1.5. Summary

Oracle offers a broad product mix that includes not only their popular database software, but also application servers, development tools, and enterprise-level applications and services. At the heart of Oracle's product mix is the relational database model that uses tables to store application data and constraints to enforce relationships between tables and implement business rules. Examples of these constraints include Primary and Foreign Key, Not Null and Unique, and Check.

You use SQL to retrieve, add, modify, and delete data in Oracle tables. SQL statements are broadly categorized as query, DML, DDL, or DCL commands. SELECT statements are composed of the SELECT and FROM clauses and, optionally, WHERE, HAVING, and ORDER BY clauses. INSERT, UPDATE, and DELETE commands are examples of SQL DML commands. You can enter these commands directly through tools such as SQL*Plus or iSQL*Plus or through applications such as Enterprise Manager and compiled C++, COBOL, or Java programs. CREATE, ALTER, and DROP are examples of SQL DDL commands, and GRANT and REVOKE are examples of SQL DCL commands. Oracle also provides a procedural extension to SQL called PL/SQL.

Oracle uses a number of data dictionary views and dynamic performance views to provide information about the database and its contents. These contents include segments of many types, including tables, indexes, and partitions. A segment is composed of extents, which are composed of database blocks, which are composed of operating system blocks.

Extents are stored within tablespaces. A database must have at least three tablespaces, SYSTEM, SYSAUX, and TEMP, but may have many more depending on the application that it supports. Each tablespace is associated with a physical file or files on disk called a datafile. The datafiles store the data that has been inserted into application tables. Other files that make up the Oracle database include control files and redo log files.

The datafiles are accessed by the user's Server Process whenever a SQL command is issued against the database. The user's Server Process parses each SQL statement and places it into the Shared Pool component of the SGA before copying the database blocks that contain the desired data into the Database Buffer Cache component of the SGA. If the user performs a DML statement, the recovery information needed to reproduce this statement is placed in the Redo Log Buffer component of the SGA where it is ultimately written to disk by the LGWR background process. Other processes that are part of the Oracle instance include Database Writer, System Monitor, Process Monitor, and Checkpoint. The parameter initialization file (PFILE or SPFILE) is used to configure the instance.

The OFA model is useful for establishing a manageable directory structure for a new Oracle server. The OFA model recommends mount point, directory, and file-naming conventions. Once the OFA structure is established, you can use the OUI to install the Oracle 10g software into the location you've selected.