Aspects of the present disclosure provide techniques for executing requests in an object schema-based application programming interface (API) based on union relationships between data objects. Embodiments include receiving an API query from a client application. The API query identifies a navigable path through a graph projection of the API and includes a plurality of nodes in the graph. One or more data objects to resolve in order to satisfy the API query are identified based on an object schema associated with each node in the query. For each respective data object of the one or more data objects, one or more services associated with properties of the respective data object are identified, and one or more subqueries are generated to the services to satisfy the properties of the respective data object. The subqueries are transmitted to the identified services for execution, and a result of the API query is returned.