SECRET DECISION TREE LEARNING APPARATUS, SECRET DECISION TREE LEARNING SYSTEM, SECRET DECISION TREE LEARNING METHOD, AND PROGRAM

1 . A secret decision tree learning device for learning a decision tree by secret calculation, comprising:

a memory; and

a processor configured to execute;

inputting a data set composed of a plurality of records including one or more attribute values of explanatory variables and attribute values of objective variables; and

learning the decision tree by collectively dividing the data set at all nodes included in a hierarchical level, for each of a plurality of hierarchical levels of the decision tree.

2 . The secret decision tree learning device according to claim 1 , wherein the processor collectively divides the data set into smaller groups at all the nodes included in the hierarchical level by using the data set divided into one or more groups in a preceding hierarchical level and a group information vector representing groups to which the records included in the data set belongs, for each of the plurality of hierarchical levels of the decision tree.

3 . The secret decision tree learning device according to claim 2 , wherein the data set is configured to have records belonging to a same group arranged consecutively, and

wherein the group information vector is a vector in which an element corresponding to a last record among the records belonging to the same group among the records configuring the data set is set to 1, and an element other than the element corresponding to the last record is set to 0.

4 . The secret decision tree learning device according to claim 2 , wherein the hierarchical level is defined as i (where i=1, . . . , h), and

wherein the processor calculates a parameter [p i ] representing a division condition at each node included in an hierarchical level i by using a data set [T i ] divided into one or more groups in the preceding hierarchical level and a group information vector [g i ] representing the one or more groups to which records included in the data set [T i ] belong,

classifies the records included in the data set [T i ] into nodes of a hierarchical level i+1 by using the data set [T i ] and the parameter [p i ], and

repeats, for each of the hierarchical levels i, calculation of the data set [T i+1 ] and the group information [g i+1 ] by using the data set [T i ], the parameter [p i ], a result of the classification, and information indicating nodes into which the records included in the data set [T i ] are classified.

5 . A secret decision tree learning system for learning a decision tree by secret calculation, comprising:

a computer including a memory and a processor configured to execute;

inputting a data set composed of a plurality of records including one or more attribute values of explanatory variables and attribute values of objective variables; and

learning the decision tree by collectively dividing the data set at all nodes included in a hierarchical level, for each of a plurality of hierarchical levels of the decision tree.

6 . A secret decision tree learning method for learning a decision tree by secret calculation, executed by a computer including a memory and a processor, the secret decision tree learning method comprising:

inputting a data set composed of a plurality of records including one or more attribute values of explanatory variables and attribute values of objective variables; and

learning the decision tree by collectively dividing the data set at all nodes included in a hierarchical level, for each of a plurality of hierarchical levels of the decision tree.

7 . A non-transitory computer-readable recording medium having computer-readable instructions stored thereon, which when executed, cause a computer to function as the secret decision tree learning device according to claim 1 .