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Opa is an open source programming language for developing scalable web applications. It can be used for both client-side and server-side scripting, where complete programs are written in Opa and subsequently compiled to Nodejs on the server and JavaScript on the client, with the compiler automating all communication between the two.〔Opa actually supports various server-side backends, Nodejs being the most popular one〕 Opa implements strong, static typing, which can be helpful in protecting against security issues such as SQL injections and cross-site scripting attacks. The language was first officially presented at the OWASP conference in 2010,〔(【引用サイトリンク】publisher=OWASP )〕 and the source code was released on GitHub in June 2011, under a GNU Affero General Public License. Later, the license changed to the MIT license for the framework part (library) and AGPL for the compiler so that applications written in Opa can be released under any license, proprietary or open source. == Design and features == Opa consists of a web server, a database and distributed execution engine.〔(【引用サイトリンク】title=Opa – The Scalable Open Source Cloud Language )〕 Code written in Opa is compiled to JavaScript using Node.js on the server side and to JavaScript using jQuery for cross-browser compatibility on the client side.〔(【引用サイトリンク】publisher=InfoQ )〕 The advantage of the approach compared to certain Rich Internet Application (RIA) platforms is that users are not required to install a plugin in their browser. Opa shares motivations with web frameworks, but takes a different approach.〔(【引用サイトリンク】title=InfoWorld review: Tools for rapid Web development )〕 Its designers assert that this helps Opa to avoid many security issues, like SQL injections or cross-site scripting (XSS) attacks.〔(【引用サイトリンク】title=Auch Opa ist für Cloud-Anwendungen )〕 The core language is functional and has a static type system with type inference. Opa also provides sessions which encapsulate an imperative state and communicate using message passing, similar to Erlang processes. Opa provides many structures or functions that are common in web development, as first-class objects, for instance HTML〔(【引用サイトリンク】title=Opa - a unified approach to web programming )〕 and parsers, based on Parsing Expression Grammars. Because of this adhesion between the language and web-related concepts, Opa is not intended for non-web applications (for instance desktop applications). The 0.9.0 release in February 2012 introduced database mapping technology for the non-relational, document-oriented database MongoDB, similar to object-relational mapping.〔(【引用サイトリンク】title=Hello, database )〕〔(【引用サイトリンク】title=Low-level MongoDB support )〕 The 1.1.0 release in February 2013 also added support for PostgreSQL, paving the way for the support of several SQL databases. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Opa (programming language)」の詳細全文を読む スポンサード リンク
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