Nets and Connections

This model contains the objects visible in the graphical interface that are used to connect icons together.

Additional notes on the model:

• A Vertex is either a Star or another type of Vertex called (for want of a better name) NotStar. A Vertex contains one or more ports indexed by name. Each Port connects to zero or more other Ports, via an Edge. A Vertex can be either a Star or a NotStar, which has a type attribute to give further information about it, such as whether it is a junction, a delay, a bus splitter, and so on. Edges have a single attribute, being the width (zero means an atomic edge).

  The object that translates the graph containing Vertices, Edges, and Ports, will know what to do with NotStars.

• Each Vertex is visually represented by exactly one Iconic object. These objects include icons taken from an IconLibrary, or other objects that have special significance in the visual representation, such as Junctions and (for Ptolemy-style graphs) Delays. If an Iconic object is pinned, then it can be moved explicitly only by selecting and dragging it; if not, it may move if a connected Net moves. Icons are always pinned; Junctions and Delays can have this attribute set by the user.

• Each Edge is visually represented by exactly one Net, which is either a Bus or a Wire. arrowposition controls the position of arrowheads on the net, and is determined by the net-placing code based on terminator.direction. A Wire is shown here as having some Decorations -- the intention here is that certain attributes of an edge may be made visible in the user interface. A Net has zero or more Grapples attached to each vertex, for reshaping and reconnecting the Net. Busses can be connected only to a Connectible object that is composite. In the case of Terminal, this flag is determined by the Star; in the case of Junction, Grapple, and Delay, the flag is derived from other connected Nets.

• A Net connects-to exactly two Connectible objects. This constraint simplifies both the implementation and the user perspective considerably. There is no loss in expressive power because of the way that Junctions and Nets work together. A Connectible object has zero or more connected Nets, determined by the connectivity attribute (I don't know if this is legal OMT/UML, but it works for me...). Terminals and Grapples can have only one Net connected to them, but Junctions (for example) can have up to four.

• The tag and selectivity of a Connectible object determine its interaction with the controller. If an object can be selected, then it can also be moved around with the mouse -- for example, the user can select an Icon or Junction and drag it (and connected Nets) around. An object may highlight when the mouse passed over it if tag and the number of connected nets indicates that additional nets can be connected -- clicking and dragging on it then cause a new edge to be created. The distance that the mouse must move to start a new Net is given by the hysteresis.

• A Grapple can be sticky. Sticky Grapples are attached to the ends of disconnected nets, so that the nets can be easily moved or reconnected. Grapple that are not sticky are created when an edge is selected and disappear when it is deselected.

JohnR, 14 Oct 97