||This paper proposes a sensor database system KRAFT. KRAFT is a database system that supports a variety of sensor data, and provides the following features: (1)freshness for sensor data without losing persistence,
(2)abstract data type for sensor data, and (3)continual monitoring. To provide the feature (1), KRAFT uses remote memory as WAL files instead of local disk. Each log record is sent to a remote log server with TCP concurrently. At recovery, all of the log records at the remote log server are collected and sorted by ascending time order and sent back idempotently to the database server. To provide the feature (2), KRAFT extends relational data model, and permits users to make SENSOR TYPE to retrieve similar sequences with euclid or dynamic time warping metric and to retrieve the last sensor data. To provide the feature (3), KRAFT permits to make MONITOR that periodically executes query inside KRAFT. We applied KRAFT for a humanoid robot called Robovie, and measured the staleness of sensor data. The results of experiments indicated that KRAFT provides good freshness of sensor data and good scalability.