1. Distributed Information Systems (CSCI 5533) Presentation ID: 19 Query Processing In Distributed Multi - DBMS Submitted to: Dr. Liaw, Morris Submitted by: Kumar, Manoj

2. Distributed Multi-DBMS

3. Overview of Multi-DBMS It’s a layer of software Individual Query Processor

4. Reasons for Query Processing Being complex in Multi-DBMS than in Distributed DBMS 1. Difference in Capability of Component DBMSs 2. Complexity of Cost function 3. Difficulty in Moving Data between DBMSs 4. Local Optimization capability of each DBMS may be different

5. Autonomy Issues 1. Communication Autonomy 2. Design Autonomy 3. Execution Autonomy

6. Architecture Of Distributed Multi-DBMS poses certain challenges too. Data is not only distributed across multiple sites but also across multiple databases which are individually managed.

7. Only 2 parties involve in case of Distributed DBMS –Control site –Local sites In Distributed Multi-DBMS 3 parties participate –Multi-DBMS layer at control site –Multi-DBMS layer at sites that process query –Component DBMS

8. Query Processing Layers in Distributed Multi-DBMS After Query is received at a site …. Step 1: Split the query into subqueries based on data distribution across multiple sites - Global Directory (Data Allocation Info.) - this site is CONTROL SITE

9. Step 2: Subquery is sent to the site where it needs to be processed Step 3: Multi-DBMS layer at each site further “fragments” the query Step 4: Each subquery is Translated to respective DBMS language

10. –In order to facilitate translation, Auxiliary database is used. –Auxiliary database maintains extensive information about global query language and individual query languages used by DBMSs Step 5: Query submitted to Component DBMSs are processed

11. –Decomposition –Optimization –Execution

13. Questions ??