Grading subjective answers using a program

An Optical Marker Sheet can be scanned and computer readers can detected the shaded spots and detect a correct / wrong answer based on an answer key.

But consider this challenge:-

a) A student can write an exam on a paper => Which can be graded by a computer.

b) A student can type an exam on a computer => which can be graded by a computer.

So, is this solution a) or b) possible ? At least for the option b) I am just wondering what would the software architecture of the system be like ?

Some professors are already using such software : Here is one such software - SA grader from Idea Works.

Just wondering what could be the applications for such a program : subjective grading - checking against a template and evaluating. There must be a "semantic component" in this software which "understands" the text - Just wondering whether it could be used in web search (for longer queries) ?

Reference article : http://chronicle.com/article/To-Justify-Every-A-Some/128528/