Query Engines are algorithms for responding to questions with the answers the asker wants, rather than the answers they asked for.
In domains with large, dense, complex data sets, having an algorithm "on the ground" that understands the data is absolutely critical for getting a reasonable response.
An easy example might be "where should I go for lunch?"
The responses need to be adjusted by many factors. Distance, food type, whether it's open, whether it's too crowded or expensive. These factors are deeply entangled with the state of the person asking the question as well as the state of the data used to respond meaningfully.
That's the role of a query engine.
Query engines are used everywhere. For example, every infomorph integrates several.
Relation to Studies in the Bottlenose Nebula
Query engines are used by every scientist in the region. Questions are asked of the Hypernet, and data is submitted following Universal Scientific Communication Standards to allow easy integration with commonly used query engines other scientists will use to ask questions of the hypernet.
Query engines are frequently developed by subluminal civilizations, typically as they begin to develop computers and worldwide networks. Poor query engine policy can lead to issues such as the Isolation Initiatives, Bandu Regressions, or catastrophes such as The Great Teacher.
But species can benefit greatly from unusually capable query engines, as well. There is no better example of that than the Utilitons.