It is a toy example; or more accurately, a "thought experiment". However, I suppose the CIA/FBI might have something like it to track suspicious people, such as John Lennon. It would be a huge database of info about people. I imagine most of such a system would either be ad-hoc querying and alert reports that signal suspicious behavior based on some score-giving algorithms. I suspect the schema would look something like:

Table: People
-------------
PersonID
SSN
FirstName
Middle
Last
BirthDate
HairColor
ImageURL
FatherRef (foriegn key to People)
MotherRef
....

Table: LivedLocations
-----------
liveLocID
personRef
LocType (Apt, house, etc.)
AddressRef (ref to location table)
....
FromDate
ToDate
....

Table: WorkedAt
----------
....

Table: countriesVisited
--------------
....

Table: suspiciousEncounters
--------------
personRef1
personRef2
AddressRef
spottedBy
se_notes
.....

(However, because multiple people can meet, perhaps we need a Meeting table, and then a many-to-many table for each person at the meeting.)