This chapter provides an overview of Oracle Database.
This chapter contains the following topics:
- About Relational Databases
- Schema Objects
- Data Access
- Transaction Management
- Oracle Database Architecture
- Oracle Database Documentation Roadmap
About Relational Databases
Every organization has information that it must store and manage to meet its requirements. For example, a corporation must collect and maintain human resources records for its employees. This information must be available to those who need it.
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An information system is a formal system for storing and processing information. An information system could be a set of cardboard boxes containing manila folders along with rules for how to store and retrieve the folders. However, most companies today use a database to automate their information systems. A database is an organized collection of information treated as a unit. The purpose of a database is to collect, store, and retrieve related information for use by database applications.
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Database Management System (DBMS)
A database management system (DBMS) is software that controls the storage, organization, and retrieval of data.
Typically, a DBMS has the following elements:
- Kernel codeThis code manages memory and storage for the DBMS.
- Repository of metadataThis repository is usually called a data dictionary.
- Query languageThis language enables applications to access the data.
A database application is a software program that interacts with a database to access and manipulate data.
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The first generation of database management systems included the following types:
- HierarchicalA hierarchical database organizes data in a tree structure. Each parent record has one or more child records, similar to the structure of a file system.
- NetworkA network database is similar to a hierarchical database, except records have a many-to-many rather than a one-to-many relationship.
The preceding database management systems stored data in rigid, predetermined relationships. Because no data definition language existed, changing the structure of the data was difficult. Also, these systems lacked a simple query language, which hindered application development.
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