Resumen
Despite the fact that languages and products supporting some kind of type inheritance already exist. The basic idea of inheritance is quite simple, its central role in current object systems, inheritance is still quite a controversial mechanism, comprehensive view of inheritance is still missing. There are at least four types of inheritance: substitution inheritance, inclusion inheritance, constraint inheritance and specialization inheritance. Comprehensive inheritance model supports both single and full multiple inheritance. It recognizes the fact that a rectangle with equal sides is actually a square. The model integrates well with, and abides by the principles embodied in the relational model of data. What's more, it involves no changes or extensions to the relational model. It was observed that by definition, a value cannot be updated; for if it could, then after such an update it would not be the same value any longer. Variables, by contrast, can be updated; the current value of the variable in question can be replaced by another value, different from the previous one. And so the distinction between value and variable leads to another crucial distinction, that is, between read-only and update operators.