How is a user session defined in OneSearch? I have been using Primo Analytics for total searches in OneSearch and these search numbers are very different from the user sessions.
OneSearch/Primo Analytics Searches are indeed quite different from Google Analytics Sessions.
A session can be understood as a site "visit." In general terms, a session is a group of interactions that take place on the website within a given time frame. Whatever the user does on the site during this period is considered part of a single session. A single session can contain multiple screen or page views. It can involve multiple searches and/or going to a user’s account to look at what books are due.
A search, in Primo terms, is an individual search. However, it is also almost any activity in Primo that results in updating search results. For example, clicking on "next page" or "previous page" is also counted as a search. One could call these individual search events.
Another way to approach this question is to ask, what is a search in human terms? One could argue that a session is a better representation of how people use the system. If the goal of a OneSearch visit is to research a topic, then it is reasonable, in human terms, to consider a single session as a realistic representative of a single “search” of this type -- even if the site visit involved 10 "Primo" search events.
Some casual comparisons indicate that a OneSearch session tends to represent, on average, about 3 searches in Primo Analytics.
Whichever number is used to measure traffic, the important point is to use 1 measure consistently.