The current interfaces to access terms (`LabelsProvider`, `DescriptionsProvider` and `AliasesProvider`) all state in their contract: "It is not guaranteed that this method returns the original object." This is a problem because with that sentence we cannot rely on the fact that changes made to the `TermList` returned by the method are visible to the provider.
We have three options so solve this issue:
* We can either create a second list of interfaces called `LabelsHolder`, `DescriptionsHolder` and `AliasesHolder`. This is how we solved the issue for `Fingerprint` and `StatementList`. The disadvantages are that we get the overhead of three additional types and that we have to call the setter everytime we want to change someting. Code will always be like `$var = $obj->getFoo(); $var->setBar( 'baz' ); $obj->setFoo( $var );`.
* Another option is to change the contract of the interfaces so that they always return a reference to the original object in the provider. We can then be sure that all changes are visible to the provider. However, there is no option to replace the entire object in case we want to clear the list (for example).
* Third option would be to merge all the "provider" and "holder" interfaces. We than don't have the choice to provide immutable providers but we don't have the overhead of three (+two) additional interfaces.
It would be great to get some opinions on this question so that we can make a decision on the architecture of our data model.