Methods and arrangements involving portable devices, such as smartphones and tablet computers, are disclosed. In a particular embodiment, a system stores information from a sensor sub-system as RDF triples. The sensor sub-system may comprise a physical or logical sensor, such as a camera, a microphone, an accelerometer, a GPS receiver, an image classifier, and a user activity sensor. The triples can be stored in a user's smartphone or other portable device, or in the cloud. The stored data can then be acted on by a processor—again, in the user's smartphone, in another portable device, or in the cloud. A great variety of other features and arrangements are also detailed.