1. An information presenting device for presenting a relationship between pluralities of data pieces, each plurality of data pieces of the pluralities of data pieces being held by a respective one of a plurality of users, the information presenting device comprising: an acquiring unit operable to acquire at least (i) a first information group including a first plurality of data pieces, each data piece of the first plurality of data pieces being held by a first user and having a first attribute and a second attribute attached thereto, and (ii) a second information group including a second plurality of data pieces, each data piece of the second plurality of data pieces being held by a second user and having the first attribute and the second attribute attached thereto; a generating unit operable to, (i) with respect to each different attribute value of a plurality of different attribute values of the first attribute, extract data pieces, of the first plurality of data pieces, having a same attribute value of the first attribute from the first information group so as to generate respective first subgroups each consisting of the data pieces having the same attribute value of the first attribute extracted from the first information group and (ii), with respect to each different attribute value of a plurality of different attribute values of the first attribute, extract data pieces, of the second plurality of data pieces, having a same attribute value of the first attribute from the second information group so as to generate respective second subgroups each consisting of the data pieces having the same attribute value of the first attribute extracted from the second information group; a calculating unit operable to, with respect to each of one or more pairs of the generated first and second subgroups pertaining to a same attribute value of the first attribute from among all of the first and second subgroups generated by the generating unit, calculate a commonality between attribute values of the second attribute attached to the data pieces of the first subgroup and attribute values of the second attribute attached to the data pieces of the second subgroup, for each of different attribute values of the second attribute; a determining unit operable to determine a presentation order in which to present all of the commonalities calculated by the calculating unit, the presentation order being determined based on how many data pieces are contained in each of the one or more pairs of the generated first and second subgroups; and a presenting unit operable to present the commonalities calculated by the calculating unit arranged in the presentation order determined by the determining unit.