Research on Deciding a Database Schema Without Inside Conflicts Meeting P\-3 and β-Acyclicity

The α-acyclic database eliminates several good properties such as the join dependency of R is equivalent to a set of multivalued dependencies and every pairwise consistent database over R is globally consistent. The α-acyclic database mainly concerns the acyclicity of global database schema, but there still exists cycles in subschemas. Expect α-acyclic databases merits β-acyclic database has acyclicity of subgraph, so β-acyclic database can effectively eliminate the abnormality of subschemas. Being a kind of important acyclic levels, the property of β-acyclicity has become basic demand in normalization with lossless join, keeping dependency and 3NF under FD environment. 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 P\-3 is β-cyclic, and the algorithm and its analysis is presented, laying down the foundation for further investigation of β-acyclic decomposition.