UCS2007 -- RFID Privacy Using Spatially Distributed Shared Secrets -- Context Adapted Certificate Using Morph Template Signature for Pervasive Environments -- Handling Spatio-temporal Sensor Data in Global Geographical Context with SENSORD -- Context Awareness by Case-Based Reasoning in a Music Recommendation System -- Developing Intelligent Smart Home by Utilizing Community Computing -- Instant Learning Sound Sensor: Flexible Real-World Event Recognition System for Ubiquitous Computing -- D-FLER - A Distributed Fuzzy Logic Engine for Rule-Based Wireless Sensor Networks -- Secure and Reliable Data Aggregation for Wireless Sensor Networks -- The iNAV Indoor Navigation System -- C-ANIS - A Contextual, Automatic and Dynamic Service-Oriented Integration Framework -- Using Auction Based Group Formation for Collaborative Networking in Ubicomp -- A Software Architecture for Virtual Device Composition and Its Applications -- Ubiquitous Communication Services Based on Effective Knowledge Deployment -- Detection of User Mode Shift in Home -- Discriminative Temporal Smoothing for Activity Recognition from Wearable Sensors -- Activity Recognition Based on Intra and Extra Manipulation of Everyday Objects -- Towards an Activity-Aware Wearable Computing Platform Based on an Egocentric Interaction Model -- mCube - Towards a Versatile Gesture Input Device for Ubiquitous Computing Environments -- uPackage - A Package to Enable Do-It-Yourself Style Ubiquitous Services with Daily Objects -- DroPicks - A Tool for Collaborative Content Sharing Exploiting Everyday Artefacts -- Place Recognition Using Multiple Wearable Cameras -- Compact Data Format for Advertising and Discovery in Ubiquitous Networks -- A Media Access Protocol for Proactive Discovery in Ubiquitous Wireless Networks -- Mobility Helps DataDelivery in Disruption Tolerant Networks.

We cordially welcome you to the proceedings of the 2007 International S- posium on Ubiquitous Computing Systems (UCS) held at Akihabara, Tokyo, Japan. UCS has become a symposium for the dissemination of state-of-the-art research and engineering practices in ubiquitous computing with particular - phasis on systems and software. UCS 2007 was the fourth of this series of int- nationalsymposia.ThiswastheyearfortheNextGenerationNetwork(NGN)to be commercially launched so that the Internet could become the infrastructure forcommunicationsandcomputingsubstitutingtheNGNintelephonenetworks. The maturity of the Internet encourages the research and development of the nextcomputing systems,where ubiquitous computing is recognizedasone ofthe most promising computing paradigms. This symposium was organized by IPSJ SIGUBI, IEICE USN and UCN, Korea, in cooperation with the IEEE Tokyo Section, IPSJ SIGEMB, IEICE Smart Info-media Systems Technical Group, and Human Interface Society. It was also sponsored by Ubiquitous Networking Forum, Nokia, NTT, SCAT, IISF and TAF. Thisyear,wehad96submissionsfrom18countries.TheProgramCommittee reviewed all the papers carefully and then selected 16 full papers and 8 short papers. The very low acceptance rate of about 22.6% clearly demonstrates the high quality of the conference, and this tradition will continue in the upcoming conferences. Two distinguished speakers were also invited for keynote speeches, who enlightened the audience on ubiquitous computing and applications. The high-quality technical program of UCS 2007 depends very much on the precise and stringent review process. The Technical Program Committee c- sistedof62excellentmembers.Mostreviewswarealmostofjournalpaperreview quality, and the paper selection was very serious and strict. Along with the symposium, we also o?ered a workshop and a poster session.