The robust principles of port-based engineering known to disciplines such as electrical engineering, mechatronics, and systems engineering are now finding practical expression in graphical software engineering through aspects of UML2 including:
- The StructuredClassifier: which enables the recursive composition of wholes in terms of its part Properties.
- The EncapsulatedClassifier: which enables the isolation of the services and behaviors of a Classifier via Ports which provide and require Interfaces:
- The Connector: which enables the assembly of parts within a StructuredClassifier, and the delegation from/to Ports at the boundary of EncapsulatedClassifiers to/from internal part Properties and Ports of parts. A Connector may also carry an InformationFlow.
- The Class and Component are also StructuredClassifiers and EncapsulatedClassifiers.
UML2 Classes and Components are thus Holons. From http://en.wikipedia.org/wiki/Holon_(philosophy):
'A holon is a system (or phenomenon) that is a whole in itself as well as a part of a larger system. It can be conceived as systems nested within each other. Every system can be considered a holon, from a subatomic particle to the universe as a whole. On a non-physical level, words, ideas, sounds, emotions—everything that can be identified—is simultaneously part of something, and can be viewed as having parts of its own, similar to sign in regard of semiotics.Since a holon is embedded in larger wholes, it is influenced by and influences these larger wholes. And since a holon also contains subsystems, or parts, it is similarly influenced by and influences these parts. Information flows bidirectionally between smaller and larger systems as well as rhizomatic contagion. When this bidirectionality of information flow and understanding of role is compromised, for whatever reason, the system begins to break down: wholes no longer recognize their dependence on their subsidiary parts, and parts no longer recognize the organizing authority of the wholes. Cancer may be understood as such a breakdown in the biological realm.
A hierarchy of holons is called a holarchy. The holarchic model can be seen as an attempt to modify and modernise perceptions of natural hierarchy.'.
Through progressive encapsulation of functionality as EncapsulatedClassifiers with declaration of provided and required services as Interfaces, UML2 Classes and Components promise to enable greatly improved development and testing of increasingly complex, reusable software components.
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