Sunday, February 8, 2009

Using Google Chart API to Implement Harvesting Grade Book

Our department has been working on a transformative assessment approach to teaching and learning. One of the challenges of implementing the idea is to provide rich renderings to help in conceptualizing and communicating the assessment data, one of which is in a form of what we currently called the Harvesting Grade Book (See "Rich Assessment From A Harvesting Grade Book" for more information).

Currently, the graphs in the Harvesting Grade Book example are generated manually. The data is downloaded into Excel and then graphed. This manual approach though, has its limitation: the results cannot be scaled and cannot be updated in real-time. We need to find ways to automate this process.

I looked at options.  The Microsoft LogParser utility was a potential solution I investigated to address the scaling issue. For those who are not familiar with it, LogParser is powerful command line utility. It takes input from a variety of sources, such as CVS, query a SQL database and even Active Directory via LDAP, etc. The output can also be in a variety of formats, such as XML, charts, etc. I have used it to generate a number of monitoring and usage graphs for the Blackboard Learning Management System. I believe my familiarity with LogParser would enable me to apply the utility, in conjunction with a wrapper script, to automate graphs generation for the Harvesting Grade Book in batch.

In order to overcome the second limitation - real-time updates, I decided to experiment with Google Chart API. For those who are not familiar with it, the Google Chart API lets you dynamically generate chart on the fly by sending it a REST web services call (which is basically a URL which contains the chart properties and data). The service will then return you the chart as an image in PNG format. What makes this solution elegant and easy to apply is that the URL contains the data. This kind of web-based charting is far easier and efficent than the manual compilations and complications of using Excel.

For example, a radar graph like those in the Harvesting Grade Book example can be created with a URL:
Google will then return the following graph:
Perfect! And to any usage limitation concerns of using Google Chart API service, "There's no limit to the number of calls per day you can make to the Google Chart API... If you think your service will make more than 250,000 API calls per day, please let us know by mailing an estimate to ...". With a number like 250,000, I consider the scalability issue solved.

1 comment:

Mr. Mayday said...

thanks for the link!