Virtuoso Universal Server is a

middleware Middleware is a type of computer software that provides services to software applications beyond those available from the operating system. It can be described as "software glue". Middleware makes it easier for software developers to implement ...

and

database engine A database engine (or storage engine) is the underlying software component that a database management system (DBMS) uses to create, read, update and delete (CRUD) data from a database. Most database management systems include their own applicati ...

hybrid that combines the functionality of a traditional

relational database management system A relational database is a (most commonly digital) database based on the relational model of data, as proposed by E. F. Codd in 1970. A system used to maintain relational databases is a relational database management system (RDBMS). Many relati ...

(RDBMS),

object–relational database An object–relational database (ORD), or object–relational database management system (ORDBMS), is a database management system (DBMS) similar to a relational database, but with an object-oriented database model: objects, classes and inherit ...

(ORDBMS), virtual database, RDF,

XML Extensible Markup Language (XML) is a markup language and file format for storing, transmitting, and reconstructing arbitrary data. It defines a set of rules for encoding documents in a format that is both human-readable and machine-readable. T ...

, free-text, web application server and

file server In computing, a file server (or fileserver) is a computer attached to a network that provides a location for shared disk access, i.e. storage of computer files (such as text, image, sound, video) that can be accessed by the workstations that are ab ...

functionality in a single system. Rather than have dedicated servers for each of the aforementioned functionality realms, Virtuoso is a "universal server"; it enables a single multithreaded server process that implements multiple protocols. The

free and open source Free and open-source software (FOSS) is a term used to refer to groups of software consisting of both free software and open-source software where anyone is freely licensed to use, copy, study, and change the software in any way, and the source ...

edition of Virtuoso Universal Server is also known as OpenLink Virtuoso. The software has been developed by OpenLink Software with Kingsley Uyi Idehen and Orri Erling as the chief software architects.

Database structure

Core database engine

Virtuoso provides an extended object–relational model, which combines the flexibility of relational access with

inheritance Inheritance is the practice of receiving private property, titles, debts, entitlements, privileges, rights, and obligations upon the death of an individual. The rules of inheritance differ among societies and have changed over time. Of ...

, run time data typing, late binding, and identity-based access. Virtuoso Universal Server database includes physical file and in memory storage and operating system processes that interact with the storage. There is one main process, which has listeners on a specified port for

HTTP The Hypertext Transfer Protocol (HTTP) is an application layer protocol in the Internet protocol suite model for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide We ...

SOAP Soap is a salt of a fatty acid used in a variety of cleansing and lubricating products. In a domestic setting, soaps are surfactants usually used for washing, bathing, and other types of housekeeping. In industrial settings, soaps are us ...

, and other protocols.

Architecture

Virtuoso is designed to take advantage of operating system threading support and multiple CPUs. It consists of a single process with an adjustable pool of threads shared between clients. Multiple threads may work on a single index tree with minimal interference with each other. One cache of database pages is shared among all threads and old dirty pages are written back to disk as a background process. The database has at all times a clean checkpoint state and a delta of committed or uncommitted changes to this checkpointed state. This makes it possible to do a clean backup of the checkpoint state while transactions proceed on the commit state. A transaction log file records all transactions since the last checkpoint. Transaction log files may be preserved and archived for an indefinite time, providing a full, recoverable history of the database. A single set of files is used for storing all tables. A separate set of files is used for all temporary data. The maximum size of a file set is 32 terabytes, for 4G × 8K pages.

Locking

Virtuoso provides dynamic locking, starting with row level locks and escalating to page level locks when a cursor holds a large percentage of a page's rows or when it has a history of locking entire pages. Lock escalation only happens when no other transactions hold locks on the same page, hence it never deadlocks. Virtuoso SQL provides means for exclusive read and for setting transaction isolation.

Transactions

All four levels of isolation are supported: Dirty read, read committed, repeatable read and serializable. The level of isolation may be specified operation by operation within a single transaction. Virtuoso can also act as a

resource manager Resource refers to all the materials available in our environment which are technologically accessible, economically feasible and culturally sustainable and help us to satisfy our needs and wants. Resources can broadly be classified upon their a ...

and/or transaction coordinator under Microsoft's Distributed Transaction Coordinator ( MS DTC) or the XA standard.

