My current project is a small weather station with distributed sensors. The setup is shown in the block diagram below.
The general idea is quite simple. The Arduino takes measurements roughly every 30 seconds and transmits them to the RaspPi. There, the raw measurements together with the ID of the Arduino (there may be more than one sensor) are collected in a raw data table inside a SQL database. The measurements from the raw data table are read by a CRON job every five minutes to generate average values (5min, 1h and 24h) for each sensor. The results are again stored in different tables. These tables are used by the web pages to show the course of the weather over the last few days. I plan to write a short post on each part of the chain during the next weeks.