We can envision that future sensor networks (WSNs) are ubiquitous, large-scale, interconnected, which we call worldwide sensor network (WWSN). Currently, most of the WSNs are working as isolated islands. Without sharing sensor data across different domains, the most important features of ubiquitous computing (e.g. context awareness) will not be easily achieved. For sharing among WWSN, the first nut to crack is to interconnect different WSNs which are spatially deployed in different locations with IP based Internet; the second one is to integrate them into a single WWSN over the Internet for publishing, sharing and searching of sensor data. In this paper, we present the challenge issues that should be addressed for sharing WWSN, by conducting a short survey on existing approaches.