Model-Based Development (Joanne Romanovich's Library) by H. S. Lahman

Author:H. S. Lahman
Language: eng
Format: epub
Publisher: Addison-Wesley
Published: 2011-06-13T16:00:00+00:00

An alternative way of dealing with the problem is through an ADT that combines Coordinate1 and Coordinate2 into a scalar by raising the level of abstraction. Then Position becomes the ADT and it is magically transformed from a first class object into an attribute. There is nothing to prevent us from then providing a descriptor with a type to indicate polar versus cartesian that can be used in manipulations. That’s fair as long as we can manipulate Position without knowing its elements.

This is usually the preferred solution, and it is worth some effort to see if we can’t abstract the clients of the coordinates so that they only need the abstract Location perspective. In effect, we are refining the level of abstraction of the subsystem in this particular context so that Location becomes logically indivisible within the subsystem.

2NF. All knowledge attributes depend on the full object identity.

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