1. An apparatus comprising: a processing platform configured to implement a cluster labeling system for documents comprising unstructured text data from a service events database; the unstructured text data comprising unstructured service request summaries relating to respective service events; wherein the cluster labeling system comprises: a clustering module implementing a topic model generator and being configured to assign each of the documents to one or more of a plurality of clusters based at least in part on one or more topics identified from the unstructured text data using at least one topic model provided by the topic model generator; a visualization module comprising multiple view generators, the multiple view generators being configured to generate respective distinct visualizations of a selected one of the clusters; and a labeling interface permitting user entry of a label for the selected cluster; wherein the multiple view generators comprise at least: a bigram view generator configured to provide a visualization of a plurality of term pairs from the selected cluster; and a summarization view generator configured to provide a visualization of representative term sequences from the selected cluster; wherein the cluster labeling system is further configured to update the service events database to indicate a user-entered label for the selected cluster; and wherein the processing platform comprises one or more processing devices each comprising a processor coupled to a memory.