Compound (grouped) attributes

[stemkovs]

In some use cases "matching" data is spread between several attributes.
For example, let's look at a use case with 3 indexes: people and cars
people index contains person_name, DOB, and address fields
cars index contains person_name, DOB, and car's license_plate fields
We would like to be able to find all people living at a particular address and all cars connected to these people. At the first glance, two resolvers should suffice:

1. address
2. person_name + DOB
   The first resolver will give us all people living at a particular address and the second resolver will pull out license plates for cars connected to these people.

The problem appears when a person (person-A) who lives at address-A, shares the same name with another person (person-B1) and shares the same DOB with yet another person (person-B2), where person-B1 and person-B2 happen to live at the same address-B. If we search for data starting from address-B, we are going to find person-B1 and person-B2 (correctly), but then by combining name of person-B1 and DOB or person-B2 we'll find person-A (incorrectly).

To avoid this issue there need to be a way for marking person_name and DOB attributes as "compound" or "grouped", so name and DOB of a person to look for would always come from the same record.