Basically you are free to adjust the standard db schema which is created by the ivy-core for your needs. The database table is called `IWA_TASK`.
However, be aware that in consequence the adjustment of the schema must be well known and documented within the roll-out process of your app.
... so don't do if you can avoid it. Use the 'description' or one of the customStringFields to add extended text fields which can easily be queried and displayed to end users task list.