Introduction: The discovered frequent graph patterns and/or their variants can be used as features for graph classification. First, we mine frequent graph patterns in the training set. The features that are frequent in one class but rather infrequent in the other class (es) should be considered as highly discriminative features. Such features will then be used for model construction.
To achieve high-quality classification, we can adjust the thresholds on frequency, discriminativeness, and graph connectivity based on the data, the number and quality of the features generated, and the classification accuracy.
Various classification approaches, including support vector machines, naïve Bayesian, and associative classification, can be used in such graph-based classification.
Similarly, cluster analysis can be explored with mined graph patterns. The set of graphs that share a large set of similar graph patterns should be considered as highly similar and should be grouped into similar clusters. Notice that the concept of graph connectivity (or minimal cuts) introduced in the section for mining frequent dense graphs can be used as an important measure to group similar graphs into clusters. In addition, the minimal support threshold can be used as a way to adjust the number of frequent clusters or generate hierarchical clusters. The graphs that do not belong to any cluster or that are far away from the derived clusters can be considered as outliers. Thus outliers can be considered as a by-product of cluster analysis.
Many different kinds of graphs can be discovered in graph pattern mining, especially when we consider the possibilities of setting different kinds of thresholds. Different graph patterns may likely lead to different classification and clustering results, thus it is important to consider mining graph patterns and graph classification/clustering as an intertwined process rather than a two-step process. That is, the qualities of graph classification and clustering can be improved by exploring alternative methods and thresholds when mining graph patterns.
