This is sure not an academic exercise.
We MUST design an Open Source Prototype for this and present it to the potential customer (Government of India?). The complete system should be practical and economically viable.
I think we need to figure out what this can be used for, before we get into other details.
I can think of 2 use cases for such system 1) social or business networking (orkut, linked in types).. a more casual usage
in this case, you probably want to keep its contect voluntary and open.. (ie members can put in whatever they want) If I can get your hotmail password or something else based on getting the answer to your secret question (mothers maiden name, date of birth, pets name).. it is your problem.
2) a system used by government .. ie legally binding.. ( in future, maybe other services like credit rating agencies, organizations trying to verify your identiry?).. this is more formal.. its content are deemed to be reliable by everyone.. it could be used by police across the country to track criminals..
in this case, you may keep a read-only access to the publicly avaialable info.. maybe more access to some paid subscribers (potential customers would be someone issuing a credit card, home loan, or a car loan to you and hence trying to do an identity check/credit or criminal history check on you)
unique id for a citizen? well.. we dont have any unique ID so far.. US has a social security #, UK has a national Insurance #... maybe this is the major benefit of having such a system in the first place - as it can be a single identity for people having (or not having) various diverse id's .. (passport#, DL#, voter id# (for 18+), PAN# (for the few tax payers)).. why not have some biometric ID to make it really foolproof..
u can confidently say that ram ral, s/o shyam lal, living in pin code 100 020 (and with the given biometric ID details) has id 100 and has no criminal records or bad credit history.. so it is safe to lend money to him.. whereas ram lal s/o manmohan singh has defaulted on that previous loan paid to him.. in fact his current address is tihar jail..
but, then you can only design a technical framework to hold this data, and access/amend it. implementation details such as who enters and keeps on updating data would depend on sarkari babus sitting in the villages who are normally happier to exploit and harass the citizens than in serving them.