If the Web is to have a significant impact on the quality of SMET education, content developers must begin to build on each other's work. Much of the progress of modern software development is based on the concept of reusability. In the beginning, reusability often meant the use of subroutines but more recently the more powerful paradigms of object-oriented programming and component architecture have been particularly effective strategies for producing reliable and powerful software -- software that begins where previous software ended. The same underlying ideas offer promise for producing real progress in SMET education.

The keys to reusability are the concepts of educational objects and granularity. An educational object is an interchangable, complete, and self-contained unit that is designed to be used in various settings and in various ways. Such an object can be quite large (an entire course, for example) or quite small (for example, a single simulation or data set). Large objects can be built up from smaller ones. By beginning with relatively small basic objects, developers can create very flexible SMET content. Thus, the level of granularity is important. Fine granularity -- a large number of relatively small basic objects -- leads to greater reuse.

Reusability requires technical, social, economic, and legal infrastructures. Of the three, the technical infrastructure is almost certainly the easiest -- functional specifications, component architecture, metadata, object-oriented programming, and true mark-up languages are likely to play important roles. The legal and economic infrastructures are still evolving in a much larger arena. The social and institutional infrastructures may be somewhat different in the academic arena than in the larger arena. In particular, altruism may play a significant role, especially if library publication is perceived as professionally rewarding and as counting toward tenure, promotion, and merit pay.

A national digital library for SMET education will also contribute to reusability in other less obvious, but still important, ways. By providing stability and a framework encouraging the production and use of reviews and user-reports, such a library will eventually contain objects with an accumulated corpus of experience and commentary. For example, simulations that are known to be reliable and scientifically sound will become attractive candidates for reuse.

One interesting approach to reusability is the Educational Object Economy at http://trp.research.apple.com/.