Need advise for database structure for non linear data.

Hi,

I need advise about a database structure. I need to capture data from the
web about one specific subject on few specific websites and insert that data
to a database. I have done this question here before, but I think I have not
explained very well.

The problem with this task is that the information is not linear, if I try
to design tables with fields for all possible data I will end up with many
row fields with NULL values. There are any problem with this(end up with
many row fields with NULL values)? Or should I user other kind of structure?
For example store the data in one field and that field containing an
associative array with data.

What I mean with non linear data is the following:

array(
'name' => 'Don',
'age' => '31'
);

array(
'name' => 'Peter',
'age' => '28',
'car' => 'ford',
'km' => '2000'
);

In a specific website search I will store only "name" and "age", and in
other website I will store "name", "age", "car" and "km".

I don't know If I explain weel my problem. My english is not very good.

Best Regards.