31. The computing system of claim 30 , wherein a first collection of nodes associated with the first mapping rule includes: a first node representing a first relational expression including a relational algebra operation that references the first source entity and the second source entity, a second node linked to the first node representing a relational expression including the first source entity, and a third node linked to the first node representing a relational expression including the second source entity.
32. The computing system of claim 31 , wherein the mapping information includes a second mapping rule that defines a value of an attribute of a destination entity in terms of a value of an attribute of the first source entity.