Relate two fields on a Table

Hello Guys,

This is Rakesh, am a trainee consultant Axapta 2009. I have gone through tables MarkupTrans and MarkupTable.

In the Markuptrans Table whenever we change the "Markupcode" field on the field, there is change in corresponding  "Txt" field.

Can anyone help me in understanding the concept?

Thanks & Regards,

Rakesh