Data integrity

Virtuoso ORDBMS database supports entity integrity and referential integrity. Virtuoso ensures that relationships between records in related tables are valid by enforcing referential integrity. Integrity constraints include: * NOT NULL – Within the definition of a table, Virtuoso allows data to contain a NULL value. This NULL value is not really a value at all and is considered an absence of value. The constraint of NOT NULL forces a value to be given to a column. *

Unique key In relational database management systems, a unique key is a candidate key that is not the primary key of the relation. All the candidate keys of a relation can uniquely identify the records of the relation, but only one of them is used as the prim ...

– Uniqueness for a column or set of columns means that the values in that column or set of columns must be different from all other columns or set of columns in that table. A unique key may contain NULL values since they are by definition a unique non-valued value. *

Primary key In the relational model of databases, a primary key is a ''specific choice'' of a ''minimal'' set of attributes ( columns) that uniquely specify a tuple ( row) in a relation ( table). Informally, a primary key is "which attributes identify a recor ...

– Primary key are much like unique keys except that they are designed to uniquely identify a row in a table. They can consist of a single column or multiple columns. The primary key cannot contain a NULL value. * CHECK Constraint – Virtuoso provides on a column an integrity constraint that requires certain conditions to be met before the data is inserted or modified. If the checks are not satisfied then the transaction cannot be completed.

Data dictionary

Virtuoso stores all its information about all user objects in the database in the system catalog tables designated by db.dba*.

Components and files

Components

Virtuoso is made up of client and server components. These components typically communicate with a local or remote Virtuoso server, which include: * Virtuoso Drivers for

ODBC In computing, Open Database Connectivity (ODBC) is a standard application programming interface (API) for accessing database management systems (DBMS). The designers of ODBC aimed to make it independent of database systems and operating systems. An ...

JDBC Java Database Connectivity (JDBC) is an application programming interface (API) for the programming language Java, which defines how a client may access a database. It is a Java-based data access technology used for Java database connectivity. I ...

, ADO.NET and OLE DB * Conductor, a web-based database administration user interface * ISQL (Interactive SQL) and ISQO Utilities * Documentation and Tutorials * Samples Installations come with two databases: a default and a demo database.

History

The Virtuoso project was born in 1998 from a merger of the OpenLink data access

and Kubl RDBMS.

Kubl RDBMS

The Kubl ORDBMS was one of a list of

relational database systems Informix Corporation was a software company located in Menlo Park, California. It was a developer of relational database software for computers using the Unix, Microsoft Windows, and Apple Macintosh operating systems. Timeline * 1980: Rela ...

with roots in

Finland Finland ( fi, Suomi ; sv, Finland ), officially the Republic of Finland (; ), is a Nordic country in Northern Europe. It shares land borders with Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of Bot ...

. This list also includes

MySQL MySQL () is an open-source relational database management system (RDBMS). Its name is a combination of "My", the name of co-founder Michael Widenius's daughter My, and "SQL", the acronym for Structured Query Language. A relational database ...

InnoDB InnoDB is a storage engine for the database management system MySQL and MariaDB. Since the release of MySQL 5.5.5 in 2010, it replaced MyISAM as MySQL's default table type. It provides the standard ACID-compliant transaction features, along ...

, and Solid RDBMS/ Solid Technologies. As is the case with most technology products, key personnel behind OpenLink Virtuoso, InnoDB, and

Solid Solid is one of the four fundamental states of matter (the others being liquid, gas, and plasma). The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structur ...

share periods of professional overlap that provide noteworthy insight into the history of database technology development in Finland. Heikki Tuuri (creator of InnoDB),

Ora Lassila Ora Lassila is a Finnish computer scientist who lives in the U.S. and works as a technologist at Amazon Web Services. He has been conducting research into the Semantic Web since 1996, and was co-author, with Tim Berners-Lee and James Hendler, of ...

(W3C and Nokia Research, a technology lead and visionary in the areas RDF and Semantic Web in general alongside

Tim Berners-Lee Sir Timothy John Berners-Lee (born 8 June 1955), also known as TimBL, is an English computer scientist best known as the inventor of the World Wide Web. He is a Professorial Fellow of Computer Science at the University of Oxford and a profes ...

