The task of a type resolver is to resolve an input type, which is delivered by the invocation chain, into a known GraphQL type defined in the schema, for example, resolve a Content object of the content type CMArticle into the string CMArticleImpl, which is pointing to the implementing GraphQL type in the schema. Now, that the GraphQL runtime "knows" how to use the content object by knowing the implementing type and its properties, the properties can be resolved, using the above described invocation chain.