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The values in a DDL XML document can be overridden in two ways: environment variable substitution and via DDL Override Properties. In both cases, the source of properties for substitution is provided to the parser passed to the VMConfigurer.  When running in Non-Embedded mode, the substitution values provided by the Talon XVM to the the VMConfigurer are sourced from the bootstrap environment which consists of the following sources (in increasing order of precedence):

Bootstrap Environment:

• The application properties file. This file can be specified in the environment as nv_app_propfile, or as a System property as '-Dnv.app.propfile'. A value found in the environment takes higher precedence.
  
• System properties (System.getProperties)
• The host's environment (System.getenv())

When running in embedded mode or with a bootstrap configurer, the application may provides the substitution value resolver to an alternate substitution environment using the VMConfigurer directly via API, giving the application full control of over the bootstrap property source. In this case, the application may provide VMConfigurer with the platform's environment value substitution resolver above bootstrap environment by passing in UtlTailoring.ENV_SUBSTITUTION_RESOLVER as the valueResolverVMConfigurer's valueResolver. 

Environment Variable Substitution

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