), and Orri Erling (Virtuoso Program Manager at OpenLink Software) all worked together in a startup company called Entity Systems in Finland – where they were developing

Common Lisp Common Lisp (CL) is a dialect of the Lisp programming language, published in ANSI standard document ''ANSI INCITS 226-1994 (S20018)'' (formerly ''X3.226-1994 (R1999)''). The Common Lisp HyperSpec, a hyperlinked HTML version, has been derived fr ...

and

Prolog Prolog is a logic programming language associated with artificial intelligence and computational linguistics. Prolog has its roots in first-order logic, a formal logic, and unlike many other programming languages, Prolog is intended primarily ...

development environments for the early generation of PC's circa. 1986–88. Later, Orri Erling worked with VIA International, the developer of VIA/DRE in designing a

LISP A lisp is a speech impairment in which a person misarticulates sibilants (, , , , , , , ). These misarticulations often result in unclear speech. Types * A frontal lisp occurs when the tongue is placed anterior to the target. Interdental lispin ...

-based

object-oriented Object-oriented programming (OOP) is a programming paradigm based on the concept of "objects", which can contain data and code. The data is in the form of fields (often known as attributes or ''properties''), and the code is in the form of ...

data access layer atop the company's

DBMS In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases ...

product. The core development team of VIA, following the company's demise in 1992, went on to found Solid Technologies under the direction of Artturi Tarjanne. Heikki Tuuri worked at

for a while before starting his own

database In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases ...

development project which became InnoDB (acquired by

Oracle An oracle is a person or agency considered to provide wise and insightful counsel or prophetic predictions, most notably including precognition of the future, inspired by deities. As such, it is a form of divination. Description The word ...

in 2005). Orri Erling started his own DBMS development work in 1994, which was to become Kubl. Development of Kubl was initially financed by Infosto Group, publisher of Finland's largest free ads paper, as part of their in-house software development project for their on-line services. The on-line version of '' Keltainen Pörssi'' was at one time said to be Finland's most popular web site with 500,000 registered users. The Kubl database was prominently displayed in a ''"Powered by Kubl"'' logo on the search results. A free trial version of Kubl was made available for download on November 7, 1996. Kubl was marketed as a high performance lightweight database for embedded use; the development aim was to achieve top scores in Transactions Per Second tests. Pricing of the product was especially favorable to

Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, whi ...

users with a Linux license priced at $199. Kubl became the cornerstone of OpenLink Virtuoso, after the technology paths of Kingsley Uyi Idehen and Orri Erling crossed in 1998, leading to the acquisition of Kubl by OpenLink Software.

Functionality realms

Virtuoso's functionality covers a broad range of traditionally distinct realms in a single product offering. These functional realms include: *

Object–relational database An object–relational database (ORD), or object–relational database management system (ORDBMS), is a database management system (DBMS) similar to a relational database, but with an object-oriented database model: objects, classes and inherit ...

engine for ( SQL,

, RDF and

plain text In computing, plain text is a loose term for data (e.g. file contents) that represent only characters of readable material but not its graphical representation nor other objects (floating-point numbers, images, etc.). It may also include a limit ...

) * Web services

computing platform A computing platform or digital platform is an environment in which a piece of software is executed. It may be the hardware or the operating system (OS), even a web browser and associated application programming interfaces, or other underlying so ...

Web Web most often refers to: * Spider web, a silken structure created by the animal * World Wide Web or the Web, an Internet-based hypertext system Web, WEB, or the Web may also refer to: Computing * WEB, a literate programming system created by ...

application server An application server is a server that hosts applications or software that delivers a business application through a communication protocol. An application server framework is a service layer model. It includes software components available to a ...

Web content management system A web content management system (WCM or WCMS) is a software content management system (CMS) specifically for web content. It provides website authoring, collaboration, and administration tools that help users with little knowledge of web programm ...

(WCMS) *

NNTP The Network News Transfer Protocol (NNTP) is an application protocol used for transporting Usenet news articles (''netnews'') between news servers, and for reading/posting articles by the end user client applications. Brian Kantor of the Univers ...

