Principles of Modeling
- First, The choice of what models to create has
a profound influence on how a problem is attacked and how a solution is
shaped.
- Second, Every model may be expressed at
different levels of precision.
- Third, The best models are connected to
reality.
- Fourth,No single model or view is sufficient.
Every nontrivial system is best approached through a small set of nearly
independent models with multiple viewpoints.
Three major elements:
- the UML's basic building blocks
- the rules that dictate
how those building blocks may be put together
- some common mechanisms that
apply throughout the UML
The vocabulary of the UML encompasses three kinds of building blocks:
-
Things
-
Relationships
-
Diagrams
Three kinds of relationships that are most important: dependencies, generalizations, and associations.
- Dependencies are using relationships. For example, pipes depend on the water heater to heat the water they carry.
- Associations are structural relationships among instances. For example, rooms consist of walls and other things; walls themselves may have embedded doors and windows; pipes may pass through walls.
- Generalizations connect generalized classes to more-specialized ones in what is known as subclass/superclass or child/parent relationships. For example, a picture window is a kind of window with very large, fixed panes; a patio window is a kind of window with panes that open side to side.