Scalable DHT- and ontology-based information service for large-scale grids

Current grid information services are centralized or hierarchical and prove inefficient as the scale of the grid rapidly increases. The introduction of the P2P DHT technique into grids brings an encouraging path. However, current applications of the P2P DHT technique to grids do not consider the Virtual Organization (VO) management mode of grid resources. Frequent joining and leaving of resources requires strong self-organization capacity of the system to maintain the rigid structure. Moreover, arranging a moderate identifier space for a DHT ring is knotty. A large identifier space will make some nodes overloaded, while a small identifier space will bring forth the same problem as the millennium bug. In addition, current grid services are described in XML-based standards, which only support syntactic keyword and taxonomy-based queries without reasoning ability at the semantic level, leading to poor precision and integrality. To address these issues, the paper proposes a scalable DHT- and ontology-based Information Service (DIS) for a grid system, which organizes resources into a DHT ring based on the VO mode. To save the identifier space, only stable VOs can join DIS via a new DHT node, whereas volatile VOs join DIS via being the sub-domain of other VOs. Furthermore, ontology-based information integration is adopted in DIS and a novel ontology for grid resources is designed, which supports semantic-based information queries. By integrating DHT- and semantic-based query techniques, DIS speeds up the information query and improves the query precision and integrality. DIS is evaluated over the ChinaGrid environment and experimental results show that DIS provides rapid resource query, high throughput and strong scalability.