-based discussion management * Replication of homogeneous and heterogeneous data *

Mail Storage Mail storage is a type of on-demand self storage whereby customers send items by mail or delivery service (usually by the box) to be stored at a central location. It may be a viable option for people who prefer 'pay-as-you-go' storage, in which on ...

Sink and (

POP3 In computing, the Post Office Protocol (POP) is an application-layer Internet standard protocol used by e-mail clients to retrieve e-mail from a mail server. POP version 3 (POP3) is the version in common use, and along with IMAP the most common ...

) service proxy * DataPortability

Protocols implemented

Virtuoso supports a broad range of industry standard Web & Internet protocols that includes:

WebDAV WebDAV (Web Distributed Authoring and Versioning) is a set of extensions to the Hypertext Transfer Protocol (HTTP), which allows user agents to collaboratively author contents ''directly'' in an HTTP web server by providing facilities for con ...

CalDAV Calendaring Extensions to WebDAV, or CalDAV, is an Internet standard allowing a client to access and manage calendar data along with the ability to schedule meetings with users on the same or on remote servers. It lets multiple users in diff ...

CardDAV vCard Extensions to WebDAV (CardDAV) is an address book client/server protocol designed to allow users to access and share contact data on a server. The CardDAV protocol was developed by the IETF and was published as in August 2011. CardDAV is ...

, SOAP,

UDDI Web Services Discovery provides access to software systems over the Internet using standard protocols. In the most basic scenario there is a ''Web Service Provider'' that publishes a service and a ''Web Service Consumer'' that uses this service. ...

, WSDL, WS-Policy,

WS-Security Web Services Security (WS-Security, WSS) is an extension to SOAP to apply security to Web services. It is a member of the Web service specifications and was published by OASIS. The protocol specifies how integrity and confidentiality can be enfo ...

WS-ReliableMessaging WS-ReliableMessaging describes a protocol that allows SOAP messages to be reliably delivered between distributed applications in the presence of software component, system, or network failures. The original specification was written by BEA Syste ...

, WS-Routing, WS-Referral, WS-Attachment,

WS-BPEL The Web Services Business Process Execution Language (WS-BPEL), commonly known as BPEL (Business Process Execution Language), is an OASIS standard executable language for specifying actions within business processes with web services. Process ...

SyncML SyncML (Synchronization Markup Language) is the former name for a platform-independent information synchronization standard. The project is currently referred to as ''Open Mobile Alliance Data Synchronization and Device Management''. The purpose o ...

GData Gdata may refer to: * GData, the Google Google LLC () is an American multinational technology company focusing on search engine technology, online advertising, cloud computing, computer software, quantum computing, e-commerce, artificial ...

SPARQL SPARQL (pronounced " sparkle" , a recursive acronym for SPARQL Protocol and RDF Query Language) is an RDF query language—that is, a semantic query language for databases—able to retrieve and manipulate data stored in Resource Description ...

, SPARUL, NNTP

API support

For the database application developer and systems integrator, Virtuoso implements a variety of industry standard data access APIs (client and server) that includes: ODBC, JDBC, OLE DB, ADO.NET,

ADO.NET Entity Framework Entity Framework (EF) is an open source object–relational mapping (ORM) framework for ADO.NET. It was originally shipped as an integral part of .NET Framework, however starting with Entity Framework version 6.0 it has been delivered separately ...

XMLA XML for Analysis (XMLA) is an industry standard for data access in analytical systems, such as online analytical processing (OLAP) and data mining. XMLA is based on other industry standards such as XML, SOAP and HTTP. XMLA is maintained by XMLA C ...

Content syndication and interchange format support

For the Web application developer and content syndicate(s) publishers, and consumers, Virtuoso supports standards such as:

Atom Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. Every solid, liquid, gas, a ...

, RSS 2.0, RSS 1.0,

OPML OPML (Outline Processor Markup Language) is an XML format for outlines (defined as "a tree, where each node contains a set of named attributes with string values"). Originally developed by UserLand as a native file format for the outliner appl ...

XBEL The XML Bookmark Exchange Language (XBEL), is an open XML standard for sharing Internet URIs, also known as ''bookmarks'' (or ''favorites'' in Internet Explorer). An example of XBEL use is thXBELiciousapplication, which stores Del.icio.us bookmar ...

