Equivalence of missing Properties and NULL values
I propose that we treat a missing Property and a Property with a None/NULL value the same.
- The query language syntax "has Property xy" is more meaningful, because it might in future exclude records where the Property has a NULL value.
- You cannot simply add an obligatory Property with a NULL value to prevent the error that an obligatory Property is missing.
- One could define that not having a Property and having one with a NULL value has different meanings. However, this additional meaning would not be transparent to users and add complexity. Thus, additional meaning why something is missing should be added in a more transparent way: Add Properties like "was_measured".
- Data in relational databases do not know this distinction. We would lose compatibility and force us to stay with tuple based backend structures.
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