Node absorption removes a node without affecting the overall global relationship of the rest of the nodes (i.e. the joint probability distribution).
This small demonstration of node absorption will show how
it doesn’t effect the beliefs of the rest of the net. Open "Car_Diagnosis_2"
from the Examples
folder. Compile it with Network
→ Compile,
and notice that the belief is 25.4% that “Spark Quality” is “good”. If
you enter a finding of “dim” for node “Headlights”, the belief changes
to 1.47%. Now select nodes “Main Fuse”, “Battery Age”, “Voltage
at Plug” and “Spark Plugs”, and then click the 
toolbar
button or choose Modify → Absorb Nodes.
The selected nodes will be absorbed, links will be added and removed,
and probability tables adjusted to maintain the global relationship. Now
do Network →
Compile, and observe the belief
is 1.47% that “Spark Quality” is “good” as it was before the absorption.
If you then do Network → Remove Findings,
the belief changes to 25.4%, which is what it was in the old net before
any findings were entered.
Link
reversal changes the direction of a link without affecting
the overall global relationship of the rest of the nodes (i.e. the joint
probability distribution). Select a link and then click the 
toolbar button or choose Modify →
Reverse Links. Netica
may have to add extra links in order to maintain the joint probability
distribution (or it may be able to remove some links).
See also Disconnecting
and Reconnecting Links