FOAF FOAF (an acronym of friend of a friend) is a machine-readable ontology describing persons, their activities and their relations to other people and objects. Anyone can use FOAF to describe themselves. FOAF allows groups of people to describe s ...

, SIOC.

Query language support

SQL,

(with numerous extensions),

XQuery XQuery (XML Query) is a query and functional programming language that queries and transforms collections of structured and unstructured data, usually in the form of XML, text and with vendor-specific extensions for other data formats (JSON, b ...

(implementation of Core functions library is seriously incomplete),

XPath XPath (XML Path Language) is an expression language designed to support the query or transformation of XML documents. It was defined by the World Wide Web Consortium (W3C) and can be used to compute values (e.g., strings, numbers, or Boolean v ...

(1.0 only),

XSLT XSLT (Extensible Stylesheet Language Transformations) is a language originally designed for transforming XML documents into other XML documents, or other formats such as HTML for web pages, plain text or XSL Formatting Objects, which may subseq ...

(1.0 only)

Schema definition language support

SQL's Data Definition Language,

XML Schema An XML schema is a description of a type of XML document, typically expressed in terms of constraints on the structure and content of documents of that type, above and beyond the basic syntactical constraints imposed by XML itself. These constra ...

Usage scenarios

Virtuoso is a solution for the following

system integration System integration is defined in engineering as the process of bringing together the component sub- systems into one system (an aggregation of subsystems cooperating so that the system is able to deliver the overarching functionality) and ensurin ...

challenges: * Enterprise Information Integration (EII) * Programming Language Independent

Web application A web application (or web app) is application software that is accessed using a web browser. Web applications are delivered on the World Wide Web to users with an active network connection. History In earlier computing models like client-serv ...

deployment * Monolithic application decomposition that leverages the principles of

service-oriented architecture In software engineering, service-oriented architecture (SOA) is an architectural style that focuses on discrete services instead of a monolithic design. By consequence, it is also applied in the field of software design where services are provid ...

* Web service based

enterprise application integration Enterprise application integration (EAI) is the use of software and computer systems' architectural principles to integrate a set of enterprise computer applications. Overview Enterprise application integration is an integration framework comp ...

via a significant amount of WS-* protocols support *

Business process management Business process management (BPM) is the discipline in which people use various methods to discover, model, analyze, measure, improve, optimize, and automate business processes. Any combination of methods used to manage a company's business p ...

via BPEL * Semantic Web Data Spaces Generation * Deployment platform for injecting RDF-based

Linked Data In computing, linked data (often capitalized as Linked Data) is structured data which is interlinked with other data so it becomes more useful through semantic queries. It builds upon standard Web technologies such as HTTP, RDF and URIs, but ...

into the Semantic Data Web

Related technology areas

Data management

Relational database management system A relational database is a (most commonly digital) database based on the relational model of data, as proposed by E. F. Codd in 1970. A system used to maintain relational databases is a relational database management system (RDBMS). Many relati ...

* List of relational database management systems *

Comparison of object–relational database management systems This is a comparison of object–relational database management systems (ORDBMSs). Each system has at least some features of an object–relational database; they vary widely in their completeness and the approaches taken. The following tables c ...

Comparison of relational database management systems The following tables compare general and technical information for a number of relational database management systems. Please see the individual products' articles for further information. Unless otherwise specified in footnotes, comparisons are ba ...

Enterprise application, information, and data integration

Web 2.0 Web 2.0 (also known as participative (or participatory) web and social web) refers to websites that emphasize user-generated content, ease of use, participatory culture and interoperability (i.e., compatibility with other products, systems, and ...

Enterprise service bus An enterprise service bus (ESB) implements a communication system between mutually interacting software applications in a service-oriented architecture (SOA). It represents a software architecture for distributed computing, and is a special varia ...

Service-oriented architecture In software engineering, service-oriented architecture (SOA) is an architectural style that focuses on discrete services instead of a monolithic design. By consequence, it is also applied in the field of software design where services are provid ...

Enterprise application integration Enterprise application integration (EAI) is the use of software and computer systems' architectural principles to integrate a set of enterprise computer applications. Overview Enterprise application integration is an integration framework comp ...

