An enumeration plan generation unit 81 generates a set of logical formula structures each representing a way of combining logical formula expressions each representing a combination of features by use of the features of learning data items and the maximum number of features to be combined, and generates partial logical formula structures by dividing a logical formula expression included in each of the generated logical formula structures into two, and generates an enumeration plan in which the partial logical formula structures are linked to the logical formula structure from which the partial logical formula structures are divided. The feature generation unit 82 generates a new feature that is a combination of the features corresponding to the generated partial logical formula structures. Furthermore, the enumeration plan generation unit 81 divides the logical formula structure into two such that the numbers of the features included in the two partial logical formula structures generated from each of the logical formula structures are substantially equal.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. A feature enumeration system comprising: hardware including a processor; an enumeration plan generation unit implemented at least by the hardware and that generates a set of logical formula structures each representing a way of combining logical formula expressions each representing a combination of features by use of features of learning data items and a maximum number of features to be combined, generates partial logical formula structures by dividing a logical formula expression included in each of the generated logical formula structures into two, and generates an enumeration plan in which the partial logical formula structures are linked to the logical formula structure from which the partial logical formula structures are divided; and a feature generation unit implemented at least by the hardware and that generates a new feature that is a combination of the features corresponding the generated partial logical formula structure, wherein the enumeration plan generation unit divides the logical formula structure into two such that numbers of the features included in the two partial logical formula structures generated from each of the logical formula structures are substantially equal. 2. The feature enumeration system according to claim 1, wherein the enumeration plan generation unit generates an enumeration plan in which a relationship between the logical formula structure and the generated partial logical formula structures each representing a part of the logical formula structure is represented as a graph structure, and selects the partial logical formula structures from the enumeration plan such that a size of a space necessary to store the new feature generated by the feature generation unit is able to be reduced and more parts of the logical formula structure are able to be represented. 3. The feature enumeration system according to claim 2, wherein the feature generation unit stores a new feature generated in accordance with the partial logical formula structures selected by the enumeration plan generation unit in a storage device, and generates a new feature corresponding to other logical formula structures based on the features stored in the storage device. 4. The feature enumeration system according to claim 1, further comprising: a feature assessment unit implemented at least by the hardware and that assesses the feature generated by the feature generation unit, wherein, every time the feature generation unit generates a new feature corresponding to each of the partial logical formula structures, the feature generation unit transmits the generated new feature to the feature assessment unit. 5. The feature enumeration system according to claim 1, wherein the enumeration plan generation unit uses a Disjunctive normal form or a Conjunctive normal form as the logical formula expression representing a combination of the features. 6. A feature enumeration system comprising: hardware including a processor; an enumeration plan generation unit implemented at least by the hardware and that generates a set of logical formula structures each representing a way of combining logical formula expressions each representing a combination of features by use of features of learning data items and a maximum number of features to be combined, and generates an enumeration plan in which a relationship between the logical formula structure and the generated partial logical formula structures each representing a part of the logical formula structure is represented as a graph structure; and a feature generation unit implemented at least by the hardware and that generates a new feature that is a combination of the features corresponding to the partial logical formula structures, wherein the enumeration plan generation unit selects the partial logical formula structures from the enumeration plan such that a size of a space necessary to store the new feature generated by the feature generation unit is able to be reduced and more parts of the logical formula structure are able to be represented. 7. The feature enumeration system according to claim 6, wherein the feature generation unit stores a new feature generated in accordance with the partial logical formula structures selected by the enumeration plan generation unit in a storage device, and generates a new feature corresponding to other logical formula structures based on the features stored in the storage device. 8. A feature enumeration method comprising: generating a set of logical formula structures each representing a way of combining logical formula expressions each representing a combination of features by use of features of learning data items and a maximum number of features to be combined; generating partial logical formula structures by dividing a logical formula expression included in each of the generated logical formula structures into two, and generating an enumeration plan in which the partial logical formula structures are linked to the logical formula structure from which the partial logical formula structures are divided; and generating a new feature that is a combination of the features corresponding to the generated partial logical formula structures, wherein, when the enumeration plan is generated, the logical formula structure is divided into two such that numbers of the features included in the two partial logical formula structures generated from each of the logical formula structures are substantially equal. 9. The feature enumeration method according to claim 8, further comprising: generating an enumeration plan in which a relationship between the logical formula structure and the generated partial logical formula structures each representing a part of the logical formula structure is represented as a graph structure; and selecting the partial logical formula structures from the enumeration plan such that a size of a space necessary to store the generated new feature is able to be reduced and more parts of the logical formula structure are able to be represented. 10. A feature enumeration method comprising: generating a set of logical formula structures each representing a way of combining logical formula expressions each representing a combination of features by use of features of learning data items and a maximum number of features to be combined; generating an enumeration plan in which a relationship between the logical formula structure and the generated partial logical formula structures each representing a part of the logical formula structure is represented as a graph structure; selecting the partial logical formula structures from the enumeration plan such that a size of a space necessary to store the new feature generated in accordance with the partial logical formula structures is able to be reduced and more parts of the logical formula structure are able to be represented; and generating a new feature that is a combination of the features corresponding to the partial logical formula structures. 11. The feature enumeration method according to claim 10, further comprising: storing a new feature generated in accordance with the selected partial logical formula structures in a storage device and generating a new feature corresponding to other logical formula structures based on the features stored in the storage device. 12. A non-transitory computer readable information recording medium storing a feature enumeration program, when executed by a processor, that performs a method for: generating a set of logical formula structures each representing a way of combining logical formula expressions each representing a combination of features by use of features of learning data items and a maximum number of features to be combined, and generating the partial logical formula structures by dividing a logical formula expression included in each of the generated logical formula structures into two and linking the partial logical formula to the logical formula structure from which the partial logical formula structures are divided, to generate an enumeration plan; and generating a new feature that is a combination of the features corresponding to the generated partial logical formula structures, wherein the logical formula structure is divided into two such that numbers of the features included in the two partial logical formula structures generated from each of the logical formula structures are substantially equal. 13. The non-transitory computer-readable recording medium according to claim 12, generating an enumeration plan in which a relationship between the logical formula structure and the generated partial logical formula structures each representing a part of the logical formula structure is represented as a graph structure, and selecting the partial logical formula structures from the enumeration plan such that a size of a space necessary to store the new generated feature is able to be reduced and more parts of the logical formula structure are able to be represented. 14. A non-transitory computer readable information recording medium storing a feature enumeration program, when executed by a processor, that performs a method for: generating a set of logical formula structures each representing a way of combining logical formula expressions each representing a combination of features by use of features of learning data items and a maximum number of features to be combined, and generating an enumeration plan in which a relationship between the logical formula structure and the generated partial logical formula structures each representing a part of the logical formula structure is represented as a graph structure; and generating a new feature that is a combination of the features corresponding to the partial logical formula structures, wherein the partial logical formula structures are selected from the enumeration plan such that a size of a space necessary to store the new generated feature is able to be reduced and more parts of the logical formula structure are able to be represented. 15. The non-transitory computer-readable recording medium according to claim 14, storing a new feature generated in accordance with the selected partial logical formula structures in a storage device and generating a new feature corresponding to other logical formula structures based on the features stored in the storage device.