According to server architecture, plugins can be of the following types:
Collectors are designed to collect information; analyzers – to analyze it and form some other data on its basis; persistors – to save information from the common dictionary into files, databases, etc.; notifiers - to notify system users about any events.
This division is rather arbitrary. There is an opportunity to execute all the actions on collection, analysis and saving the information in one and only plugin. But at the same time the division into functionally independent parts allows to build flexible and easily configurable system for collecting and processing the data.
Also it is possible to implement the systems of lazy-write, planning of collecting/processing tasks and notifying users about different events.