1979/01/01 by Alfred V. Aho, Jeffrey D. Ullman · 6 citations
Computer Science · Mathematics · #Advanced Database Systems and Queries #Data Management and Algorithms #Semantic Web and Ontologies #Relational algebra #Relational calculus #Computer science #Codd's theorem #Relational database #Query language #Conjunctive query #Relational model #Universality (dynamical systems) #Programming language #Algebra over a field #Information retrieval #Mathematics #Pure mathematics
paper · pdf · doi:10.1145/567752.567763
openalex publication_date 1979/01/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/29
We consider the question of how powerful a relational query language should be and state two principles that we feel any query language should satisfy. We show that although relational algebra and relational calculus satisfy these principles, there are certain queries involving least fixed points that cannot be expressed by these languages, yet that also satisfy the principles. We then consider various extensions of relational algebra to enable it to answer such queries. Finally, we discuss our extensions to relational algebra in terms of a new programming language oriented model for queries.