1. A computer-implemented system comprising: a graph mapper configured to store data representing a graph into a first table in a relational database, each node in the graph having a single-valued property and a multi-valued property, the multi-valued property being a non-local property and containing a reference to at least one adjacent node, the mapper configured to store each node in a corresponding record in the first table by: storing the single-valued property in a single-valued field, and storing the multi-valued property in a multi-valued field; and a query translator configured to: receive a graph query on the graph, the query including a traversal from a first node to a second node that is adjacent to the first node, and convert the graph query into a structured query language (SQL) query over the first table and a second table, the SQL query retrieving the multi-valued property of the first node from the first table and obtaining data of the second node from the second table.