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...Relational query languages allow manipulation and retrieval of data from a database model supports simple powerful qls strong formal foundation based on logic allows for much optimization programming not expected to be turing complete intended used complex calculations support easy efficient access large sets two mathematical form the basis real e g sql implementation algebra more operational procedural useful representing execution plans calculus users describe what they want rather than how compute it non declarative preliminaries is applied relation instances result also instance schemas input relations are fixed schema given determined by definition language constructs positional vs named field notation easier definitions readable both in r example sailors reserves sid sname rating age our s examples dustin we ll use or lubber rusty assume that names fields results inherited yuppy guppy basic operations selection selects subset rows projection deletes unwanted columns cross product...