Video: SPARQL-based Unit Conversion with SPIN
Here is a video on another example application of SPIN. This time we are using SPARQL rules to convert values between units of measurement. In the example we convert from centimeters to feet and cubic meters to cubic feet. Two solutions are presented: The first is using SPARQL CONSTRUCTs that have the conversion factors encoded as part of the spin:rules. The second solution is much more generic and uses a NASA units ontology (developed by TopQuadrant) to dynamically find the appropriate conversion factors. For this second solution, the video also shows how to define new SPARQL functions using SPIN, and how to use SPIN templates to encapsulate reusable queries. The video is a step-by-step tutorial and takes about 16 minutes to complete. If you haven't done so yet, you should have a look at the TopBraid Composer SPIN page to get some background and screenshots about SPIN functions and templates.
I believe this is a fine example of what can be achieved if Semantic Web technology is applied the way that it should: to share data models and knowledge together with executable semantics. SPIN might be a missing link in the Semantic Web stack, because it allows users to create and share domain-specific modeling languages that encapsulate all the background needed to build useful applications out of them.