Charlie FAQ

Petr Cimprich

A: Would you like to have an open architecture allowing distributing data from any sources to any clients? Would you like this system to be based on industry standards with no proprietary features? Would you like all this to be available for free with source code? So do we. Charlie is an attempt to meet such a need.

A: Charlie contains several third-party components: Expat is released under the Mozilla Public License 1.1 or the GNU General Public License alternatively). Java-Script and the JS perl package are also under the MPL 1.1 (or the GPL alternatively).

The rest of Charlie code has been created by the Ginger Alliance and includes Sablotron and Charlie perl packages. These components are also subject to the MPL/GPL to keep the licensing policy consistent.

A: Yes, Charlie contains two third-party components.

• An important part of Charlie is Sablotron, which contains James Clark's expat XML parser. Expat is subject to the Mozilla Public License or the GNU General Public License alternatively.
• Charlie uses the Mozilla JavaScript engine, which is subject to the Mozilla Public License.

A: Currently, we run Charlie on Linux and Solaris. It is designed to run on Windows as well but we are too focused on its functionality to experiment with other platforms now. Basically, Charlie should run under each platform supporting C/C++ and perl.

A: Yes, it does. Current Charlie implementation contains no http server, so that it must be installed before Charlie can run. Charlie uses its cgi (or mod_perl) interface. The http server configuration has to include some Charlie stuff; see Charlie INSTALL file for more details. We have tested only Apache (1.3.9) and mod_perl (1.21) so far but any http server should work.

Charlie also requires perl and some perl modules to be installed. We try to keep the number of external modules as small as possible; the complete list will be published within the Charlie documentation.

A: If you want Charlie to do something (well, the only thing Charlie can do is to give you an XML document), you have to pass it a URL. Each URL points (explicitly or implicitly) to a so-called action. The action describes how to create the XML document to be returned. The common way would be to get an XSLT template and source XML data, transform the source according the template and return the result. Each input can be either local file, remote file downloaded via http, or output from any local/remote program. The output of the action depends on the XSLT template, which should depend on the client who is running the action. You may wish your data in HTML, WML or other DTD.

Charlie is a layer between the client and the server/data provider. You can think of it as a kind of proxy if you wish. It can be located on the same machine as the client, on its own machine, or by the server. Each of these possibilities makes sense. You can employ Charlie as a local cache that is able to work off-line (to some extent), as a LAN proxy, or as a server XML interface.

A: No, it is not. The language for writing actions is JavaScript. Though you can employ all features of this language, a common action uses only few Charlie specific objects and methods. A simple action can for example look like this:

	  // getting XSLT template
	  templ = charlie.getDocument(xsl_template_url);
	  // geting XML data
	  data  = charlie.getDocument(xml_data_url);
	  // processing template and data
	  ret   = processXSLTStrings(templ,data);
	  // creating body of response
	  response.document(ret);
	  // creating http header of response
	  response.contentType("text/html");
	  // return code
	  1;
	

The six-line action is able to provide the data, process them and send them back to a client using the http protocol. On the other hand, JavaScript is a full-featured programming language, which provides you with all you need. Charlie action allows you to do simple things simply and complicated things the way you want.

A: Sure. Although Charlie can offer much more, you can use it to transform any existing XML data to HTML. All you need is to install Charlie, write down a few simple actions and create XSLT templates.