Understanding null references
A null reference in a package is a reference that has no physical content. Its can either be used to trigger a process without content, or to be a placeholder for the configuration data. Being a placeholder for the configuration data enables you to put different types of configuration settings on a single reference, and then have that reference "deploy" to different channels in an environment, with the channel-specific configurations applied to the different servers. You could put all of the configuration settings for a deployment on a single null reference to make them easier to manage, and then have the reference trigger a process to apply the configuration for all channel types.
Null references in BMC VaraLogix Q Deployment Automation perform a variety of functions. Those functions are grouped around two main activities:
Process trigger
In many cases, a deployment requires a certain process to be run with no content inside it. For example, you may need to run a process with no content in order to restart a database, create directories, start an application server, etc. Without the content, BMC VaraLogix Q Deployment Automation cannot invoke that process. To that end, null reference allows you to create a references which will not pull any data during the instance creation. This enables you to create a trigger in a processes which will trigger on the reference name or uri of that null reference. Therefore, if you need to do something during a deployment, but you do not want to do it as part of a file deploy, you can use a null reference.
Configuration management
Normally, references contain application data that is deployed to a specific channel. An executable file might go to an Internet Information Services (IIS) server, while a SQL file might go to a database server. Each reference can have configuration settings associated with it, which will be applied based on the action type for the channel. However, in some cases, you might want to perform configuration actions without deploying any actual data. For example, you might want to configure a load balancer on a separate server from the web application that you just deployed. The system must be able to find a deployment process that matches the target server type.
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