abstract
in this paper, we describe the design of the webvl system, a web-based virtual programming lab for on-line distance learning. the underlying setting is a collection of computers hosting education and programming software. students use personal computers at home to access over the internet one of the lab servers, which is typically located at a school. the lab server performs functions to accommodate the various requests from the student, ranging from downloading software from the school lab servers, working through interactive demonstration and tutorial sessions, and submitting a program for execution on a lab computer using specified software package.
the collection of computers forms a virtual programming laboratory because the machines can be located in different buildings and even at different campuses. it facilitates resource sharing among different schools and overcomes the limit of geographical distances. the webvl system design includes an agent-based client side functions and interface, the structuring of lab servers, the mechanisms to locate user requested software packages / services and to present various forms of data and information, and the interfaces to various education and programming software packages. technologies such as virtual reality, java applets and servlets, mobile agent, xml, and web/http servers are used to implement the underlying mechanisms and facilities of the virtual lab, such as software resource locating and interfacing, real-time interaction, and information presentation. using these technologies allows the system to achieve high-performance, scalability, and disconnected operation through reduction in network bandwidth and delay, load balancing, and code mobility.
1. introduction
during the last several years, e-learning has emerged as one of the fastest-moving trends in education and is booming. thanks to the widespread access to the internet, on-line education is enabling students and professionals to learn from afar, keeping pace with technological and managerial changes. thousands of technical and management courses are now being offered by universities, for-profit professional development centers, and industry training facilities worldwide [ube00].
underpinning the teaching and learning over the web, the global connectivity of the internet and a new generation of hardware and software applications have equipped distance learning with new methods of delivery. the convenience of web education made distance learning effective and flexible, even in the absence of face-to-face interactions in the classroom. nowadays, students who take courses on-line can access the courses whenever and wherever convenient. they can download the lecture note from the web, communicate with each other and their instructor through e-mail, and took exams by responding to questions on computer screens.
although several e-learning software supporting on-line lecturing and tutoring have been found popular [web, wbt, lea] and many works have been done in providing web-based learning and teaching [ibr94, swi97, shi00, ube00], there has been not many reports on providing students convenient on-line access to programming facilities available in computer labs. a few work can be found which develops either ad hoc or special purpose web programming facilities [sha97, mci98, row99]. in this paper, we describe the design of the webvl system, a generic web-based virtual programming lab for on-line distance learning. the powerful features of the www, especially the integration of most widespread internet protocols, allow us to design software to facilitate the access to almost existing resources available on the internet in an integrated fashion [ibr94]. in addition to navigation through hypermedia documents, using the remote access capability of the internet technology, various software programs can be executed remotely through www. in our design, the underlying setting is a collection of computers hosting education and programming software. students use personal computers at home to access over the internet one of the lab servers, which is typically located at a school. the lab server performs functions to accommodate the various requests from the student, ranging from downloading software from the school lab servers, working through interactive demonstration and tutorial sessions, and submitting a program for execution on a lab computer using specified software package.
the collection of computers forms a virtual programming laboratory because the machines can be located in different buildings and even at different campuses. it facilitates resource sharing among different schools and overcomes the limit of geographical distances. the webvl system design includes an agent-based client side functions and interface, the structuring of lab servers, the mechanisms to locate user requested software packages / services and to present various forms of data and information, and the interfaces to various education and programming software packages. technologies such as virtual reality, java applets and servlets, mobile agent, xml, and web/http servers are used to implement the underlying mechanisms and facilities of the virtual lab, such as software resource locating and interfacing, real-time interaction, and information presentation. using these technologies allows the system to achieve high-performance, scalability, and disconnected operation through reduction in network bandwidth and delay, load balancing, and code mobility.
the rest of this paper is organized as follows. section 2 describes the requirements of the webvl system design. section 3 presents the overall system architecture and describes the functional components of the system. section 4 discusses implementation issues. finally, section 5 concludes the paper and describes our future work.
2. system requirements
we have carefully studied the requirements of student programmingexercises in developing the on-line virtual laboratory services. the virtual laboratory system to be developed should support students located in different geographical areas, who need on-line and real-time access to programming facilities from a number of different sources. students have choices of submitting a program for compilation and execution, obtaining the results, conducting (possibly interactive) testing/debugging runs of programs, reading help files and software manuals, etc. our main objective of this research is to prove a general framework for web-based access to programming lab facilities.
reflecting these requirements, our design of the webvl system aims at architecture with the following features::
· accessibility: the service of provided by the system must be widely accessible. we decided that the service should be provided on the internet, using www to reach to a wide range of students. students can access webvl on campus in the physical laboratory, and from their home through dial-up connection using ppp or slip, using various platforms. web browsers also create user friendly environment.
