Disclosed is a method of accessing a network of relationship instances and data field values of entity instances in a combined entity relationship- and relational-model database management system. The method comprises the steps of receiving a query that natively references relationship types including data fields to be accessed; parsing the query into a parse tree; converting the parse tree to a query graph; optimising the query graph by consolidating equivalent nodes in the query graph; analysing the nodes in the optimised query graph; codifying each node of the optimised query graph into a first table of state transition rules; codifying the data fields to be accessed into a second table of field rules; preparing a query that includes the first and second tables; identifying entity instances to be accessed by the prepared query by iteratively following relationship instances according to the first table; and loading data fields of the identified entity instances according to the second table.