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As you say, relational databases are designed for, essentially, answering queries. Rete, I would rather say, is designed for the specific task of materialized view maintenance (i.e., keeping updated the results of a query, once new changes to the data are applied). Of course, you can answer queries by building a materialized view of them, and this is why SQL ...


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Regarding the first question, as you have said in the comments, you can define a relational algebra intersection with other relational algebra operators. Anyway, relational-algebra union is usually considered a relational algebra basic operator (that cannot be defined with other relational algebra operators). Regarding monotonicity, we say that a query is ...


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I will try to answer your question limiting to Datalog without recursive predicates. Indeed, I suspect that recursive predicates are beyond conjunctive queries (conjunctive queries are a subset of FOL, and Datalog with recursion can compute Transitive Closures, which are impossible to express in FOL). Furthermore, I will assume that all derived datalog ...


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