A Hierarchical Export/Import Scheme for Data Sharing in a Federated Distributed Database System
Hyunchul Kang, Sang Hyuk Son · Database Systems for Advanced Applications · 1991
When a data object is shared in a federated distributed database system (FDDBS), the exporter is responsible to refresh data of all importers. This causes the bottleneck phenomenon at the exporter’s site due to all importers competing for its refresh service. In this paper, we propose an efficient export/import scheme for data sharing in a FDDBS that can solve this problem. We devise the procedures for the exporter to update its copy, and for the importers to access their copies, and the negotiation protocol for data exporting/importing between two databases in the federation. We introduce the concept of the cost of data exporting, and derive equations to quantify it. Knowing this cost helps each database decide in negotiation whether it can export data further or not. Experimentaion results show that using our scheme, the bottleneck phenomenon at the exporter’s site can be eliminated at the penalty of incurring more data transmition in the federation than using a simple export/import scheme that suffers from the bottleneck problem, but they also show that this penalty is not severe. 1. Intloductlon The conventional approach to integrating multiple databases each of which was independently designed and managed is to integrate their database schemata towards a global schema and to define mappings between the global schema and each of the local schemata. The user queries and/or transactions are specified against the global schema and translated to be executed against the relevant local databases. This approach provides users with physically distributed but logically centralized view of the integrated database system. Users lose the control over their local databases. They should conform to the global view of the database. An alternative approach to database integration employs a federated architecture [HM85]. A federated distributed database system (FDDBS) provides users with not only physically but DATABASE SYSTEMS FOR ADVANCED APPLICATIONS ‘91