The Research Of Schema Evolution Strategy With Minimum Query Cost

Schema evolution is one of the important researches in database researches. How to ensure that the new schema is the optimal schema of the current application and how to keep integrity and consistency after schema evolution are two important problems in schema evolution.This paper makes a detailed analysis on the relevant research of schema evolution, in allusion to the shortcomings of the existing schema evolution methods, this paper put forward a schema evolution model based on the mapping. In view of multiple candidate schemas, this paper put forward a schema select model. Through the schema select model, we can choose the optimal schema that meets the current application requirements from all of the candidate schemas, and the new schema has the minimum query cost. The model simplifies the candidate schema selection into the string process. Through the string processing to get the target schema, this paper simplifies the complex calculations of candidate schema selection, and don’t need database administrators to analyze the current database.In the schema evolution based on mapping, we built schema mapping based on attributes, show integrity by mapping and keep the data consistency between the new schema and the original schema. When the original schema or new schema change schema, we put forward the schema mapping adjust-algorithm, and keep the correctness and consistency of the mapping between the new schema and the original schema. In order to provide operations for the original schema, we put forward a decomposition algorithm to change the operation of original schema into the operation of the new schema.Experimental results show that the schema select model can choose the optimal schema according to the current situation of the database application, and the schema evolution model can deal with query operation of the original schema by changing the query operation of original schema into the query operation of the new schema.