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Kepler FAQWhat is Kepler?Kepler is both a project and a Web development platform. As a project it is developing a set of general use components for Lua 5.0. As a platform it allows the creation of powerful Web applications using Lua.
Why "Kepler"?Johannes Kepler was the astronomer that first explained that the tides are caused by the Moon. "Lua" means Moon in Portuguese, so the name "Kepler" tries to hint that some new tides may soon be caused by Lua... :o)
What is Lua?Lua is a programming language that offers some very impressive set of features while keeping everything fast, small and portable. The Kepler Platform uses these features to offer a faster, smaller and more portable way to develop Web applications.
What is a Web application?Web applications (also known as Web apps) are programs that are used through a Web browser. Every time you search for something with Google, read mail with Hotmail or browse Amazon you are using a Web application. Some other examples would be discussion forums, a blog or a weather site.
What is a Web development platform?Web applications can be developed in different ways, from a hands on approach to a very structured one. A Web development platform offers the developer a number of features that make the development of Web applications a lot easier. Instead of developing the application from scratch, the developer can benefit from the building blocks of the Web platform.
Why build/use another Web development platform?There are lots of great Web development platforms out there but most, if not all of them, do not offer the same balance between power/size/flexibility that Kepler and Lua do.
Is Kepler better than PHP/Java/.Net/...?That depends on what is your goal. Those platforms are surely good solutions for Web Development but sometimes they turn out to be too big, too rigid or just too unportable for the job. That's precisely where Kepler shines.
How small and portable is Kepler?Kepler can be used under very strict memory and CPU scenarios. While every other web platform in the market can use powerful computers, most of them wouldn't even try to fit in a mobile device or custom hardware. Kepler has been used in devices ranging from smart phones to Windows/Linux/OSX big boxes.
What does Kepler offer for the developer?Kepler offers a Core plus a small but powerful combination of components. You have components for SQL Database access, XML parsing, LDAP, SOAP, XMLRPC, Logging, ZIP manipulation and some others.
What is the Kepler Core?The Kepler Core is the minimum set of components of Kepler:
What is the Kepler Platform?The Kepler Platform includes the Kepler Core plus a defined set of components:
Why separate the Kepler Core from the Kepler Platform?If you don't need all the Kepler Platform components or prefer to add your own components, you can simply get only the Kepler Core as a starting point. But if you choose to develop for the Kepler Platform you can benefit from some important points:
Do I need to use the Kepler Platform to use the Kepler Project components?Not at all! The components developed by the Kepler Project can be used in any Lua 5.0 based system. You can compile them from the source files or use the binary versions, both available free of charge on LuaForge.
What about the licensing and pricing models?Kepler and Lua are free software: they can be used for both academic and commercial purposes at absolutely no cost. There are no royalties or GNU-like "copyleft" restrictions. Kepler and Lua qualifies as Open Source software. Their licenses are compatible with GPL. Kepler is not in the public domain and the Kepler Project keeps its copyright.
What is CGILua?CGILua is the main component of the Kepler Core. It is a tool for creating dynamic Web pages and manipulating input data from Web forms. Among other functions, CGILua is the component responsible for the user interface programming side of your Web application, while the remaining ones handle the logic and data of your Web application.
One of the big advantages of CGILua is its abstraction of the underlying Web server. You can develop a CGILua application for one Web server and run it on any other Web server that supports CGILua.
Do I have to use Kepler to use CGILua?No, although it is probably a lot easier to get Kepler and simply start using CGILua than to get CGILua's source and build a launcher for it from scratch. You may also benefit from the fact that Kepler includes lot of ready to use CGILua launchers so you have more choices of Web servers.
What are CGILua launchers?A CGILua launcher is the mechanism that allows a Web server to execute and communicate with CGILua and its Web applications.
Which CGILua launchers are available?Kepler currently offers the following set of CGILua launchers:
You can choose your launcher based on its size, ease of use, portability or performance. You can start using a simpler launcher and then migrate to a more advanced one without any changes to your application.
With this flexibility you can for example start your development locally on your Windows system running CGI and then move to a Linux server running mod_lua or even to a mobile device running Xavante.
What if my Web server is not supported?If your target Web server does not offer any of the existent connection methods or if you would prefer to use a different connection method, you have the option of creating a CGILua launcher for the target Web server.
How can I create a new CGILua launcher?A CGILua launcher implements SAPI, the Server API. SAPI consists in a set of functions that once implemented for a specific Web server architecture allows the execution of CGILua and its Web applications on it.
How ready to use is Kepler?Kepler development is an ongoing process, and you can check the latest release at the Download page. You can also check the status page for the incoming releases.
Who is already using Kepler?Kepler is already being used by PUC-Rio and Hands on real applications.
Is there a mailing list for Kepler?Kepler questions can be posted on the Lua list for now.
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