The XML registry

We discussed many of the fundamental components of the FreeSWITCH core and how they interact with each other. We have seen how the event system can carry information across the core to the modules, and how the XML Dialplan can query the XML registry for data. This would be a good time to explain the XML registry a bit more. The XML registry is the XML tree document that holds all of the critical data that FreeSWITCH needs to operate properly. FreeSWITCH builds that document by loading a file from your hard drive and passing it to its own pre-processor. This pre-processor can include other XML documents and execute other special operations, such as setting global variables. Global variables will then be resolved by FreeSWITCH when they're used further down in the document tree.

Once the entire document and all of the included files are parsed, replaced, and generated in a static XML document, this final static document (with all global variables substituted for) is loaded into memory. The XML registry (tree) is divided into several sections- configuration, dialplan, directory, chat plan, languages, phrases, etc. The core and the modules draw their configuration from the configuration section. The XML Dialplan module draws its Dialplan data from the dialplan section. SIP and Verto authentication, user lookup, and the voicemail module read their account information from the directory section. The Phrase Macros pull their configuration from the phrases section. If we make a change to any of the XML files on the disk, we can reload the changes into memory by issuing the reloadxml command from the CLI If we change the values assigned to one of the global variables, we will need to restart FreeSWITCH to apply the new value, reloadxml will not be enough.