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Status: stable
Last release: 1.05 (2008/04/01)
License: GPL

SemWeb is an open-source library written in C# for Mono or Microsoft's .NET 1.1/2.0. The library can be used for reading and writing RDF (XML, N3), keeping RDF in persistent storage (memory, MySQL, etc.), querying persistent storage via simple graph matching and SPARQL, and making SPARQL queries to remote endpoints. Limited RDFS and general-purpose inferencing is also possible. SemWeb's API is straight-forward and flexible.

SemWeb was first released in June 2005 and has been more recently tested with triple stores of over 1 billion statements (see see this). The core features, like reading/writing RDF in XML and N3, persistent SQL-backed storage, and SPARQL queries, are pretty solid. Peripheral features like RDFS reasoning and backward-chaining reasoning are working, but less tested and less complete. The library has no particular tools for OWL schema. It operates at the level of RDF triples only.

SPARQL support is based on Ryan Levering's SPARQL implementation in Java (with some bug fixes and performance improvements that I hope to get up-stream), converted to .NET with IKVM (IKVM was written by Jeroen Frijters). The Euler class for general-purpose inferencing is adapted from Jos De Roo's JavaScript Euler inferencing engine.

SemWeb is licensed primarily under the terms of the GNU GPL (version 2 or later), but parts are dual-licensed under both the GNU GPL and the Creative Commons Attribution license.