Class which represents an abstract extension/encapsulation object. An object, from here on
denoted as original,can be encapsulated in or extended by another object. An example would be the
relation between an edge (original) and an annotated edge. The annotated edge
encapsulates/extends an edge, thereby augmenting it with additional data. In symbolic form, if b
is the original class, then a(b) would be its extension. This concept is similar to java's
extension where one class is derived from (extends) another class (original).