Proper use of TDBF.Lookup

[AlZuur]

How should I properly use TDBf.LookUp?

in the following:
  PersonId := Sender.AsInteger;
  PersonName := PersonDbf.Lookup('id', PersonId, 'firstname;lastname');
  aText := PersonName[0] + PersonName[1]; //which should result in 'firstname lastname'

I get a Access Violation or 'External:SIGSEGV' with dbg.
The person database has the fields id, firstname and lastname and there is a record with the provided person id.
I am in doubt about my use of the lookup method, but I can't find an example of its proper use anywhere, and if I look in the code of the method then my use should be more or less correct.
What am I doing wrong in these lines?

[AlZuur]

Sorry for that. After a good night sleep, it turned out that I had the

Code: [Select]

PersonDbf := TDbf.Create(nil) in the wrong place  . The code in my original post works quite well, thank you.

Regards.