A method and system for managing access to data. A plurality of data items is stored across a plurality of partitions according to a graph-based data model. The data model associates each data item with an identifier of a source entity pertaining to the data item, an identifier of a destination entity pertaining to the data item, and an identifier of a type of directed relationship pertaining to the data item from the source entity to the destination entity. When a lookup request is received identifying a source entity and a type of directed relationship from the source entity, a particular partition is identified based on the source entity identifier. A response to the lookup request is then returned that includes data item(s) from the identified partition that are associated in the partition with both the identified source entity identifier and the identified directed relationship type.