2. Adding new rules

Next, we create the rule which gives the chance of "Live-Steam" during an accident. Recall that we assigned this event the probability .01. Because we are always implicitly conditioning on an accident, this is represented by an unconditional probability mass function (PMF) in the graphical model. Looking at the rule templates on the right hand side of Figure 3, we see that the PMF rule is already there. So we drag the pmf rule into the window to create a new PMF rule and we name it "Steam-Rule". Figure 4 shows a detailed view of the result.

Figure 4. Model after creating "Steam-Rule" variable. Round boxes on the side of rule node are handles for connection to variables.

Because "Steam-Rule" is an unconditional rule it has no input handles, just a single output handle. We drag the output handle over the "Live-Steam" variable to connect them. Note also that the icon for the "Steam-Rule" has a question mark on it. This is because we haven't yet defined its valuation (in this case probability table). We do that next.

Figure 5. Valuation editor for "Steam-Rule".

Figure 5 shows the valuation editor for the steam rule. We fill in the probabilities in the appropriate boxes and save it. The icon on the "Steam-Rule" changes from the red undefined table to the blue defined table icon. We no longer need the rules "Ma" and "Mb" which defined the failure rates for the motor operated valves so we remove them by dragging them on top of the "green eater" in the corner of the screen. Next, we create the new class of rules to replace them.

Continue with this example and create a new class of rules which describes the distribution of MOV failures conditioned on the presence of live steam.

Model Construction. Go back to the begining of this example.

Return to the main example page.

Back to overview of Graphical-Belief.

View a list of Graphical-Belief in publications and downloadable technical reports.

The Graphical-Belief user interface is implemented in Garnet.

Get more information about obtaining Graphical-Belief (and why it is not generally available).

get the home page for Russell Almond , author of Graphical-Belief.

Click here to get to the home page for Insightful (the company that StatSci has eventually evolved into).

Russell Almond, <lastname> (at) acm.org
Last modified: Fri Aug 16 18:44:01 1996