Attribute is the super abstract class that is extended by both the InputAttribute and OutputAttribute.
This class encapsulates the basic fields of an attribute, and provide the get/set methods. Attribute(s) are used in the state implementation to represent input and output attributes.
In addition, Attribute holds the state processing context that is used, for example, to access or store the attribute value as a session variable in the datasource so that it is durable across session. The state processing context is assigned to the attribute by the processing engine during initialization of the state using the setContext(SmappStateProcessingContext) method. Hence, this method is reserved to be used only by the processing engine.
NOTE: Attributes that are used in the same states must have unique ids.