https://trailhead.salesforce.com/content/learn/modules/apex_basics_dotnet/mapping_concepts?trailmix_creator_id=00550000006yDdKAAU&trailmix_id=prepare-for-your-salesforce-platform-developer-i-credential 

In the "Data Types" section, it lists "Data" as a primitive instead of "Date". 

Im trying to create a validation rule that makes one Picklist Field required when another Picklist Field is selected. 
For example when the Picklist Field(Status) has the value "Unqualifed"  theres another picklist field that should be required called "Rating"
Here's my sytax so far, i keep getting errors, any advise?

AND(ISPICKVAL(Status,'Unqualified'),ISNULL(Rating))