Start up Jinx by simply typing jinx. When you don't have a Jinx database ready, make one with Guess. Try file /etc/passwd with separator `:'. Write the database to disk with Save as as blob. Update the descriptor with Descr. Change the names into something meaningful. Now, make two new databases hidden and rest consisting of the (login,passwd) columns and of the (login,uid,gid,name,home,shell) columns. If you succeed, try to Join them again and save the result as blib. Diff blob.dat and blib.dat. They should be the same.
Now, suppose a computer science department has a secretary where students
go when they come to study.
Every student has a student-card with a unique number on it.
The secretary keeps an address database mapping card-ids to info about
the bearer like name, address, etc.
Suppose a teacher wants to keep a record of every student following
some course.
The teacher can open the address database and extract the relevant records,
project out the irrelevant fields, add some new fields, and save it as the
course database.
If a student comes to enroll later, the teacher can Read in the
address database again to add the student's record to the course database.