Usage of implementsInterface element on entities in guidewire

I would like to know why do we use implementsInterface element in entities. I know one example where they use it to make it as assignable entity. But I could not understand what other purpose and how/why it is being used in entities.

Example: Injuryincident entity has claimantsupplier and coveragesupplier interface

I like to see it from this prespective, simplified and assuming that you have some java background:

As you probably already know it, having an entity means in the end of the day, having a Java class... Well, by using the implementsInterface element in your entity, is similar to implement an interface in you java class.

Here you have a quick example...

Consider the following:

MyEntiti.eti

<?xml version="1.0"?>
<entity
  xmlns="http://guidewire.com/datamodel"
  entity="MyEntity"
  table="myentity"
  type="retireable"/>

AnInterface.gs

package mypkg
interface AnInterface {
  function doSomething()
}

AnInterfaceImpl.gs

package mypkg

class AnInterfaceImpl implements AnInterface {
  override function doSomething() {
    print("Hello!")
  }
}

Image that you need MyEntity to have the ability of "doSomething", you just need to add the implementsInterface:

<?xml version="1.0"?>
<entity
  xmlns="http://guidewire.com/datamodel"
  entity="MyEntity"
  table="myentity"
  type="retireable">
  <implementsInterface
    iface="mypkg.AnInterface"
    impl="mypkg.AnInterfaceImpl"/>
</entity>

By doing that, the following code must work:

var myEntity = new MyEntity()
myEntity.doSomething() //this will call the  method defined in the interface-implementation

And even better, you migth let you implementation to recognize the related object of MyEntity and use it as per your needs:

package mypkg

class AnInterfaceImpl implements AnInterface {
  
  private final var  _relatedEntity : MyEntity

  construct(relatedTo : MyEntity) {
    _relatedEntity = relatedTo 
  }

  override function doSomething() {
    var createUser = _relatedEntity.CreateUser // you can accees to whatever you need
    print("Hello!, this is the related instace of MyEntity: ${_relatedEntity}")
  }
}

Hope it helps, regards!