Create a connection between two container?

I got 2 data source container..

How could a create a connection between two containers. I mean if one container is updated, the other will be updated automatically and vise versa.

For example, one container has a string, the other container has two strings(string1 and string2) as two properties.

Then I write string = string1 + string2. I want two containers to be connected.

How could I do it?