Hi , i have three CDT'S namely 1 , 2 and 3 . I want to define them in a way

Have a look at the recent Tips & Tricks Webinar. I think that should help you.

What is the issue you're having here? If you look at Appian documentation on defining relationship, it talks about configuring one to many relationship. Its simply a matter of creating the complex time and defining it as maxOccurs-"unbounded" minOccurs="0" (if its optional).

@sathya: I am facing an issue while writing to one of my data store , and i am not able to find a concrete solution to it . Can you help me with it?

What's your issue? Can you share your XSD definition as well?

yes my issue is i have five cdt's : A,B,C,D,E ; the relationships between them are 'A' has one to many relationship with 'B' , 'B' has one to many relationship with 'C' ,'C' has one to one relationship with 'D' , 'E' has one to many relationship with 'C' .
And i have a data store having entity of each A, B ,C ,D,E.
Now when i am populating my tables , I used the CDT of type 'A' and data store entity of 'A' and was successfully able to populate both A and B tables. (as A has one to many relation with B )
Now when i tried to populate my table C , i tried to follow the same thing , use the CDT of type B and data store of type B ,but it was giving me an error . Then i used CDT of type B and data store entity of C and still it gave me an error.Then i used CDT of type C and data store entity of C ,the table C was populated but its reference of B was still empty so i had to use a query service to update that column separately .Now my question is can i not populate the C in one go as i was able to populate B with its reference .
I hope i am able to explain my query

I think I understand your explanation. Firstly, maintaining such a relationship is a not a good design practice. The design will pull large amount of data from the database and same while persisting it. I would recommend no more than 1 level of nesting. What you can do is to create an ID column in your model that points to its child such that the entity gives you a bunch of child id's and from that, you can use a query rule to pull the child and so on.