Data integration Data integration involves combining data residing in different sources and providing users with a unified view of them. This process becomes significant in a variety of situations, which include both commercial (such as when two similar companies ...

* Open Semantic Framework * Web service * Semantic Web * Business Integration Severs Comparison Matrix

Related products and tools

In addition to Virtuoso, OpenLink Software produces several related tools and applications: * OpenLink Data Spaces – a Virtuoso-based platform for cost-effective creation and management of Semantic Web /

Web presence. It provides a data junction box for integrating data across third party

Social network service A social networking service or SNS (sometimes called a social networking site) is an online platform which people use to build social networks or social relationships with other people who share similar personal or career content, interests, ac ...

Blog A blog (a Clipping (morphology), truncation of "weblog") is a discussion or informational website published on the World Wide Web consisting of discrete, often informal diary-style text entries (posts). Posts are typically displayed in Reverse ...

File sharing File sharing is the practice of distributing or providing access to digital media, such as computer programs, multimedia (audio, images and video), documents or electronic books. Common methods of storage, transmission and dispersion include r ...

, Shared &

Social bookmarking Social bookmarking is an online service which allows users to add, annotate, edit, and share bookmarks of web documents. Many online bookmark management services have launched since 1996; Delicious, founded in 2003, popularized the terms "social ...

Wiki A wiki ( ) is an online hypertext publication collaboratively edited and managed by its own audience, using a web browser. A typical wiki contains multiple pages for the subjects or scope of the project, and could be either open to the pub ...

E-mail Electronic mail (email or e-mail) is a method of exchanging messages ("mail") between people using electronic devices. Email was thus conceived as the electronic (digital) version of, or counterpart to, mail, at a time when "mail" meant ...

, Photo Sharing, RSS 2.0,

, and RSS 1.1 Content Aggregation services. In addition, to its third party integration functionality, it also includes its own rich collection of

compliant distributed collaborative applications, across each of the aforementioned Web application realms. * Universal Data Access Drivers – High-performance data access drivers for ODBC, JDBC, ADO.NET, and OLE DB that provide transparent access to enterprise databases across multiple platforms and databases.

Platforms

Virtuoso is supported on a number of 32- and 64-bit platforms including cross-platform

Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for se ...

, UNIX ( HP,

AIX Aix or AIX may refer to: Computing * AIX, a line of IBM computer operating systems *An Alternate Index, for a Virtual Storage Access Method Key Sequenced Data Set * Athens Internet Exchange, a European Internet exchange point Places Belgiu ...

, Sun, DEC, BSD, SCO), Linux (

Red Hat Red Hat, Inc. is an American software company that provides open source software products to enterprises. Founded in 1993, Red Hat has its corporate headquarters in Raleigh, North Carolina, with other offices worldwide. Red Hat has become a ...

SUSE SUSE ( , ) is a German-based multinational open-source software company that develops and sells Linux products to business customers. Founded in 1992, it was the first company to market Linux for enterprise. It is the developer of SUSE Linux Ent ...

) and

macOS macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and la ...

Licensing

In April 2006, a

free software Free software or libre software is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versions. Free software is a matter of liberty, n ...

version of Virtuoso was made available under the

GNU General Public License The GNU General Public License (GNU GPL or simply GPL) is a series of widely used free software licenses that guarantee end users the four freedoms to run, study, share, and modify the software. The license was the first copyleft for general ...

version 2. The software is now available in Commercial and Open Source license variants.

References

External links

* {{official website, http://virtuoso.openlinksw.com/ Atom (Web standard) Big data products Client-server database management systems Column-oriented DBMS software for Linux Cross-platform free software Cross-platform software Database engines Distributed computing architecture Document-oriented databases Enterprise application integration Free database management systems Free file sharing software Free software programmed in C Free web server software FTP server software Message-oriented middleware Metadata Middleware NewSQL NoSQL Online databases ORDBMS software for Linux MacOS database-related software Products introduced in 1998 Relational database management systems RSS Semantic Web SQL data access Structured storage Triplestores Unix Internet software Unix network-related software Web services Windows database-related software XML software XSLT processors