Thanks Nya, however it was not this I was looking for. I am very well aware of Duplicate Detection rules.
My requirement is more or less what Bipin is coming up with.
1) Let's say - I've X Entity with two lookups to Contact entity.
2) I've connection already present on those contacts lookup value selected.
3) Requirement is from X Entity if I go and select again those two contacts from lookups then find out if connection exists and if 'Yes' - hide field of 'create connection' flag or else Show the flag field.
Thanks all but waiting...
Nikhil