Using Google Visualizations to display SPARQL results
1. What is the Visualization API?
From Google: "The Google Visualization API lets you access multiple sources of structured data that you can display, choosing from a large selection of visualizations. Google Visualization API enables you to expose your own data, stored on any data-store that is connected to the web, as a Visualization compliant datasource. Thus you can create reports and dashboards as well as analyze and display your data through the wealth of available visualization applications. The Google Visualization API also provides a platform that can be used to create, share and reuse visualizations written by the developer community at large."
2. What sorts of visualizations can you make?
3. How do charts access data?
Charts can load data directly from Google Spreadsheets, and we can populate Google Spreadsheets with SPARQL results easily enough. However, this means that if the spreadsheet has not been refreshed recently, the visualization may not be up-to-date. It would be better to load the data "live" whenever a visualization is created.
It's possible to use Java Server Pages (JSP) to execute a SPARQL query, have the server process the results using custom Java code, and pass the results to the web page. It takes a long time to set up this process, and on several occasions the final result hasn't worked because of a quirk somewhere in the Google Appspot server we've been using. So this method is also less than ideal.
4. Can Google Visualizations handle data from multiple SPARQL endpoints or data sources?
The Google Visualization API has built-in functions for joining data objects (tables), so the short answer is yes. We could join the results of a SPARQL query to the data pulled from a Google spreadsheet, or we could combine the results of SPARQL queries from different endpoints. However, in practice we've run into the problem that names for elements in different data sources (country names, for example) don't match up exactly, and so some elements may get left out. Matching data from different sources will be one of the major challenges of using open data from the Semantic Web.
5. Can Google Visualizations handle aggregation?
Yes. Until SPARQL 1.1 gives us the ability to use SUM and COUNT in our queries, we can easily run basic aggregations usingGoogle's aggregation functions.
6. Can Google Visualizations be gadgetized?