Calculated question type creation

Its a first try as you could see. I will use this page to describe the PHP code principal processes of the calculated question creation and see how it could be improved.

Calculated question parameters

Calculated question is an extended numerical question where parameters of a mathematical problems are generated and used to calculate the answer using a mathematical formula.

So the answer parameter of a numerical question is replaced by the mathematical formula using the same answer database structure that the numerical question.

The generated parameters are identified by a special format that is not used in a mathematical PHP equation {param} where the param name begins by a letter and can include alphanumerics symbol a-z A-Z _ 0-9

ex. {ad} {a_2} {a4_r} are valid parameter names 
{1a} {a+1} {a(0)} are invalid parameter names
 

These parameters are transform in datasets defined by a min,max,decimal and generation mode. Using these datasets definitions a number of different values are generated (the dataset items) and used to generate different question instances where the parameters have different values although the question structure and answer formula are constant.

Actually the creation of a calculated question is a three step process

1. Defining the common question parameters
   1. Question name
   2. Question text
   3. answer formula, limit, units
2. Defining if the dataset definitions ({params} are to be used in this question only or could be used by other questions in the question category in which the question is created.

 question category is a set of questions that can contain various question types