ServiceNow Discovery can be extended in three main ways: Classifiers, Probes & Sensors, and Discovery Patterns. Classifiers are used to identify the type of device or application that is being discovered, based on the information returned by a probe. Probes are commands or scripts that are executed on the target device or application to collect data. Sensors are scripts that process the data collected by probes and create or update configuration items (CIs) in the CMDB. Discovery Patterns are graphical representations of the discovery process that can be customized or created to discover specific types of devices or applications, using classifiers, probes, and sensors as building blocks.