aiSee: Edge Format

Edge format

There are several different kinds of edges: ordinary edges, back edges, near edges and bent near edges. An ordinary edge is specified by

edge: { source: "title"
        target: "title"
        list of edge attributes }

There are two kinds of graph elements that can (and must) have titles: nodes and subgraphs. In other words, this means that an edge can link:

A node to a node,
A node to a subgraph,
A subgraph to a node,
A subgraph to a subgraph.

Special kinds of edges

Back edges are drawn in the opposite direction as compared to ordinary edges. For instance, if the layout algorithm tries to give all ordinary edges a top-down orientation, it tries to give the back edges a bottom-up orientation. If a graph contains a cycle and some edges have thus to be reversed, the layout algorithm prefers back edges before selecting any other edge to be reversed (see example). A back edge is specified by

backedge: { source: "title"
            target: "title"
            list of edge attributes }

Near edges are drawn so that their source and target nodes are directly neighbored at the same level. This implies that a node cannot have more than two near edges, i.e. one on the left and one on the right with respect to the orientation of the graph. Near edges are drawn as short horizontal lines not crossed by any other edges or nodes. Invisible near edges can be used to group nodes at one level. A node can only have two near edges. If more than two near edges are specified for a node, the remaining near edges are converted into normal edges. A near edge is specified by

nearedge: { source: "title"
            target: "title"
            list of edge attributes }

GDL also allows the target node to be placed directly neighbored to the left/right of the source node at the same level:

leftnearedge:  { source: "title"
                 target: "title"
                 list of edge attributes }

rightnearedge: { source: "title"
                 target: "title"
                 list of edge attributes }

Bent near edges consist of a horizontal part (same as near edges), a bend point and a vertical part. An edge label (if any) is placed only at the bend point. So bent near edges connect nodes across one or more levels yet leave the source node at the left or right side. A near edge is specified by

bentnearedge: { source: "title"
                target: "title"
                list of edge attributes }

GDL also allows specifying whether the horizontal part of the edge should leave the source node on the left or the right side:

leftbentnearedge:  { source: "title"
                     target: "title"
                     list of edge attributes }

rightbentnearedge: { source: "title"
                     target: "title"
                     list of edge attributes }

» Next: Attribute format
» Prev.: Graph and node format

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