A logical view of entities and interaction

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1. An entity is composed of a set of internal parts, accessible only within the entity, and an external skin that presents faces(s) to the outside world
2. A part is a set of data and/or functions
3. A skin can have 1 or more faces
4. A face provides visibility to a set of data and/or function contained within
5. A face can either be public (only 0 or 1 allowed), or private
6. A public face is available to all without restriction. A private face imposes a restriction on who can see it
7. A part is uniquely defined within an entity
8. A part can be used in multiple entities
9. A function is a single code element that has a set of input data and a set of output data
10. A function is self contained
11. All data and functions have names that are unique within their part
12. All names must be fully descriptive