Graphical languages

The two graph-based PLC languages of IEC 61131-3:

Ladder Diagram (LD)

Relay-ladder notation: rungs of contacts and coils between two power rails. Closest match to traditional electrical schematics and the on-ramp for electricians who are new to programming. The ForgeIEC editor exposes LD via a graph editor; the persisted form is PLCopen XML. (Stub.)

Function Block Diagram (FBD)

Boxes-and-wires notation: function blocks are blocks, signals are wires. Closest match to control-loop diagrams. Editor exposes FBD via the same graph editor as LD; persistence is PLCopen XML. (Stub.)