1. A computer-implemented method comprising: obtaining data representing a directed graph, wherein one or more nodes of the graph are associated with a respective set of one or more metric instances, wherein each respective set of metric instances for each node in the graph identifies all metric instances associated with the node and all metric instances associated with any node descendant from the node in the graph, wherein each metric instance identifies a location in a source code base, and wherein each metric instance has a respective metric value, and wherein at least one metric instance is associated with multiple locations in the code base, the multiple locations being represented by multiple nodes in the graph; and computing an aggregated attribute value for a first node in the graph, including aggregating respective metric values of each metric instance in a first set of metric instances associated with the first node, wherein the first set of metric instances identifies all metric instances associated with the first node and all metric instances associated with any node descendant from the first node including the metric instance associated with multiple locations in the code base.