What are challenge problems?

I know in challenge problems, answer is tested against few test cases and rejudged after contest. But how the rating system works? In some problems, during contest, some AC solution get 0.000 points, some 0.001 and some 1.000.

How is 0.000 accepted?

How is it converted to points out of 100 at the end?

Are 0.000 point solutions rejected at the end or they will get some points too?

If they secure few points, will they be considered solved or partially solved?

In ACM-ICPC, or in IOI, does challenge level problem come?

Challenge problems are special problems also known as the tie breakers where you have to solve a particular problem.Your program will be accepted if solves the problem correctly within the given time and memory constraints…But how well is your algorithm is judged by the score your solution gets through judge…The marking scheme here is relative,Suppose there is an algorithm used by someone which has scored 1000 points and my algorithm managed to score 20 points(But both are correct),So score of every correct submission will be changed to (individuals_Score)/Best_score_so_far…So the maximum score a solution can get will be 1.000(The best one and it will score 100 points(1.000 * 100).
As far i know challenge problems are not present in IOI format.
And if a solution score 0.000 means it has indeed scored something but it is quite less compares to the best solution…I mean if our score is 1,and best solution score is say 100000,then the score of the former solution will appear as 0.000 while infact it is 0.00001…I hope it clears your doubt.