alql

AlQL, short for Algebraic Query Language, is a theoretical and educational query language designed to express data retrieval and transformation through algebraic operations. It models queries as compositions of core relational operators plus functional mappings, prioritizing formal semantics over imperative control flow.

Origin and scope: The term arose in database theory and programming language literature in the 2000s as a tool to teach relational algebra and to explore formal query equivalence. It has no single canonical implementation, but several toy interpreters and research prototypes exist to demonstrate algebraic query construction.

Key features: Core operators correspond to selection, projection, joins, and aggregation. Queries are built by combining expressions with let bindings and function maps; the language supports nested data and higher-order mapping over collections. Semantics are defined through set-based mathematics, making it amenable to formal reasoning about correctness and optimization.

Example: A simple AlQL query might express: let Q = from p in patients, v in visits where p.id = v.patient_id and p.age > 60 return { p.name, v.diagnosis }

Relation to other languages and limitations: AlQL resembles SQL and Datalog in intent but emphasizes algebraic composition. It has limited real-world adoption and is primarily used in education and theoretical research; translating AlQL queries to executable code can be complex, and performance considerations depend on the underlying engine.