To create a new Arc type, simply drag the Arc Type shape from the toolbox onto the canvas and enter the name and identifier for the new Arc Type. Unlike associations, arcs have a specific direction - a topic type can be used at the start or end of an arc (or both, but each needs to be specified separately).
Schema Editor showing an Arc Type
To specify that a Topic Type can be used at the start of the arc drag a line from the Topic Type to the Arc Type. You will then be prompted to enter the cardinality constraints that specify how many times an instance of the Topic Type can appear at the start of an arc of the Arc Type. The default of 0..* is the most commonly used constraint. The line will display as an arrow pointing from the Topic Type to the Arc Type.
To specify that a Topic Type can be used at the end of the arc, drag a line from the Arc Type to the Topic Type. You will be prompted to enter the cardinality constraints that specify how many times an instance of the Topic Type can appear at the end of an arc of the Arc Type. The line will display as an arrow pointing from the Arc Type to the Topic Type.
Arc Type with constraints added
NOTE: It is possible to add multiple Topic Types at the start or end of an arc, this simply means that the topic map creator can use any of the specified types at the start or end of the arc. It is also possible to use the same Topic Type for both the start and end of the Arc Type (e.g. Person -> knows -> Person)