Arc States

Context

• An arc connects a Parent Node with a Child Node, and it represents a direct probabilistic relationship between those two linked nodes.
• Creating a new arc between nodes (see Arc Creation Mode) generates a new entry in the probability table associated with the Child Node.

Arc States

An arc can be in one of four states:

• Normal: the default state of any arc. It appears as a solid line with an arrowhead.
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• Selected: left-clicking an unselected arc selects it. Then you can perform operations on the arc, such as Delete or Change Orientation (see Arc Context Menu). A Selected arc is highlighted with a thicker line and a bigger arrowhead.
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• Fixed: a fixed arc indicates that prior knowledge is applied to the network structure before learning. The line of a Fixed arc is dotted.
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• Temporal: a Temporal Arc indicates a temporal relationship between a parent node N at time step t, denoted N(t), and a strictly identical child node at time step t+1, denoted N(t+1). A Temporal Arc transforms the network into a dynamic Bayesian network. The parent node in a temporal relationship can only have one temporal child node. A Temporal Arc is shown with a dashed line.
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Arc Appearance

Translucence

In addition to the formal Arc States described above, an arc can appear translucent:

There are several possible reasons for this appearance:

• One or both of the nodes that are connected by the arc are excluded from display because of the Class Filter.
• The arc does not meet the threshold defined in one of the Visual Arc Analysis functions:
  • Arc Force or Kullback-Leibler Divergence
  • Arc Mutual Information
  • Arc Pearson Correlation
• Regardless of the reason, while an arc is translucent, it cannot be selected or otherwise modified.

Highlight

Specific functions can highlight an arc with distinct colors, such as blue and pink:

Among these functions are:

• Influence Path Analysis
• Cycle Introduction Warning

Undirected Arcs

Arcs can appear as undirected in special contexts:

However, the functions that produce this undirected appearance are very different in nature.

• The Display Skeleton function simply removes all arrowheads in the network from display, for instance when explaining a graph to someone who is not familiar with Bayesian networks. In non-causal Bayesian networks, a casual observer may misinterpret a directed arc as a causal relationship. Temporarily removing all arrowheads reduces the risk of a misunderstanding.
• The Equivalence Classes function visualizes the Equivalence Class by displaying the Essential Graph for the given network. If the Essential Graph contains edges, i.e., undirected arcs, they are shown as such.

Icons on Arcs

The information icon attached to the middle of an arc indicates that an Arc Comment is associated with the arc.

If Show Information While Hovering is active, as indicated in the Toolbar by the icon, you will see the Arc Comment when your cursor hovers over the information icon . You can also activate this mode with the I shortcut.