The RDF world has conclusively proven that there is more than "One Graph". (e.g. people try to make "One Graph" and their projects die; try to make as many graphs as there are points of view and the sailing is smooth)
I'll never forgive them for taking a great concept and absolutely beating it to death with intellectual (for lack of a better word) wankery. We could have ubiquitous Datomic style triple stores today if not for the Semantic Web researcher's need to generate pseudo-academic journal articles.
In terms of maintainability, you have to take care that your changes to the underlying business logic don't break assumptions of each schema. And if you want to evolve one schema (eg. say, deprecate a mutation argument, rename a field and deprecate the old naming), you have to ensure that your underlying business logic is backwards compatible for any other schemas (and their clients) relying on it.
It is relatively easy to do this in the RDF world since the graph is composed of individual facts which may or may not be in a particular graph.