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Requiring Selections On The Date Dimension In Power BI Copilot AI Instructions

Without a doubt the most important new feature in Power BI Copilot is AI Instructions: it opens up an immense number of possibilities but it also starts off as a blank slate, which raises the question of what you should do with this feature as much as how you should do it. The official documentation is very good but I think this is one of those features where the best practices only emerge after everyone has used it in the real world for a while. In an attempt to kick start this process of working out what you should do with AI Instructions I thought I’d start a series of blog posts on this subject. I don’t pretend to know all the answers, I just want to spark some debate and learn in public.

The first thing that I wanted to write about is something it has never been possible to do in Copilot up to now: force end users to always make a selection on the Date dimension.

Consider the following semantic model built from my favourite open dataset, the UK Land Registry Price Paid data, which contains details of of all the real estate transactions in England and Wales:

The Transactions fact table contains one row for each real estate transaction, including the address of the property sold and how much money was paid for it; the Property Types table contains one row for each property type (detached, sem-detached, terraced and other); and the Date dimension table is, well, a date dimension table. There are two explicit measures:

Average Price Paid = AVERAGE('Transactions'[Price])
Count Of Transactions = COUNTROWS('Transactions')

Now consider the following prompt (used with only the “answer questions about the data” skill selected in the Copilot pane in Desktop):

Show count of transactions by property type

It gives you the following result:

It’s correct, it’s exactly what I asked for, but is it useful? No: the Transactions fact table contains all the data that is currently available for 2025, from January 1st 2025 to 30th April 2025. So the visual above shows the count of transactions broken down by property type for a totally arbitrary date range that isn’t obvious to the user.

If you were building a report from this semantic model and wanted to display a visual like the one above you would always have a slicer or filter somewhere that allowed the end user to select a date or date range. Therefore it makes sense to require end users to select something on the Date dimension table if they are querying using Copilot, and remind them to do so if they do not select something.

There’s another rule to consider here. Looking at the Date dimension table you can see that the Month column only contains the name of the month:

If there was data from multiple years in the Transactions table (there isn’t in this case, but there could be if I included older data) then it wouldn’t make sense to show data for, say, “January” if that included Januarys from different years. One way to stop this from happening would be to change the values in the Month column to include the year along with the month name, but this is also something that can be handled with AI Instructions.

Here are some instructions that I came up with to implement these two rules:

## Instructions about which columns must be selected in different scenarios
The user must always specify a filter on either date, month or year in their question. If they do not, you must ask them to specify a filter on either a date, a combination of month and year, or a year. If you suggest a date, month or year filter to the end user you must only suggest selections between January 1st 2025 and April 30th 2025.
If the user asks for data filtered by a month they must always specify a year as well.

With these instructions in place, the prompt above is met with a request to specify a year, month or date filter like so:

Selecting the last of the suggested prompts gives this:

There are two things I would like to improve about this. First, the screenshot above shows the date March 15th 2025 in US date format as “3/15/2025” and I couldn’t find a way to stop this. Sigh, American software. I’ll ask to get this fixed. Second, in the instructions above you can see that I hard coded the date range of January 1st 2025 to April 30th 2025; I wanted to make this data-driven and created some measures to get the minimum and maximum dates from the Transactions table, but I couldn’t get Copilot to use them.

To show how the second rule is handled, the prompt:

Show count of transactions by property type for January

Returns the following:

Unfortunately I couldn’t find a way to reliably stop Copilot suggesting months in 2024 and 2023 in the suggested prompts. Maybe as my prompt engineering skills improve I’ll get better at this.

For more complex semantic models there could be other dimensions where a user should always make a selection – for example, if you’re doing currency conversion in your model you might want end users to always select a currency to convert to. The rules you use in AI Instructions should be similar to these though.

That’s enough for now. I have a list of other ideas for scenarios to handle with AI Instructions for future blog posts but if you have some suggestions, please leave a comment below.