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This section contains detailed reference information for the x-ddl schema (Domain Descriptor Language). An X-DDL You Your application's config.xml is an XML document, adhering to the X-DDL schema, describes and configures a system of buses, applications and XVMs that together constitute a multi-agent 'system' that is managed and deployed together to perform a higher level business function. The DDL document is used to configure each XVM prior to launch and is used by the X Platform's deployment and monitoring tools to assist in managing the system as a whole. 

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• <systemDetails>: Defines system metadata that is used by tools and emitted by an XVM in heartbeats. 
• <env>: Defines environment variables that can be used for substitution of values in the document and are exposed to the application and talon runtimes.
• <busProviders>: Defines custom message bus provider implementations.
• <buses>: Defines the message buses that are used for applications to communicate with one another.
• <apps>: Defines and configures the applications that make up the system. 
• <xvms>: Defines the XVMs (Talon lightweight containers) that host one or more applications. 
• <profiles>: Defines profiles that can be dynamically activated to localize the configuration for different operating environments.

A main tenant tenet of the X Platform is to separate out (and shield) an application's business logic from the complex machinery underpinning high availability, performance, and scalability. As such there is a wealth of tuning knobs and configuration operations that can be applied without making application code changes. Most applications will not use the majority of the settings described here unless they are being tuned for special cases. 

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