Tannen has contributed to the principles of both programming languages and databases and also to the unification of the two subjects. One of Tannen’s major contributions is the use of
structural recursion to define a query language for nested relations. This not only provided a basis for query optimization on nested relations, it became – through the use of
comprehensions – a standard technique for embedding relational databases in programming languages. Another is the invention of provenance semirings which give a generalization of many adjuncts to relational databases, such as
probabilistic databases,
c-tables and bag semantics as well as providing a general formalism for data provenance. In addition to databases and programming languages, Tannen has contributed to bioinformatics and to systematic and evolutionary biology. On May 24 and 25 2024, a festschrift was held in Val Tannen's honor at the University of Pennsylvania. == Awards and honors ==