querytaal

Querytaal is a declarative query language designed to retrieve and transform data from heterogeneous data sources. The name blends the English word query with the Dutch word taal meaning language, reflecting its aim to provide a common querying medium across systems such as relational databases, document stores, and time-series stores.

Design goals emphasize readability, safety, and portability. Core syntax resembles SQL with clauses like SELECT, FROM, and WHERE, but includes domain-specific extensions for cross-source joins and structured output. Queries can use explicit typing or type inference, support parameterization, and may offer hints for optimization. Implementations vary, but many target a common intermediate representation for engine-agnostic execution.

Key features typically include a strong type system with schema introspection, support for nested data, filtering, aggregations, and window operations. Some variants provide streaming results, deterministic semantics, and robust error reporting. Adapters or connectors to common data stores are often included to facilitate federated queries and data integration.

Common use cases include data integration, federated analytics, business intelligence, and ad hoc data exploration across multiple sources. The ecosystem ranges from open-source reference implementations to vendor-specific adaptations and tooling.

History and status: Querytaal originated in open discussions during the 2010s as a cross-source querying concept. Since then, several implementations and proposals have appeared, with ongoing efforts toward interoperability and standardization.