You have to answer the following questions (in spanish).

A. Write the following described types into XML Schema. For every question, you can use the types you defined before.
   
1) An integer between 1 and 10
2) A list of integers
3) A list composed of either integers between 1 and 10 or a string that can be "a", "b" or "c"
4) An element that contains one attribute "id" which is an integer between 1 and 10
5) An element that contains a sequence of elements "a" (0 or more) followed by a sequence of elements "b" (0 or more)
6) A type (named X) that is composed of an element "name" (containing a string) and zero or more  elements "composed-of" which contain elements of type X and of name "element".


B. What is the principle of key references in XML schema? What are the involved XML schema instructions and what is their purpose?

C. What is the difference between a complex type and a simple type?

D. When should I use a anonymous type instead of a named type?

E. What are the differences (cite one concept that exists only in each of theses schema languages) between XML schema and (choose one and only one). :
   - schematron
   - RelaxNG
   - DTD