Creating and Using Net Libraries
Creating: Netica makes it
easy to maintain libraries
of disconnected
nodes and subnets. To make a new library, just choose File
→ New
→ Network
or click the 
toolbar button. Libraries are
handled internally in the same way as regular nets. Nodes and subnets
can be copied to it by = 4 && typeof(BSPSPopupOnMouseOver) == 'function') BSPSPopupOnMouseOver(event);" class="BSSCPopup" onclick="BSSCPopup('X_PU_select_node.htm');return false;">selecting nodes (there is no need to select
links), and using Edit →
Copy and Edit
→ Paste,
which can transfer material (nodes, links and = 4 && typeof(BSPSPopupOnMouseOver) == 'function') BSPSPopupOnMouseOver(event);" class="BSSCPopup" onclick="BSSCPopup('X_PU_CPT.htm');return false;">CPTs) from one net to another. When
a node is being duplicated, but one of its parents isn’t, then the duplicated
node will have a disconnected link where that parent was.
Using: To use nodes in the library, you use Edit → Copy and Edit → Paste again, this time to duplicate from the library into the new net. Then you connect up any disconnected links, before compiling the net or using it for inference.
Example: For example, to create a library with just the “instrument” node of figure 6.1, first you would make a net with the 4 nodes: flow_rate, temperature, instrument_status and instrument. Put links from nodes flow, temperature and instrument_status to instrument. Enter a probability table for the node “instrument”. Now make a new net with File → New → Network, select the “instrument” node in the original net, do an Edit → Copy, click in the new net, do an Edit → Paste, then a File → Save. You now have file which is a library with a single node in it.
At a later session, you can use the library to construct a net in which the instrument is used to measure the flows as described at the beginning of this chapter. Make a new net with File → New → Network, add the nodes flow1, flow2, instrument_status and room_temp, link them together as shown in figure 6.2, and enter the probability table between them. Then use File → Open to open the library file with the instrument node. Select that node, do an Edit → Copy, then click in the application net where you want the instrument node to appear. Do an Edit → Paste, click again where the other copy of it should be and do another Edit → Paste. Finally, hook up each of instrument’s disconnected links to their appropriate nodes using the method described in the previous section.
Now the application net is ready for probabilistic inference (you can do a Network → Compile menu command). Perhaps you have positive findings for the “instrument” node (i.e. what you read from its dial), and you use them to determine flows and their uncertainties in a way that properly accounts for random (uncorrelated) and systematic (correlated) errors, as well as all the background knowledge about the situation.
Netica API: As a sister product,
= 4 && typeof(BSPSPopupOnMouseOver) == 'function') BSPSPopupOnMouseOver(event);" class="BSSCPopup" onclick="BSSCPopup('X_PU_Netica_API.htm');return false;">Netica Programmer’s Library
(API) can be useful for automating the process of constructing nets that
are composed of nodes or subnets from a library, perhaps by using templates
or rules.