首先由信息系统引入了数据库和数据库管理系统。大概讲了数据库管理系统的几个部分。接下来又引入了关系型数据库及其管理系统，介绍了关系型数据库的几个特点。还有几个概念，元组（关系）列（属性）。一个RDBMS划分了两种操作（what and how),并将后者对应用程序透明化。
数据库的结构，通常oracle database server包括database 和 database instance两部分。而打他database又包括物理和逻辑结构，instance也分为好几部分（如process，memory sructures).
人们需要存储和处理数据，就有了信息系统的诞生。An information system is a formal system for storing and processing information.数据库是一种先进的information system.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. （存储信息，为专门的应用程序处理信息提供了方式方法）。
A database management system (DBMS) is software that controls the storage,
organization, and retrieval of data（实现数据库功能的软件）. Typically, a DBMS has the following elements:
■ Kernel code
This code manages memory and storage for the DBMS.
■ Repository of metadata
This repository is usually called a data dictionary.
■ Query language
This language enables users to access the data.
A database application（数据库应用程序） is a software program that interacts with a database to access and manipulate data.
A relational database is a database that conforms to the relational model. The
relational model has the following major aspects:
Well-defined objects store or access the data of a database.
Clearly defined actions enable users to manipulate the data and structures of a
■ Integrity （完整性）rules
Integrity rules govern operations on the data and structures of a database.（完整性用来保证对数据库中数据的存储是合乎必要的规则的）。
A relational database stores data in a set of simple relations. A relation is a set of
tuples. A tuple is an unordered set of attribute values.
An RDBMS distinguishes between the following types of operations:
Logical operations(tell the database what to do)
Physical operations(the database itself how to do)
二 、方案对象（Schema Objects）
One characteristic of an RDBMS is the independence of physical data storage from
logical data structures.
a database schema is a collection of logical data structures(schema objects).a database schema is owned by a database user and has the same name as the user name.
(1)table,describes an entity,including a set of rows(a row identifies an instance of the entity).
(2)Index,increase the performance of data retrieval. Indexes are logically and physically independent of the data.
采用sql这种标准化的语言 ———Structured Query Language（SQL）
In contrast to procedural languages such as C, which describe how things should be done, SQL is nonprocedural and describes what should be done. Users specify the result that they want (for example, the names of current employees),not how to derive it.
Insert, update, and delete rows in a table
Create, replace, alter, and drop objects
Control access to the database and its objects
Guarantee database consistency and integrity
PSL/SQL and Java(the extension of sql)
A primary benefit of PL/SQL is the ability to store application logic in the database
itself. A procedure or function is a schema object that consists of a set of SQL
statements and other PL/SQL constructs, grouped together, stored in the database,and run as a unit to solve a specific problem or to perform. a set of related tasks.（procedure/function 也是 方案对象，被存储在数据库中）
事务管理的必要：oracle database is designed as a multiuser database.
Transaction：an atomic operation succeeds or fails as a whole.
（1）Data Concurrency (控制程序对数据的并行访问）
A lock is a mechanism that prevents destructive interaction between transactions accessing a shared resource. Locks help ensure data integrity while allowing maximum concurrent access to data.（在保证数据完整性的同时减少对并发访问的影响）
In Oracle Database, each user must see a consistent view of the data, including visible changes made by a user's own transactions and committed transactions of other users.
（statement-level read consistency?)
An Oracle database server consists of a database and at least one database instance. The term Oracle database is sometimes used to refer to both instance and database.
A database is a set of files, located on disk, that store data. These files can exist
independently of a database instance.
■ Database instance
An instance is a set of memory structures that manage database files. The instance
consists of a shared memory area, called the system global area (SGA), and a set
of background processes. An instance can exist independently of database files.
The database has physical structures and logical structures. Because the physical and logical structures are separate, the physical storage of data can be managed without affecting access to logical storage structures. For example, renaming a physical database file does not rename the tables whose data is stored in this file.
Database storage structure
Physical：Data files (data) controlfiles online redo log files(record changes)
Logical：Data Blocks Extents Segment(for a user object) Tablespace
Data instance structure(配图）
oracle database process
consists of client process,background process and server process(oracle process)
Instance Memory Structures
(1)SGA(System Global Area),shared memory
(2)PGA(Program Global Areas),exclusive to the processes. Background process
and server process has its own PGA.
APPLICATION AND NETWORKING ARCHITECTURE
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