Instead, they may offer only a limited number of points, normally the midpoints of
edges and/or corners of the enclosing rectangle of the symbol. All roles must connect
to one of these prede?¬?ned points, with less readable and esthetic results. The limited
range of connection points also forces symbol designers to make sure those points are
on the boundary of the symbol, otherwise role lines will stop somewhere in empty
space before the symbol, for example, a horizontal line to the middle of an hourglass
shape.
Rather than allowing a few ?¬?xed connection points, a tool should allow the user to
specify a connection boundary around a symbol, at which incoming role lines will
stop. In the simplest of cases, where a symbol consists of a single graphical element,
that element is itself the connection boundary. Once there are more elements, de?¬?ning
a connection boundary becomes something best left to the metamodeler, although
reasonable defaults should be provided. The boundary will generally be a polygon that
follows the outline of the outermost edges of symbol elements. Incoming role lines
will calculate the intersection point with the ?¬?rst edge of the polygon that they meet,
and stop there.
More complicated cases occur where a symbol contains explicit ports, represented
by visible nodes on the boundary of the symbol.
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