Research Of Database Schema Meeting β-Acyclic In Fd Environment

Large scale database has been widely used in varity information systems with the development of computer and internet techology. Design and inquiry problems become the focus in database research. For acyclic database's good aspacts, and it does not have some data abnormity in cyclic database, the research of acyclic database is not only theoretical but can also give direction of database practice. There several levels of acyclicity in database.α-acyclic databse eliminates the drawbacks of cyclic database. Expectα-acyclic dababase's meritsβ-acyclic database has acyclicity of subgraph, soβ-acyclic database can effectively eliminate the abnormalty of subschemas.This paper mainly concerns the research of decomposition of a database schema meeting P3 andβ-acyclic in funcitional dependency which is without inside conflicts. Several important algorithms of relation database and acyclic database are implemented, and lots of experiments are taken based on these algorithms. The conclutions can guide the design of database directly and avoid the failure. The main contents of the dissertation are as follows.1. The research of decomposition of a database schema without inside conflict meeting PEK andα-acyclic. By analyzing the property and characteristics the minimum merge dependency set of F,the elementary merge dependency set of F is presented. The notions of weak left side conflict, weak right side conflict under elementary merge dependency set of F and PEK(join-lossless, FD and EKNF) are introduced. The scheme decomposition is discussed and the result concludes that when the elementary merge dependency set of F has weak left side conflicts or weak right side conflict, the decomposition meeting PEK isα-cyclic, laying the foundation for further investigation ofα-acyclic decomposition. On this basis, a decomposition algorithm and its correctness proof and analysis are given.2. The research of decomposition of a database schema without inside conflict meeting Ps andα-acyclic. By analyzing the property and characteristics of D( the minimum merge dependency set of F) when D has weak left side conflict or weak left side conflict, the notions of Ps(join-lossless, FD and SNF), condition T are introduced. On this basis, the necessary and sufficient condition under which a database schema without inside conflict can be decomposed into one meeting PS andα-acyclic is given. A decomposition algorithm is given accordingly with the proof for its termination, correction and analysis.3. The algorithm of calculating the extend leftside set attributes. In FD environment, extend leftside set is always involved in the discussion of several kinds of conflicts during the research of acyclic database. A polynomial time algorithm is put forward, the proof and analysis of which is given.4. The research of decomposition of a database schema without inside conflict meeting P3 andβ-acyclic. By analyzing the property and characteristics of two adjacent merge dependencies in D( the minimum merge dependency set of F) when D is without weak left side conflict and weak right side conflict, the definitions of left side set conflict, conflict between implicit sets and main merge dependency conflict are introduced. On this basis, the scheme decomposition is discussed and the result concludes that when D has weak left side conflict or weak right side conflict or left side set conflict or conflict between implicit sets or main merge dependency conflict, the decomposition meeting P3 isβ-cyclic, and the algorithm and it's analysis is presented.