The query { R| ∃T ∈ Authors(T.article=’database’ AND R.name=T.name)} fetches tuples from R where there exists at least one tuple in Authors that fulfills the condition.
- The existential quantifier (∃) indicates that there exists at least one tuple T in Authors that satisfies the condition specified within the parentheses.
- The condition specified is T.article=’database’ AND R.name=T.name, meaning that there exists a tuple T in Authors where the article attribute is ‘database’, and the name attribute of R matches the name attribute of T.