how to get a values from a sub interface

Hi there,

The code you have written works both ways. 
If you change the value of RI 'a' in 'rule' interface, then that will be reflected in the parent's local!a variable. And vice versa. 

i mean i write in the parent interface only, it can extract child local!value. Is this mean i do not have to change any thing?

You cannot extract the local variables of a child interface. To do so, you need to save them in the rule inputs. 

i mean how to extract a child interface rule input value?

Create a rule input in the child interface and while calling the child from the parent map the variable from the parent. 

Let's get a key concept clear (this may help you conceptual model you use going forwards):

• rule inputs - whether used in User Interfaces or Expression Rules - are references or pointers (in Java terms) to a location where a value is actually stored. That is: a rule input has no actual value of its own

This means that if you want to "fetch" a value form a child component back into the parent component then that value has to exist either as a local! variable in the parent component OR it has to be a rule input to the parent component. Bear in mind that the latter is still a pointer and has to reference a variable somewhere. If your User Interface is the very top level and is being called from a process model then the actual variable is the "Activity Class" variable which is in effect private to the the User Input Task node. You can copy values from process variables to activity class variables and back again using the mapping in the User Input Task.