A “safe” query expression assures consistent results across different database schemas, ensuring domain independence.
Here are some properties and circumstances that define a “safe” query statement in relational calculus:
- The query expression should include well-defined conditions and constraints that ensure only a finite number of tuples meet the requirements.
- Specifying constraints such as “there exists a tuple” or “for all tuples” inside a defined scope helps to guarantee that the query is finite.
- The query should not contain operations that result in infinite relations or result sets.