First you need to know that 0 and 1 are fractions themselves !
[math]0 = \frac{0}{1}\quad and\quad 1 = \frac{1}{1}[/math]
Although we don't usually write them like that.
Mathematics recognises a series of 'number systems' that are nested like Russian dolls.
The outer one is the most complicated and the number systems get simpler inside just as the outer doll is the biggest and the dolls get smaller inside.
For number systems the more complicated (outer) system contains or includes all the simpler systems within it.
The simplest system is called the natural numbers or counting numbers. 1,2,3,4,5...... There is no zero in these.
Then we have the positive inetgers if we want the same thing but with a zero 0,1,2,3,4,5......
The we have both positive and negative integers ...-5,-4,-3,-2,-1,0,1,2,3,4,5...... These are all the integers.
The we have the rational numbers : ratios of two integers ie fractions
[math]\frac{1}{2},\frac{{25}}{{39}}etc[/math]
We do not need another category for the ratios of decimal numbers since they can always be written as the ratio of two integers
[math]\frac{{2.5}}{{3.138}}is\;the\;same\;as\frac{{2500}}{{3138}}[/math]
Which is a number system as far as you have asked since it includes all the fractions lying between 0 and 1 that can be written.
And it also answers you question about number bases.
Simply it does not matter which base you choose as shown by the example of rewriting a decimal fraction as the ratio of two integers.
But there are yet more important numbers that cannot be written this way. An example would be the reciprocal of the square root of 2, or the square root of 0.5.
So we come to the what are called the real numbers as corresponding to our outer Russian doll, and includes all these numbers as well as all the fractional ones.
I hope you can see nesting idea from this.
There are yet more complicated layers of 'numbers' but I will leave it at that.