11. An apparatus, comprising: one or more processors; memory; and a program module, wherein the program module is stored in the memory and, during operation of the apparatus, is executed by the one or more processors to translate a first query into an edge query, the program module including: instructions for receiving the first query, wherein the first query is associated with a first type of database; instructions for translating the first query into the edge query, wherein: the edge query is associated with a graph database storing a graph; and the graph comprises nodes, edges between the nodes, and predicates to represent data with index-free adjacency; instructions for executing the edge query against the graph database, wherein the edge query identifies an edge associated with a predicate that specifies one or more of the nodes of the graph; and instructions for receiving a result in response to the edge query.
11. An apparatus, comprising: one or more processors; memory; and a program module, wherein the program module is stored in the memory and, during operation of the apparatus, is executed by the one or more processors to translate a first query into an edge query, the program module including: instructions for receiving the first query, wherein the first query is associated with a first type of database; instructions for translating the first query into the edge query, wherein: the edge query is associated with a graph database storing a graph; and the graph comprises nodes, edges between the nodes, and predicates to represent data with index-free adjacency; instructions for executing the edge query against the graph database, wherein the edge query identifies an edge associated with a predicate that specifies one or more of the nodes of the graph; and instructions for receiving a result in response to the edge query. 16. The apparatus of claim 11 , wherein the program module further includes instructions for: defining a compound relationship in the graph using the primitives; and generating a compound key to identify the compound relationship.