1. An information processing device comprising: a hardware processor; and an attribute value estimating unit, implemented on the hardware processor, for estimating an attribute value associated with an estimation target object, based on an attribute value associated with a connection object; wherein the attribute value is a value representing possession or absence of an attribute, the estimation target object is one object in a universal set including a plurality of objects each associated with an attribute value, and the connection object is an object connected with the estimation target object among the objects in the universal set, the information processing device further comprising the attribute value estimating unit for: estimating an attribute value representing the possession of the attribute as the attribute value associated with the estimation target object, in a case that objects associated with the attribute value representing the possession of the attribute are concentratedly located in a connection set composed of the connection objects in the universal set; and determining whether the objects associated with the attribute value representing the possession of the attribute are concentratedly located in the connection set in the universal set, based on an internal density of the universal set and an internal density of the connection set, wherein the internal density of the universal set has a value that becomes larger as a ratio of a number of objects associated with the attribute value representing the possession of the attribute among the objects in the universal set, to a number of the objects in the universal set, becomes larger, and the internal density of the connection set has a value that becomes larger as a ratio of a number of the objects associated with the attribute value representing the possession of the attribute among the objects in the connection set, to a number of the objects in the connection set, becomes larger.