1. A method, comprising: obtaining a collection of clusters of immutable observations about entities, at least a plurality of the clusters each: corresponding to a respective entity, identifying immutable observations determined to describe the respective entity, and having summary attribute-value pairs that summarize the identified observations and collectively describe an inferred current state of the respective entity; receiving a new observation about a given entity; selecting, with one or more processors, a cluster among the collection of clusters based on correspondence of the selected cluster to the given entity; summarizing, with one or more processors, the selected cluster by updating at least some of the summary attribute-value pairs of the selected cluster based on both the new observation and the observations identified by the selected cluster; storing the updated attribute-value pairs in memory in association with the selected cluster; and updating a user interface at a user device using the new observation.