Are SQL Server, DB2, and Oraclereally relational?

摘要

Today, we have a huge quantity of information in the world. The development ofinformation systems makes it possible to manage our needs. Database ManagementSystems (DBMS) have played a great role in the success of information systems. Themost influential theory in DBMS is the Relational Database Model (RDM), whichwas established by E. J. Codd in the early 1970s.In this thesis, three database products, SQL Server, DB2, and Oracle are compared,which is unique because in earlier studies they have only been evaluated one databaseat a time. They are called Relational Database Management Systems (RDBMS),based on RDM. Their total market share is more than 80 % of the whole RDBMS.Codd points out important requirements for RDBMS, known as Codd’s twelve rules.The purpose of this study is to evaluate if and how closely each database vendor hasfollowed Codd’s rules when developing their products. In summary, eight of the rulesare put into practice by all of the vendors. The most difficult rules to implement are:1. modification of the view table and 2. handling of null values. Our conclusions arethat all three databases qualify as relational, and they have equal difficulties with theupdate view function and handling of null values.Key words: Database, RDM, Codd, View, Null