Each node in the Graph View is marked by one or more node status icons. These are tiny icons displayed in the lower right corner of the node icon. There are six different node status icons: Observed, Implied, Controlled, Target, Valid, and Invalid. We will explain their meaning on simple examples.
Observed Status Icon
The Observed status icon (
) is displayed when the user enters evidence into a node and it signifies that the node is an evidence node. Node Expert forecast in the following model is an evidence node and is marked with the Observed status icon:
Implied Status Icon
Sometimes, observing a node implies the values of other nodes. For example, observing that a patient is biologically male in a medical decision support system will imply that he is not pregnant. This is possible because the program realizes that for a male patient pregnancy is impossible. GeNIe marks the nodes whose values are implied by observations of other nodes by the Implied status icon (
). The Implied status icon is identical to the Observed status icon, but it is yellow in color. In the following example, the Gender of the patient has been observed to be Male and the value of the Pregnancy variable has been determined by GeNIe to be False.
Controlled Status Icon
Controlling the value of a node is different from observing it (see Changes in structure section). When a node is controlled, GeNIe marks it with the Controlled status icon (
). Node Communications in the model below has been manipulated and marked as Controlled.
Target Status Icon
The Target status icon (
) has to do with GeNIe's support for relevance reasoning. Very often in a decision support system, only a small number of variables are of interest to the user. When the model used by the system is large, the amount of computation to update all variables may be prohibitive while being in a large part useless. GeNIe allows to designate those variables that are of interest to the user as targets. Target nodes are always guaranteed to be updated by the program during its updating procedure. Other nodes, i.e., nodes that are not designated as targets, may be updated or not, depending on the internals of the algorithm used, but are not guaranteed to be updated. When no nodes are designated as targets, GeNIe assumes that all variables in the model are of interest to the user, i.e., all of them are targets. The node Success of the venture has been marked as Target in the following model:
Valid Status Icon
The Valid status icon (
) marks those nodes that have been updated and have their values available for examination. Valid status icon can appear together with the Target mark, but never with the Observed and Implied marks (note that when a node is observed, its value is known). To make the value valid, simply update the model. Both variables in the following model are marked by the Valid status icon, which means that their marginal probability distributions are available and ready for examination:
Invalid Status Icon
The Invalid status icon (
) marks those nodes that need updating, i.e., their values (or the probability distributions) are invalid and cannot be inquired. Invalid mark can appear together with the Target mark, but never with the Observed and Implied marks (note that when a node is observed, its value is known). To make the value valid, which will make the Invalid icon disappear, simply update the model. Both variables in the following model are marked by the Invalid status icon, which means that their marginal probability distributions need recomputing:
