. In Section 3 we discuss how various telematic tools respond to these needs. In Section 4, we present our experiences about the WWW-TRAKLA system and in the final section we discuss, how we see the field of electronic communication in education in general.

2. General communication needs

In the following, we discuss the needs for communication from the view of the basic programming courses since we have been developing their contents and organization for a long time. Most of the observations, however, are relevant for other basic courses, as well.

The basic courses in HUT include an introductory programming course (5 credits) followed by a course of data structures and algorithms (3 credits). The first course has 3 parallel versions, of which one is dedicated for students of computer science curriculum and the other two are directed to students from other engineering curricula. The second course has two parallel versions.

We have identified the following needs in communication between the students and the teachers.

The teacher needs facilities for delivering information for the students. This information includes, for example, the schedule and requirements of the course, supplementary course material, announcements etc.
Students need advice during their studies and they need to discuss with their fellow students. The advice and discussion can be either private or public.
The teacher needs to collect feedback from the students. It is good to have a possibility to give anonymous feedback since some students may worry about their grades if they critisize the course contents or arrangements on their own name.
The teacher sets up assignments for the students and they return their solutions, essays etc. for evaluation. The evaluation can be either manual or automatic.
The students need enough feedback about their work.
The teacher may want to allow students to read the work of other students, for example, in order to provide examples of good work or to allow the students to critisize the work of other students.

In addition, we have to live with some practical limitations. First, the human teaching resourses are very limited. For the denoted five courses we have in total 4 full-time teachers and several tens of student assistants. The teachers typically give the lectures, provide course material and organize the arrangements of the course, and the student assistants give guidance in the classroom exercises and during the office hours. Second, many students do not attend the lectures, either because they have other lectures at the same time, or because they want to study on their own. A number of students are working full time and therefore they take the course as distance education. Thus, we have a very different environment compared with traditional classroom courses.

3. Technical solutions for general needs

Various electronic communication tools are very useful for meeting the challenge described in the previous section. Since there is nothing new in this, we present only briefly the role of email, newsgroups and WWW in our courses. We also stress here that although we discuss only the electronic communication, we have no aims of transferring whole courses into the Web. We have lectures, classroom exercises, and office hours for discussing problems personally with the students. The electronic communication only supplements these traditional teaching methods.

3.1 Email

We use email especially for personal communication and advising.

Each course has a unique email address to which the students can send their questions. The student assistants read this email and answer the questions during the course. The students get the answer typically within a few hours, or at the latest on the following day (exluding weekends). Since the number of messages is large, the teacher does not respond to these messages.
The student assistants direct some questions and comments to the teacher, if they feel they cannot answer them. Some students also send messages directly to the teacher, but we do not encourage this in practical programming problems. The teacher has no capacity for handling many such problems.
When the students are working on their personal project, each of them is assigned a particular student assistant who guides their work, accepts the demonstration of the project and assesses the code and the documentation. Then, the student is given the personal email address of the assistant and they can communicate directly with each other without the extra delay caused by the course mail address, which is monitored by other assistants.
Since we have a register of the email addresses of all students, we occasionally send a message to all of them. Such messages deliver urgent information, which should reach the students fast.
In addition to weekly meetings with the student assistants the teacher gives guidance to them by email, too.

3.2 Newsgroups

Newsgroups are used for delivering annoucements and as an open discussion forum.

Each course has one or two newsgroups. In the latter case, one newsgroup is used for announcements given by the staff, and the other is used for questions of the students and for discussion. The separation into two groups has been useful since then it is easier to find the appropriate announcement messages afterwords. The discussion group is, of course, followed by the teacher and the student assistants. Occasionally also some other faculty members give answers and typically technical comments to the questions, although they do not belong to the course staff.
When the teacher wants to give answers to email questions which are of general interest to students, he sends them to the discussion newsgroup in addition to the student who made the initial question.

3.3 WWW

World Wide Web is used for delivering information and collecting feedback.

