Editing Rete algorithm (section)

=== Alpha network ===
The "left" (''alpha'') side of the node graph forms a discrimination network responsible for selecting individual WMEs based on simple conditional tests that match WME attributes against constant values.  Nodes in the discrimination network may also perform tests that compare two or more attributes of the same WME.  If a WME is successfully matched against the conditions represented by one node, it is passed to the next node.   In most engines, the immediate child nodes of the root node are used to test the entity identifier or fact type of each WME.   Hence, all the WMEs that represent the same [[wikt:entity|entity]] type typically traverse a given branch of nodes in the discrimination network.

Within the discrimination network, each branch of alpha nodes (also called 1-input nodes) terminates at a memory, called an ''alpha memory''. These memories store collections of WMEs that match each condition in each node in a given node branch.   WMEs that fail to match at least one condition in a branch are not materialised within the corresponding alpha memory.   Alpha node branches may fork in order to minimise condition redundancy.