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CHAPTER 4 RELATIONAL DATABASES INTRODUCTION Questions to be addressed in this chapter: How are databases different than file-based legacy systems? Why are databases important and what is their advantage? What is the difference between logical and physical views of a database? What are the fundamental concepts of database systems such as DBMS, schemas, the data dictionary, and DBMS languages? What is a relational database, and how does it organize data? How are tables structured to properly store data in a relational database? Relational databases underlie most modern integrated AISs. They are the most popular type of database used for transaction processing. FILES VS. DATABASES There are some basic principles about how data are stored in computer systems. An entity is anything about which the organization wishes to store data. At a college or university, one entity would be the student. Information about the attributes of an entity (e.g., the student’s ID number and birth date) are stored in fields . All the fields containing data about one entity (e.g., one student) form a record . A set of all related records forms a file (e.g., the student file). A set of interrelated, centrally coordinated files forms a database . Database systems were developed to address the problems associated with the proliferation of master files. For years, each time a new information need arose, companies created new files and programs. This practice resulted in a significant increase in the number of master files. This proliferation of master files created several problems. Often the same information was stored in multiple master files. It was difficult to effectively integrate data and obtain an organization-wide view of the data. Also, the same information may not have been consistent between files. If a student changed his phone number, it may have been updated in one master file but not another. The database approach treats data as an organizational resource that should be used by and managed for the entire organization, not just a particular department. A database management system (DBMS) serves as the interface between the database and the various application programs. The combination of the database, the DBMS, and the application programs that access the database is referred to as the database system . The person responsible for the database is the database administrator . As technology improves, many large companies are developing very large databases called data warehouses. Database technology is everywhere. Most new AISs implement a database approach. Virtually all mainframe computer sites use database technology. Use of databases with PCs is growing also. Accountants are likely to audit or work for companies that use database technology to store,
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