Wednesday, October 05, 2005

More on the bubble graph

Keith posted a note on the power of the different types of visualizations available in Discoverer (Making More of BI Graphs...), and mentioned the bubble graph in particular.

The bubble graph is also my favourite - and have a couple of examples to illustrate its power.

Using the data from the BI Samples (available from OTN), I have used Discoverer to create a workbook that shows me how my product categories are doing - i.e. margins, sales, and change in margin over last year. And I want to see things in perspective - margins and changes in margin will be of greater interest for those products (or product categories) for my volume sellers. I can either use this crosstab as the basis for analysis, or I can crete a bubble graph as shown below: the bubble graph is a graph subtype available under the 'Scatter/Bubble' graph type.
Click 'OK' and your graph is plotted. Simple as that - takes all of five seconds, maybe a little longer if you get distracted looking at all the other fabulous graph types Discoverer offers.
Take a look below:
- On the X-axis I have margin (the first column in my crosstab)
- On the Y-axis I have the change in margin over last year (the second column in my crosstab)
- The size of the bubble is the sales revenue measure (the third column in my crosstab above)
I should be a happy person here, reasonably speaking - most of my product categories are in the top-right quadrant, which means that not only are margins healthy, but they have also grown nicely over last year. But I do have one product category in the bottom-right quadrant - Hardware - that I may want to investigate to see if the problem can be isolated in a specific product sub-category.
Or, I may want to analyze the 'Software/Others' product category (the top most bubble) further.
If I double-click the 'Software/Other' bubble (or click its legend label on the left) I see that 'Recordable DVD Discs' are (unsurprisingly) doing good. But the rest are displaying only middling sort of performance - they are more in the left side of the box than the right. 'Recordable CDs' is in fact the laggard product sub-category here.
Drilling down the 'Recordable CDs' sub-cat tells me that my 'Jewel cases pack of 10' sell the most in this sub-cat, and aren't doing too badly. Maybe I should focus on this item to make sure I can keep its margins shored up. Or maybe I need to cut out 'CD-R pack of 10' from my product-mix since they are showing falling margins, and are likely to prove to be a drag on my bottom line.
Returning to my parent product sub-category of 'Software-Others' (by simply clicking the 'Recordable CDs' link in the legend, the one with the up-arrow).
Here I want to look at my 'star' - Recordable DVD Drives - a little more.
Yikes! Something is wrong here - while the single 'DVD-R Disc with jewel case' is a real hot seller, and with health margins too, every other product is actually giving me low single-digit margins. And two of those products are actually seeing shrinking margins. Time for action - I may want to drill to detail, to the transactional level, and see the individual sales transaction rows (and you can do that with Discoverer!).
As you can see, a bubble graph goes a long way beyond the simple (and simplistic) bar graph types - sometimes you don't need to use fancy and overly complicated visualizations to get insight into your data. The tools and the means are all right there - at your fingertips. Analyzing three different measures in a single graph is not always easy, but the bubble graph is a particularly well-suited graph for the purpose.