XML Schema Complete Reference, The

12.1. Numeric Datatypes

Datatypes are numeric if their value space consists primarily of real numbers. Of the built-in numeric datatypes, all except two have value spaces containing only numbers. The two exceptions, float and double, have three additional values: POSITIVE INFINITY, NEGATIVE INFINITY, and NOT A NUMBER. (These two datatypes were inspired by IEEE 754, a standard for “floating point” arithmetic.)

Recall that the natural numbers—or nonnegative integers—are all real numbers, the integers are the natural numbers and their negatives, and the rational numbers are those real numbers that can be obtained by dividing one integer by another. As it happens, all the built-in numeric datatypes have data spaces that contain only rational numbers. ...