From the website:

Web Ontology Language (OWL) is a markup language for publishing and sharing data using ontologies on the Internet. OWL is a vocabulary extension of the Resource Description Framework (RDF) and is derived from the DAML+OIL Web Ontology Language (see also DAML and OIL). Together with RDF and other components, these tools make up the Semantic Web project.

OWL represents the meanings of terms in vocabularies and the relationships between those terms in a way that is suitable for processing by software.

The OWL specification is maintained by the World Wide Web Consortium (W3C).

From the website:

This paper proposes the use of the Unified Modeling Language (UML) as a language for modelling ontologies for Web resources and the knowledge contained within them. To provide a mechanism for serialising and processing object diagrams representing knowledge, a pair of XSLT stylesheets have been developed to map from XML Metadata Interchange (XMI) encodings of class diagrams to corresponding RDF schemas and to Java classes representing the concepts in the ontologies. The Java code includes methods for marshalling and unmarshalling object-oriented information between in-memory data structures and RDF serialisations of that information. This provides a convenient mechanism for Java applications to share knowledge on the Web.

For the website:

Virtuoso is at the core a high performance object-relational SQL database. As a database, it provides transactions, a smart SQL compiler, powerful stored procedure language with optional Java and .Net server side hosting, hot backup, SQL 99 and more. It has all major data access interfaces, as in ODBC, JDBC, ADO .Net and OLE/DB.

Virtuoso has a built-in web server which can serve dynamic web pages written in Virtuoso's web page language as well as PHP, ASP .net and others. This same web server provides SOAP and REST access to Virtuoso stored procedures, supporting a broad set of WS protocols such as WS-Security, WS-Reliable Messaging and others. A BPEL4WS run time is also available as part of Virtuoso's SOA suite.

Virtuoso has a built-in WebDAV repository. This can host static and dynamic web content and optionally provides versioning. The WebDAV repository is tested to interoperate with WebDAV clients built into Windows XP, Mac OSX and others and makes Virtuoso a convenient and secure place for keeping one's files on the net. Further, Virtuoso provides automatic metadata extraction and full text searching for supported content types.

Open Virtuoso supports SPARQL embedded into SQL for querying RDF data stored in Virtuoso's database. SPARQL benefits from low-level support in the engine itself, such as SPARQL aware type casting rules and a dedicated IRI data type. This is the newest and fastest developing area in Virtuoso.

From the website:

BigOWLIM is a high-performance semantic repository, implemented in Java and packaged as a Storage and Inference Layer (SAIL) for the Sesame RDF database. BigOWLIM uses the TRREE engine to perform RDFS, OWL DLP, and OWL Horst reasoning, based on forward-chaining of entailment rules. The most expressive language supported is a combination of limited OWL Lite and unconstrained RDFS. BigOWLIM can manage billions of explicit statements on server hardware. A principle limitation of BigOWLIM is the relatively slow delete operation. The upload, reasoning, and the query evaluation proceed fast even against huge ontologies and datasets. 

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Article on use of reverse proxy in performance environments.

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