Thank you for all the replies. As usual there are many ways in PERL to deal with this immediate problem. However, I think my question has now changed to what is the best way to index data.

In my data model I have a Sample that has multiple Tests. When I am working with a Sample object I want to be able to link my Test objects to it in such a way that I can:-
• ask the Sample object to pass over a Test object using a test id e.g. $sample->get_test("a1b2c3").
• return an array of Test objects in order of a value (such as date) which is an attribute of Test.

So I guess my data is structured just like a normalised database and I am looking for the mechanism (not the key) for joining the objects together.

Sorry if I am not making much sense, but thanks for your help.