There is a data type, that we may call "hierarchical log data", which arises across a wide range of societal networks. It consists of event records in a complex structured activity by an agent. Examples: a commuter makes trips, and for each trip there are tap-in and tap-out events recorded; a user sends requests to a web service, and this triggers a cascade of internal requests in a data center each of which is logged; a person engages in a sequence of purchases in order to complete a project and the credit card purchases are all logged.

Hierarchical log data is central to the understanding of societal networks. Yet it has received very little attention, neither in the database community, nor in data science, nor machine learning. I will describe the challenges, share a dataset, and suggest and some ways forward.

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