Shirako actors must exchange context-specific information to guide the policies and configuration actions. For example, a guest expresses the resources requested for a ticket, and it may have specific requirements for configuring those resources at the site. It is difficult to maintain a clean decoupling, because this resource-specific or guest-specific information passes through the core.
Shirako represents all such context-specific information in property lists attached as attributes in requests, tickets, and leases. The property lists are sets of (key, value) string pairs that are opaque to the core; their meaning is a convention among the plugins. Property sets flow from one actor to another and through the plugins on each of the steps and protocol exchanges depicted in Figure 2.