Exploring Decision Tables – A Tasty Use Case

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I often find that the best way to explore or explain a visual model is to use a non-IT example. In fact, there are all kinds of processes and decisions outside the IT realm that could benefit from the application of visual modeling processes! Once you start using models and getting more familiar and comfortable with them, I bet you’ll start finding many different applications for them.

Hands full of grapes

Where I live, I’m fortunate to be surrounded by many small family-owned vineyards. Visiting them and tasting as wide a variety of local wines as possible is my new hobby. I wanted to know more about the business of growing grapes and making wine, so of course I bought a book. It’s a lot more complicated than I realized. There’s a lot of science and even math in the process!

Harvesting Grapes - a Use Case

One of the most important decisions a viticulturalist makes is when to harvest the grapes. Given that the growing conditions will be a little different every year, it’s a complicated decision matrix to get as close to ideal ripeness as possible given that perfection almost never happens in real life. And of course, ideal is different for red and white grapes. I decided to make a decision table to model this.

A Few Definitions

Brix – A measurement of the percentage of sugar present in the grapes. This is usually done by taking a sampling of grapes, crushing them, and using a hydrometer to measure the sugar content of the juice.

Titratable Acidity (TA) – A measurement of the tartaric acid content of the grapes. This is done with a test kit or by taking a sample to a wine laboratory if you happen to have one in your neighborhood.

pH – A measurement of the free hydrogen ions in the grape juice. A pH meter is used to make a more accurate measurement than the familiar paper strips.

And for those of us who have forgotten everything we learned in math class (like me), a reminder that means approximately and means approaching.

Using the Decision Table

Generally speaking, as the sugar content increases, the acidity will drop. There’s an ideal range for harvesting grapes. The Brix:TA ratio is the key thing to consider, but the pH is used as a check because if the pH gets too high, the wine will be ruined no matter what the Brix:TA measurement is. Some years, the grapes just don’t hit the ideal condition. Then the vintner has options for making adjustments in the wine-making process, but that’s a whole other article (or book)!

To read the decision table, note that each unique combination of conditions, called a rule, is read as a column, and each rule has one or more outcomes indicated. Our decision table is pretty simple, because there are only two possible outcomes, and they are mutually exclusive. I suppose in real life, there’s another outcome called “throw the grapes in the compost heap”, but let’s hope that doesn’t happen to our farmer. 

As you can see in the table above, if the Brix:TA ratio falls outside of the ideal, the determination of whether to harvest or wait depends on the pH. Since soil types will impact the pH, a viticulturalist will, through the process of testing year after year, learn how these metrics will trend for their specific location.

Whether you’re learning a new type of visual model or looking for ways to teach visual models to your team, I encourage you to explore one or more creative use cases to really dig into the model and experiment with how to apply it best in different scenarios. Then when you’re working on a project and dealing with an interesting challenge, you’ll know what models will be the most useful. For a deeper dive into how to create decision tables, take a look at this blog post from Candase Hokanson. For a thorough exploration of visual models, check out Visual Models for Software Requirements. And if you’d like to learn more about wine-making, From Vines to Wines is a good read and the source for the information in my decision table. 

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