Each course has a home page which contains long-term information about the course, such as contact information, course description and schedule, guides for exercises and projects etc. Some information is delivered both in the newsgroup and on the WWW page, but typically long and complicated instructions are better presented in the Web.
Web is a natural tool for publishing supplementary material for the course.
The results of the assignments and projects are published in the Web. However, we restrict this information so that it can be accessed from computers under the university domain only. We do not wish such pages to find their way into search engines like Alta Vista, e.g.
The students can send feedback from the WWW page to the teacher. During the course there is a simple feedback form using which feedback can be given anonymously. The teacher reads the feedback and responds to it in an appropriate way. Often the response is published in the course newsgroup together with the initial feedback text.
At the end of the course, or at the end of some of the course, a feedback questionnairy is published in the Web. A simple script program is used for gathering the statistics about the answers.

4. The WWW-TRAKLA system

In short, TRAKLA is a system which delivers assignments for the students, receives their answers and grades the answers automatcally. The assignment are non-trivial in the sense that the students have to simulate the working of different algorithms and show how the given algorithms change the contents of data structures they handle. An example: "Insert the following keys in this order into an empty binary search tree, E X A M P L E T R E E. Show the final tree. Thereafter delete the keys R and X and show the final tree."

In the email-based TRAKLA system the students send their answers by email in a predefined format to the TRAKLA server. This arrangement has some obvious drawbacks. First, the students may loose points for trivial format errors which have nothing to do with the initial assignment. Second, most data structures are more naturally presented in a graphical form instead of some cumbersome Ascii presentation format. In order to remove these problems, the WWW interface to TRAKLA was built in 1997 / 2/. It gives each assignment a graphical editor which presents the data structures in their natural form. The students can solve the problem by using the keyboard and the mouse in the interaction. Moreover, they can browse their solution backwords and forwards as a list of states of the data structure. Thus, they can ensure that their solution is correct before submitting it to evaluation. WWW-TRAKLA then converts the answer to the format understood by the TRAKLA server and sends the answer to it.

A very important feature of the system is that we can generate a unique initial data for each student. Thus, although the basic assignment is the same for all students, they all have to solve a personally tailored assignment. This has obvious advantages for learning. They cannot copy their answers from anybody. Moreover, we can now encourage natural co-operation between the students. They can discuss the problem freely so far they do not solve each other's assignment totally.

A second, very important feature is that the system gives almost immediate feedback for the students after the submission. They get the grading and we allow them to correct their answers a few times, typically 3-5 times per assignment. This allows them to learn from their mistakes. We stress here that they have to think about their solution anew for each new submission, since the solution space of the assignments is simply far too large for using mechanical trial-and-error method.

After the deadline for submitting the answers we send the model solutions for all students by email. Thus, they can check what was wrong, if they did not get everything correct.

For most assignments we provide hints in the Web. We have also an exercise mode of the assignments. This feature means that the students can make free exercises on a given fixed data, submit their answer and get the model solution for that data. They can thus exercise on the topic before working with their own personally tailored data.

5. Experiences and further development

We have tried to find ways how various telematic tools could support best the learning process on our courses. In many cases we have been successful, since the students give good feedback to us and the learning results are good. In summary, our experiences about the standard tools are the following:

The email service works well in a mass course, when there are enough assistants for answering the questions so that we can guarantee fairly quick response to questions and comments. This suits well to many students, who work at home and dislike coming to the campus at certain a time. The student assistents also like to work at home in the evenings.
It is important to identify the responsibility strictly for each assistant. We have used both temporal sharing of responsibility, e.g., an assistant takes care of email service one week at a time, and responsibilities related to certain topics or student groups in the course.
The email service works only on small problems and on routine matters. In complicated programming problems face-to-face discussion is preferred.
The teacher should limit his/her part in email advising, since it is more difficult for him/her to guarantee quick response time.
The newsgroup discussion is a useful tool both for the students and for the staff. The students send questions to the newsgroup and they often get the answer faster than from the email service, since the more advanced students willingly share their knowledge. Occasionally comments to some special topics are received from outside the course, when other members of the faculty follow the newsgroup, as well.
A newsgroup suits well for getting immediate feedback from the students as well as providing the teacher's comments for them.
WWW offers a nice way of organizing anonymous feedback from the students.
WWW is a wonderful tool for making questionnairies. If the students get some small advantage of answering the questions, very high percentage of them answers sincerely. The summary results are easy to publish in the web and the teacher can comment on them in the newsgroup.

