• An abstract type is defined as an abstract record containing a set of basis variables.

• Generic procedures are written in terms of the basis variables.

• A view type emulates the abstract record using the concrete record as storage:
  • storage property: after a value is stored into a basis variable, a read of the basis variable returns the same value.

  • independence property: storing into one basis variable does not change the values of others.

• A store into a basis variable may require updating several concrete fields.

• Slight inaccuracy in emulation may be allowed (e.g., floating point round-off error in representing (x, y) using (r, &theta)).

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