Data Visualizationwith Venn DiagramsIn this chapter s case study, (Windows 2003 server web)
Data Visualizationwith Venn DiagramsIn this chapter s case study, we show one way to use PHP to com- bine MySQL databases with graphic images. We build a completesystem that starts with a database and uses the gdlibrary to producea kind of visualization of the data. The portions of the book we drawon for this are: .Part II: We use PHP to interrogate a MySQL database. .Chapter 42 (Graphics): Our end-product is an image producedwith the gdlibrary. .Chapter 27 (Mathematics): We need a bit of trigonometry as wecreate the images. Scaled Venn DiagramsThe visualization we have in mind is something like the Venn diagram. If you ve ever been in an academic setting where set intersection wasbeing discussed, then you ve probably seen these diagrams they rethe circles that may or may not have overlapping portions represent- ing intersections. We say something like the Venn diagram, because scale has no sig- nificance in a traditional Venn diagram. If you want to illustrate thefact that there are people who use both BeOS and Windows, then youmight draw two circles of equal size (representing Windows usersand BeOS users) that happen to have a region of overlap. In our ver- sion, which you might call a scaledor proportionalVenn diagram, thesizes of both circles and intersections matter; the Windows/BeOSexample would become one large circle and one much smaller circle, with an overlap area proportional to the number of people in bothsets. (To see an example of this kind of diagram, please skip ahead toFigure 48-5.) The taskThe job of our code is to start with a database, provide a way to querythat database about sets and their overlap, and then display theresults as a scaled Venn diagram, generated by using the gdlibrary. Asa sample database, we use the pseudosurvey dataset that we used inthe HTML Graphics section of Chapter 42.4848CHAPTER …In This ChapterFrom database toimageScaled Venn diagramsPlanning the displayPutting it all together …
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