Functions Become Data: Higher-Order Lambda Functions for Database Systems

• Applicant: Professor Dr. Maximilian Schüle
• Subject Area: Data Management, Data-Intensive Systems, Computer Science Methods in Business Informatics
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 558877244

The invention of the relational model in 1970 laid the foundation for the enduring success of SQL as the data query language. Since then, support for user-defined functions has been considered an unnatural extension of relational algebra and a second-class citizen to SQL. SQL lambda expressions were introduced to allow users to customise otherwise hard-coded data mining operators, such as the distance function for k-Means clustering. However, database systems parse lambda expressions during semantic analysis, which does not allow functions as arguments. Let us break down the barrier between data and query language and let functions become first-class citizens in SQL. When functions become data, they can be stored, retrieved and executed within regular SQL queries. This proposal aims to be the logical next step for SQL lambda functions, integrating the lambda calculus into database systems by enabling higher-order logic and demonstrating its application to machine learning.

• DFG Programme: Research Grants