AXLE builds upon the view of document delivery promulgated by projects like Apache's Cocoon. In these projects, the view of a typical web server as a system for delivering static HTML files with occasional calls to dynamically create an entire HTML page "from scratch" is replaced by view in which documents are routinely delivered by passing XML-encoded content through a pipeline of transformations that eventually result in an HTML, PDF, or other web-viewable content form.
AXLE builds upon that
view by proposing a standard document pipeline for delivering most
course content. Typical course content is presumed to follow a model
as shown here. The content is obtained as an XML (or HTML) document,
called the reference document. This is then transformed into a
browser-readable form (usually HTML) by a rendering
transformation that adds no new content to the document, but reformats
it into a form acceptable for delivery to the student's web browser.
If the reference document is already HTML, it's possible that the rendering transform is a trivial (identity) transform that actually does nothing. On the other hand, some rendering transforms might be quite elaborate. It is also possible that some reference documents are themselves produced by a series of document transformations. However, the reference document is defined to be the earliest form in which all meaningful content is present.
AXLE augments this
basic pipeline model by adding two additional transformations:
- Xlinks contained in a separate xlink-base are resolved against the reference document to add additional hypertext links and other structures not present in the original reference document.
- Conditions encoded in XPaths are checked against student information records to selectively include or exclude portions of the transformed refrence document.
The augmented AXLE pipeline offers two important capabilities to the delivery of course documents:
- Dynamic annotation: As entries are added to the xlink base,
delivered documents appear to acquire new links and/or added
content. Some uses of this capability:
- Instructors may provide web content from outside the course, but attach their own commentary or questions.
- Instead of directing students to use a separate bulletin board or discussion forum area for posting questions or conducting discussions and hoping that students will notice when relevant postings have occurred, links to the the discussion threads can appear in course documents directly alongside the paragraphs being discussed.Future readers of the document will then encounter those links in the normal course of their reading.
- Fine-grain authorization: the content delivered to a
student can be made conditional on any information encoded in the
student's record. Some uses of this capability:
- Students could be given a questionairre about their academic background at the start of the semester, and course content could subsequently be tailored to different backgrounds. In a programming course, for example, engineering and science students might be provided with different examples than students from the humanities.
- Course announcements can be made selective to students who have already read certain documents or completed certain assignments.
- Students assigned to different project groups can be given information specific to that group.
- Additional review material or practice exercises might be presented to students who did poorly on an earlier assignment.
Status
AXLE is now being used to host 3 web courses, with two more in development, plus a variety of websites for tradtitional lecture courses.