It should not return a File but an OutputStream instead. I'd call it generate rather than build. And remove outputDirectory. And mention it's generating an image. so: ChartImageGenerator.OutputStream generate(DataSource, Map);

I don't understand why it doesn't have any method.

Simpler Data Visualization Protovis aims to bridge the gap between computer scientists and visual artists. By Kate Greene There are many ways to slice and dice data to better understand what it means. Software like Microsoft's Excel offers a simple way to create charts and graphs, while more complex applications, such as IBM's Many Eyes<http://manyeyes.alphaworks.ibm.com/manyeyes/>s/>, provide more interesting ways to visualize more complex data<http://technologyreview.com/communications/18516/>6/>. Specialized programming languages can do more by tweaking the design of visualizations. But these languages tend to be difficult for non-experts to use. Now researchers at Stanford are offering a suite of tools called Protovis<http://vis.stanford.edu/protovis/>that streamline the process of building data visualizations. The tools still require knowledge of programming but are designed to be easier to implement for someone without programming experience, says creator Jeff Heer<http://jheer.org/>g/>, a professor of computer science at Stanford. Heer says that the level of programming required to use and modify the tools is slightly above that of HTML but easier than JavaScript, a common Web scripting language. One of the main benefits of Protovis, according to Heer, is that it is structured in such a way that a person who thinks first in terms of visualizations and then in terms of data should be able to find it easy enough to use. Instead of having to focus on how to structure code for the program, Protovis lets a user create simple building blocks, such as the colors and shapes needed for the visualization, then piece the blocks together to define the complete picture. "With Protovis, you think first and foremost in visual marks on a page," Heer says. "It is our belief that this would make visualizations easier to learn and easier to modify." One example of the type of visualizations that are made easier with Protovis is called Job Voyager <http://flare.prefuse.org/apps/job_voyager>. It was created by Heer to display changing trends in employment in U.S. census data over the past century. Different types of jobs are shown in shaded areas in two different colors corresponding to male and female workers. Throughout most of the U.S. census data (from 1850 to 2000), farming was the most popular profession by far. Compared to other visualization tools, such as Prefuse or Flare, Heer says that Protovis allowed Job Voyager to be created in a fraction of the time and using a fifth of the amount of code. Heer notes that modern-data visualizations are often designed for the Web and tend to be dynamic. In the case of Job Voyager, a user can, for instance, click on a filter to see only how women's professions have changed over time. Or she can examine the ebb and flow of machinist jobs over the years. Martin Wattenberg <http://www.bewitched.com/>, who developed Many Eyes with his IBM colleague Fernanda Viegas <http://fernandaviegas.com/>, thinks that visualization is becoming an essential medium of expression, especially online. "It may be the photojournalism of the 21st century," he says. Wattenberg adds that "a system like Protovis, which lets developers easily customize Web-based visualizations, has the potential to play an important role in the adoption of this technology." Protovis is currently in an alpha release but has already been picked up by the Mozilla Foundation, and it will appear in an upcoming version of its Thunderbird e-mail client as a way to visualize e-mail data, Heer says. Copyright Technology Review 2009.