Matching unique ids in two different databases

I have two different databases that are not connected in any way. In fact, one is a public school database and one is a hud (housing) database. By law they are not allowed to share names and other specific identifying addresses. Birthdates and addresses are okay - along with zip codes and other more general ids. The uses need to be able to query the other database to get non-specific information so it would appear that they need to share the same unique id. I was considering such things as using birthdates and perhaps initials of name or perhaps last 4 digits of ssn along with the birthdate. The client was thinking of global positioning data but I'm concerned about apartments next to one another or movi开发者_运维百科ng of families. Any ideas?

First you need to determine what will be your measure of uniqueness. If there are two people in either database with more than one entry for your measure of uniqueness, you need to change your strategy. After that, put a constraint on both databases constraining that these properties(Birthday, SSN) are what make a Person record unique.