PTOLEMY II - CiteSeerX

MoML
the three entities. They have ports with arrowheads suggesting direction. There is a single relation,
which shows up visually only as a set of lines and two vertices. The vertices are shown as small diamonds.
A vertex is exactly like a property, except that it has an additional attribute, pathTo, used to link
vertices, and it can be referenced in a link element. Like any other property, it has a class attribute,
which specifies the class implementing the vertex. In Ptolemy II, the class for a vertex is typically
ptolemy.moml.Vertex. Like other properties, a vertex can have a value. This value will typically specify
a location for a visual rendition. For example, in Ptolemy II, the first vertex above might be given
as
This indicates that the vertex should be rendered at the location 184.0, 93.0.
Ptolemy II uses ordinary MoML properties to specify other visual aspects of a model. First, an
entity can contain a location property, which is a hint to a visual renderer, as follows:
This suggests to the visual renderer that the Ramp actor should be drawn at location 50.0, 50.0.
Ptolemy II also supports a powerful and extensible mechanism for specifying the visual rendition
of an entity. Consider the following example:
The SingletonAttribute class is used to attach an XML description of the rendition, which in this case
is a wide box filled with green. The XML schema used to define the icon is SVG (scalable vector
graphics), which can be found at http://www.w3.org/TR/SVG/. 9
9. Currently, the Diva graphics infrastructure, which is used by Vergil to render these icons, only supports a small
subset of SVG. Eventually, we hope it will support the full specification.
212 Ptolemy II