Scoping and Updating Policies
You can create information management policies at two scope levels:
As a site policy, at the level of the site collection Site policies reside in the policy collection at the site collection level. An administrator can choose to make the site policy available within a given site collection. When you assign a site policy to a specific content type or list, a copy of the policy, named a policy instance, is copied locally into the content type or list.
As part of a specific content type or list A policy created within a content type or list applies only to that content type or list. However, you can later export the policy as an XML document and add it to a policy collection or to another content type or list.
Policy instances (that is, policies that are assigned to a specific content type and copied locally) inherit a relationship to the site policy on which they are based. Changes you make to the site policy in the policy collection are propagated to the various instances of that template.
Items on the list to which the policy is applied are updated by means of a daily, asynchronous timer service job. As a result, those items may not be processed and updated immediately. This is also true when you edit a local copy of a policy.
If you assign a site policy to a given content type, you cannot make changes to the policy at the content type level. For example, you cannot assign a site policy to a content type and then customize the policy in that content type to include additional policy features.
However, you can export the site policy as an XML file, and then import the XML file into a content type. This does not establish a relationship between the site policy and content type policy. You can make changes to the content type policy, but any changes you make to the site policy cannot be "pushed down" to the content type policy.
You can derive a policy from another policy in two ways:
You can assign a site policy from the policy collection to a specific content type or list.
You can create one content type based on another content type.
When you create a content type that is based on an existing content type, all aspects of the derived content type are copied from the existing content type, including the policy applied to the initial content type. A new policy instance is copied locally into the derived content type.
If you make changes to the policy instance in the initial, "parent" content type, Office SharePoint Server 2007 updates the derived policies to include these changes. However, you cannot make changes directly to the policy in the child content type.