1. A computer-implemented method of representing a decision tree model in relational form comprising: logically providing a directed acyclic graph comprising a plurality of nodes and a plurality of links, each link connecting a plurality of nodes; encoding a tree structure by including in each node a parent-child relationship of the node with other nodes; encoding in each node information relating to a split represented by the node, the split information including a splitting predictor and a split value or values; and encoding in each node a target histogram.