Part5UNIT3AFundamentalsoftheDatabaseSystem.doc

Part5 UNIT3 A Fundamentals of the Database System UNIT 3 A Fundamentals of the Database System Grasping the Concept of a Database A database is a collection of information—preferably related information and preferably organized. A database consists of the physical files you set up on a computer when installing the database software. On the other hand, a database model is more of a concept than a physical object and is used to create the tables in your database. This section examines the database, not the database model. By definition, a database is a structured object. It can be a pile of papers, but most likely in the modern world it exists on a computer system. That structured object consists of data and metadata, with metadata being the structured part. Data in a database is the actual stored descriptive information, such as all the names and addresses of your customers. Metadata describes the structure applied by the database to the customer data. In other words,the metadata is the customer table definiton. The customer table definition contains the fields for the names and addresses, the lengths of each of those fields, and datatypes. (A datatype restricts values in fields, such as allowing only a date, or a number). Metadata applies structure and organization to raw data. Fig.5-3A-1 shows a general overview of a database. A database is often represented graphically by a cylindrical disk, as shown on the left of the diagram. The database contains both metadata and raw data. The database itself is stored and executed on a database server computer. In Fig.5-3A-1, the database server computer is connected across a network to end-users running reports, and online browser users browsing your Web site (among many other application types). There are numerous, precise explanations as to what exactly a database model or data model is. A database model can be loosely used to describe an organized and ordered set of information stored on a computer. This ordered set of da