Multidatabase global query optimization

Data requests to multidatabases are posed through non-procedural languages such as SQL and, for a global data request, optimization must be performed to achieve good system performance. However, the issues are often complicated in multidatabases, due to additional issues arising because of the autonomy and heterogeneity restrictions of the independent local DBMSs. The data translation problem between various local systems can be observed at the schema level and at the instance level. We have identified the need for a domain translation table in multidatabase query processing, and we discuss methods of implementing it. Some observations about multidatabase inter-site joins are made, and four methods by which multidatabase global queries can be processed are introduced and analytically compared