· easy to use and effectiveness: the system should provide a user-friendly interface to facilitate ease use of the virtual lab services and should confirm to real-world programming practice. the user interface allows the user to select the desirable services in an integrated manner. it should provide an introduction to the virtual lab system, a comprehensive window-based menu of services, and other relevant information about the virtual lab.
· interactivity: interactivity is important when students doing programming exercises using a software. the system should allow the user to conduct interactive sessions with interaction-enabled software.
· multimedia: the system should provide multimedia information to the user to enhance their comprehension of the information provided. in addition to text description, the system should provide video and audio clips for viewing properties information.
· efficiency: the system should efficiently locate the software requested by the student, providing resource sharing with location transparency and workload balancing.
· modularity and extendibility: the system should be designed with modules that interact with each other only through their interfaces so that they can be replaced without affecting other parts of the system. new components and modules can be added and/or new requirements can be satisfied. this also increases the flexibility of the system and its capability of keeping pace with the new features rapidly occurring in the e-learning world.
to achieve the above goals, the structure of the system must be well designed. in the next section, we present the design of the system architecture.
figure 1: system architecture of webvl
3. system architecture
the webvl system has a web-based client-server architecture and consists of three major functional modules:between the client computer and the remote platform on which the requested software runs. it formats the student's input data for transmission to the remote server and converts the message data received from the server into the format suitable for display at the student's terminal.
figure 3: the structure of csa
3.3 server-side agent (ssa)
the ssa is responsible of carrying out the request from the distant student for programming using specified software at the server site. it interfaces the software for executing commands, invoking functions, and passing data. it also needs to interact with the csa. figure 4 shows the structure of the ssa.
figure 4: the structure of ssa
software used in a lab can be classified according to the platform on which they are executed and their interfaces: interactive vs. batch processing, gui-based vs. command line interpreter based, etc. one important task of ssa is to provide a mapping of the interface of the software to that to be displayed at the student's computer. the simplest case is when the software has a command line interface with possibly some parameters. in this case, a "direct mapping" can be easily performed. things can get much more complicated if the software has its own graphical user interface and its execution requires interaction with the user. in this case, conversion and wrapping up are necessary. providing a standard interface to software permits flexible linkage of the software into the particular programming course design adopted by individual teacher.
3.4 c-s transport protocol (cstp)
once the csa finds the target server site for carrying out the student's programming exercise, it will set up a connection to the ssa at that site. in principle, the interaction between the student and the software is in the form of input from the student and the response from the software. since the interaction can be of various forms, the cstp is needed to provide a communication environment necessary to facilitate the interactions. the csa and ssa communicate using the c-s transport protocol which provides a message passing facility that permits data and commands to be encoded and transmitted within web browsers and accessed by csa and ssa. the cstp should have the property that all data saved as the cstp specific format should be able to be accessed by csa and ssa who know how to recreate the data from this. this will facilitate the mapping of the lab software's interface objects at the student's computer.
4. implementation considerations
in this section, we discuss the issues and considerations in the implementation of the proposed webvl system using current technologies, which provide cross-platform and worldwide accessibility, support for "interactive" documents, ease of integration of multimedia/hypertext materials, and sophisticated network and database connection protocols [dei00].
figure 5 shows the physical system implementation model, where students as clients connect to the webvl system structured as a group of lab servers. each lab server maintains a collection of lab software. some of the lab software can be partially or fully replicated at the lab servers.
figure 5: implementation model of webvl
in the implementation of the gui, major functions of the web pages can be implemented using various tools, including web authoring tools, java applets, scripting (e.g., javascript), screen-capture software, and vrml. the rooms metaphor, a concept introduced by xeroxparc [car91, swi97], can be used to mimic the real-world laboratory environment in terms of interacting with the computer and organizing the lab documents. for example, with the use of internet-oriented virtual reality technology [har96, vrml], the gui can be designed to provide a illusion that the students enter a lab room to sit in front of a computer to run a program and, at the same time, gain access to different information resources located in the room. dynamic web pages with increased interaction with the user and sophisticated visual effects can be achieved through the use of javascript, dhtml and applets. other aspects of the gui implementation such as two-way dialog with the server (interactivity between the student and the lab software) through the gui will be discussed in the following sections.
