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ANDES is designed to support students, teach<strong>in</strong>g assistants, and course adm<strong>in</strong>istrators. The roles of the clients<br />

and servers <strong>in</strong> the ANDES architecture are rather different from those <strong>in</strong> typical client-server architectures.<br />

Each student station is able to operate autonomously; when students are work<strong>in</strong>g through the course materials<br />

on their own, and are not <strong>in</strong>teract<strong>in</strong>g with <strong>in</strong>structors or other students, no connection to the central servers is<br />

required. Connection is established only at the beg<strong>in</strong>n<strong>in</strong>g and end of each session, and dur<strong>in</strong>g live class<br />

<strong>in</strong>teractions.<br />

3.1 The Student M<strong>in</strong>i-Server<br />

Autonomy is accomplished by <strong>in</strong>stall<strong>in</strong>g a Web server and CGI program locally on each ANDES student work<br />

station. This student m<strong>in</strong>i-server, presents course materials to the student as requested, and tracks the<br />

student’s progress through the course. The m<strong>in</strong>i-server presents the course materials us<strong>in</strong>g a conventional<br />

Web browser, namely Netscape. The student m<strong>in</strong>i-server contacts the central server automatically when<br />

needed, <strong>in</strong> order to obta<strong>in</strong> updates for course materials and report on student progress. The m<strong>in</strong>i-server<br />

approach provides a number of advantages over the conventional Web as a courseware delivery platform.<br />

Stor<strong>in</strong>g the course materials locally on the student mach<strong>in</strong>e greatly improves system response, and largely<br />

elim<strong>in</strong>ates download time dur<strong>in</strong>g courseware delivery. Autonomous courseware delivery reduces the amount of<br />

Internet connect time required, and thus reduces the connect charges to Internet service providers. Because the<br />

m<strong>in</strong>i-server resides on the student’s mach<strong>in</strong>e, it can do a better job of track<strong>in</strong>g student activities and<br />

controll<strong>in</strong>g the user <strong>in</strong>terface than a server resid<strong>in</strong>g on a remote mach<strong>in</strong>e can. Because the m<strong>in</strong>i-server prefetches<br />

all lesson materials at once, it does a better job of improv<strong>in</strong>g system response than general-purpose<br />

mechanisms such as cach<strong>in</strong>g.<br />

ANDES refers to all assets by handles, or aliases that are resolved at runtime to yield an absolute path and file<br />

name. Handles enable courseware developers to replace or supplement assets over the life of a course. A<br />

global dictionary is used to store the actual pathnames. This approach allows courseware to be updated at any<br />

time, by download<strong>in</strong>g the updates from the central server and updat<strong>in</strong>g the handle dictionary. It also permits<br />

performance tun<strong>in</strong>g of the courseware, e.g., copy<strong>in</strong>g CD-ROM assets temporarily to hard disk.<br />

3.2 Student Workstation Organization<br />

Fig. 2 shows the architecture of the student workstation. It <strong>in</strong>cludes a Web browser (Netscape), a Web server<br />

(MacHTTP or WINhttpd), and several additional processes for retriev<strong>in</strong>g, display<strong>in</strong>g, and manag<strong>in</strong>g<br />

courseware.<br />

Figure 2: Student workstation architecture.<br />

The Netscape browser communicates with a number of helper applications <strong>in</strong> order to present courseware to<br />

the student. A customized application is used to startup workshops that have been authored <strong>in</strong> Macromedia<br />

Director. The m<strong>in</strong>i-server currently runs these workshops as separate, full-screen external applications because<br />

the Netscape plug-<strong>in</strong> for Director movies, Shockwave, does not yet support local file I/O. Other helper

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