Strongly-Normalizing Higher-Order Relational Queries

Language-integrated query is a powerful programming construct allowing database queries and ordinary program code to interoperate seamlessly safely. techniques rely on classical results about the nested relational calculus, stating that its can be algorithmically translated SQL, as long their result type flat relation. Cooper others advocated higher-order calculi basis for language-integrated in functional languages such Links F#. However, translation of SQL relies rewrite system which no strong normalization proof has been published: previous attempt does not deal correctly with rules duplicate subterms. This paper fills gap literature, explaining difficulty attempt, showing how extend $\top\top$-lifting approach Lindley Stark accommodate duplicating rewrites. We also show recently-introduced calculus heterogeneous mixing set multiset semantics.