Most databases containing personal information are secure to ensure privacy. The Data Protection Act lays out rules that must be followed when holding personal data. There are therefore very few Public service databases containing personal information accessible on the internet. One exception being missing persons as shown at 3 below.
The links below however will give you a good idea of the capabilities of databases when it comes to searching quickly through large volumes of data and they use very similar software to that which runs databases in the Police, NHS, and Military etc.
1.Commonwealth War Graves Commission
This is a huge database giving details of every Commonwealth soldier who died in World War 1 or 2 and who are buried in a war grave, anywhere, throughout the world. There are huge numbers of people listed and the search can be made using several different search fields or any combination of them.
Try typing in your surname and you may well find details of a fallen relative.
2.Federal Bureau of Investigation
The United States have different rules regarding disclosure of information as you can see on this site, which lists all persons currently wanted by the FBI. Click on any of the Photographs for full database information about the individual and the crimes they have committed.
3.Greater Manchester Police – Missing Persons
One of the exceptions to the rule about disclosure of personal information in the U.K. , but permission will have been sought from relatives before making it available to the public.