TRAKLA has been a valuable aid for us. In spring 98, more than 500 students took the course of data structures and algorithms, and each of them had to do some 25 algorithmic exercises using the system. These exercises covered most of the basic data structures and algorithms discussed in the course. The results were fine. About 60 percent of the students received the highest grade of this part of the course, which required that they got at least 90 percent of maximum points. At this phase we do not have the final results about the course of this spring but the intermediate results seem to reach the same figures.

These results have given us as teachers a solid knowledge that the students truly have learned the basic topics in the course and we could set up more advanced exercises on this. Last year the other exercises dealt with inventing new algorithms for small new problems and analyzing the working of simple algorithms. This spring (1999) we gave them two larger design projects which they solved in groups of 2-3 persons. In the first project they devised basic algorithms and data structures for a simple search engine for documents. In the second project they invented algorithms for a system with which a person can query time tables and routes for public transport. An example, "give the fastest connections from point A to point B and which bus lines should be used".

The students returned their designs as HTML pages which we copied to our computer. Then, we sent the same designs, i.e., the URL, after anonymization, for evaluation for other groups. Each design was evaluated by five other groups and each group had to evaluate five designs, choose the best of them and write down their comments. The comments were returned as HTML pages and delivered to the original group, as well to us. In this way the students got a realistic view, how difficult it is to present a solution in a readable form and what kind of problems are encountered in the evaluation. Since each work was evaluated by a number of groups, we could compare their evaluation reports in addition to the original work. Both parts, the design and the evaluation was graded.

Our experience was that the students learned a lot during the design process and the evaluation. However, two such projects caused too much work for them. In addition, many students found the evaluation phase very difficult. Therefore the evaluation reports were partly superficial and contained obvious errors. We concluded that we cannot use the students for grading each other's work. The teacher and the assistants have to take care of it. However, the students should read each other's work and comment them.

The implementation of this phase was carried out by simple script programs, since we did not have a tool for managing such operations.

5.1 Some comments on a learning environment

The whole system we are using, which includes WWW-TRAKLA together with email, newsgroups and WWW pages can be considered a learning environment for data structures and algorithms. It works fine and supports most of our needs. We are, however, developing it further in the LEAD project /3/. Essentially, we want to enhance the feedback TRAKLA gives for the students. Currently it evaluates only a few intermediate states of the data structure, and it does not evaluate the process how the data structure entered this state. We shall add such a feature to the system, and then we shall be able to give better feedback, where the error occurred in the solution. Then it is also easier to prepare simple commented animation examples of algorithms as supplementary material. With such tools we aim to build more electronic course material in the Web. We are not going to include very much text in the new material, since a text book is a better tool for such representation. On the other hand, interactive exercises with feedback and commented example animations give some true extra value for using the environment.

During the development of our system we have had to consider, what is the role of each telematic tool that we use. We could summarize our view in the following way.

First, before taking any actions of using electric tools, define what is your problem. Do you need anything new or is current the traditional environment good enough for your needs? In our case the key problem was the number of students and how to provide enough feedback for them and to enhance the communication between them and us teachers.
Second, if there is an obvious problem, use the basic technology for your needs. The students know how to use email, newsgroups and WWW and they like to choose their client (mail program, WWW browser, etc. ) to such system. We should not push them using new systems. In our case standard email, newsgroups and WWW solved most of our problems.
Third, when standard tools are not suitable, try to find a working solution done by someone else. You probably will find it in the Web. In our case, no such tools were available when we started the TRAKLA project in 1990.
Finally, build your own system if no other solutions exist. Prepare to spend time and resources for implementation, maintainance and operation, and evaluate beforehand whether this pays for the advantages your claim to achieve.

We do not see that any integrated learning environment currently available could solve our problems, since the key problem is the dedicated feedback for a special course.

References

/1/ J. Hyvönen, L.Malmi, TRAKLA - A System for Teaching Algorithms Using Email and a Graphical
Editor. Proceedings of HYPERMEDIA in Vaasa'93, pp. 141-147, 1993.

/2/ A. Korhonen, World Wide Web (WWW) tietorakenteiden ja algoritmien tietokoneavusteisessa
opetuksessa (World Wide Web in Computer Aided Instruction of Data Structures and Algorithms), Master's Thesis, Department of Computer Science, Helsinki University of Technology, 1997.

/3/ The LEAD project home page. See, http://www.cs.hut.fi/~tred/LEAD/