Shared Property variables can be defined and passed into an update from the host application as an update is being applied. A collection of shared properties can be passed as a parameter to the methods that launch an update from the host application. Some update actions can also set shared properties.
The actions that allow update designers to set shared property variables that can be used in other actions through expansion are:
Transacted Database Stored Procedure
Shared properties can also be set within Dynamic Actions and custom actions. These actions can directly manipulate the Shared Properties collection by using the Update Context object available within the method parameters. This information can then be shared with other update actions by placing expansion variables.