The feature described in this tutorial is only available with **Commercial** or **Enterprise** AI Hub licenses.

A derived field doesn't extract data directly from a document. Instead, it constructs a new value out of the values of one or more other fields in the class.

Start with an AI Hub project that already has at least one field defined that's *not* a derived field

For this example, we'll use an app that analyzes restaurant menus

The **menu** class has two reasoning fields already defined:

- **Number of meat dishes**
- **Number of vegetarian dishes**

To add a derived field, first click **Add field**

Our new field will be called **Vegetarian friendly**

It will compare the values of the **Number of meat dishes** and **Number of vegetarian dishes** fields, and will have the value **True** if there are at least as many veg dishes as meat dishes

Name the new field [[Vegetarian friendly]]

Used to generate values based on other fields in the project or class.

Clear the value in the **Prompt** field so we can provide our own prompt

In the **Prompt** field, start our new prompt by typing [[Is]]

In the dropdown below the **Prompt** field, click **Number of vegetarian dishes**

Note that this dropdown is populated with all field names that have already been defined for this class

Number of vegetarian dishes
Number of vegetarian dishes

Continue the prompt by typing  [[ at least as big as ]]

In the dropdown, select **Number of meat dishes**

Complete the prompt by typing [[? Return True or False only.]]

The complete prompt should say: 

*Is **Number of vegetarian dishes** at least as big as **Number of meat dishes**? Return True or False only.*

Confirm that the field contains **True**, since there are at least as many veg dishes as meat dishes.

Return to the class's full schema description by clicking the back button

You should see three fields, including the new derived field

Instabase

Learn how to define derived fields, which generate values based on the value of other fields in the same document class.

Define derived fields