An information processing device includes a keyword acquiring unit configured to acquire a plurality of primary keyword and secondary keyword groups; a classifying unit configured to classify each of the plurality of secondary keywords by a plurality of topics; an estimating unit configured to estimate whether or not each primary keyword in the plurality of groups is a related keyword related to any topic having a classified secondary keyword or a mixed keyword unrelated to any of the topics; and an assigning unit configured to preferentially assign a primary keyword estimated to be a related keyword to a topic having a classified secondary keyword in the same group, and assigning a primary keyword estimated to be a mixed keyword to any of all the topics given for classification.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. An information processing device, comprising: a keyword acquiring unit configured to acquire a plurality of primary keyword and secondary keyword groups; a classifying unit configured to classify each of the plurality of secondary keywords by a plurality of topics; an estimating unit configured to estimate whether or not each primary keyword in the plurality of groups is a related keyword related to any topic having a classified secondary keyword or a mixed keyword unrelated to any of the topics; and an assigning unit configured to preferentially assign a primary keyword estimated to be a related keyword to a topic having a classified secondary keyword in the same group, and assigning a primary keyword estimated to be a mixed keyword to any of all the topics given for classification. 2. The information processing device of claim 1, wherein: the assigning unit determines a topic to assign a primary keyword estimated to be a related keyword on the basis of the proportion of secondary keywords classified by each topic in the same group; and determines a topic to assign a primary keyword estimated to be a mixed keyword irrespective of the proportions. 3. The information processing device of claim 1, wherein the keyword acquiring unit acquires primary document information including more than one primary keyword, and secondary document information including more than one secondary keyword created by a user. 4. The information processing device of claim 3, wherein the estimating unit estimates whether or not a primary keyword is a related keyword or a mixed keyword on the basis of primary topics having assigned primary keywords and secondary topics having assigned secondary keywords. 5. The information processing device of claim 4, wherein the estimating unit comprises: a topic acquiring unit configured to acquire a primary topic of the primary keyword; a match calculating unit configured to calculate the extent of the topic match being the proportion of secondary topics assigned to one or more secondary keywords that are the same as the primary topic; a mixed keyword ratio acquiring unit configured to acquire the mixed keyword ratio or the ratio of primary keywords estimated to be mixed keywords among primary keywords included in primary document information from all users; and a mixed keyword probability calculating unit configured to calculate the mixed keyword probability of the primary keyword being a mixed keyword on the basis of the extent of the topic match and the mixed keyword ratio. 6. The information processing device of claim 5, wherein the estimating unit further comprises a mixed keyword determining unit configured to determine whether a primary keyword is a related keyword or a mixed keyword on the basis of the mixed keyword probability. 7. The information processing device of 4, further comprising a primary keyword appearance calculating unit configured to calculate the likelihood Ψkt of the tth primary keyword t, wherein t is an integer>1, appearing in the kth topic, wherein k is a predetermined integer>1, in all sets of primary document information from a user. 8. The information processing device of claim 7, further comprising a topic probability generating unit configured to generate the probability θdk of the kth topic k in each set of secondary document information d, wherein d>1 but less than the total number of sets of secondary document information being generated. 9. The information processing device of claim 8, further comprising a primary keyword generation probability calculating unit configured to calculate a primary keyword generation probability P(t|d, D) of a primary keyword t being assigned to a single set of secondary document information d by totaling the θdkΨkt of each topic k in the set of secondary document data d. 10.-18. (canceled) 19. A non-transitory, computer readable storage medium having instructions stored thereon that when executed by a computer, implement an information processing method, the method comprising: acquiring a plurality of primary keyword and secondary keyword groups; classifying each of the plurality of secondary keywords by a plurality of topics; estimating whether or not each primary keyword in the plurality of groups is a related keyword related to any topic having a classified secondary keyword or a mixed keyword unrelated to any of the topics; and assigning a primary keyword estimated to be a related keyword to a topic having a classified secondary keyword in the same group, and assigning a primary keyword estimated to be a mixed keyword to any of the topics for classification. 20. The storage medium of claim 10, wherein the method further comprises: determining a topic to assign a primary keyword estimated to be a related keyword on the basis of the proportion of secondary keywords classified by each topic in the same group; and determining a topic to assign a primary keyword estimated to be a mixed keyword irrespective of the proportions.