常见数据库系统比较 Oracle数据库
常见数据库系统比较 Oracle数据库
正在看的ORACLE教程是:常见数据库系统比较 Oracle数据库。提起数据库，第一个想到的公司，一般都会是Oracle。该公司成立于1977年，最初是一家专门开发数据库的公司。
Oracle在数据库领域一直处于领先地位。1984年，首先将关系数据库转到了桌面计算机上。然后，Oracle的下一个版本，
版本5，率先推出了分布式数据库、客户/服务器结构等崭新的概念。Oracle的版本6首创行锁定模式以及对称多处理计算机
的支持……最新的Oracle8主要增加了对象技术，成为关系-对象数据库系统。目前，ORACLE产品覆盖了大、中、小型机等
几十种机型，Oracle数据库成为世界上使用最广泛的关系数据系统之一。
Oracle关系数据库产品：
Oracle数据库产品具有以下优良特性。
（1） 兼容性
Oracle产品采用标准SQL，并经过美国国家标准技术所（NIST）测试。与IBM SQL/DS，DB2，INGRES，IDMS/R等兼容。
（2） 可移植性
Oracle的产品可运行于很宽范围的硬件与操作系统平台上。可以安装在70种以上不同的大、中、小型机上；可在VMS、
DOS、UNIX、WINDOWS等多种操作系统下工作。
（3） 可联结性
能与多种通讯网络相连，支持各种协议（TCP/IP、DECnet、LU6.2等）。
（4） 高生产率
提供了多种开发工具，能极大的方便用户进行进一步的开发。
（5） 开放性
Oracle良好的兼容性、可移植性、可连接性和高生产率是Oracle RDBMS具有良好的开放性。
ORACLE产品主要包括数据库服务器、开发工具和连接产品三类。
数据库服务器
最新版本是8，但广泛应用的是7。版本7具有以下特色：
（1）多进程、多线索的体系结构
多进程、多线索的体系结构。Oracle7包括一个到多个线索进程、多个服务器进程和多个后台进程。线索进程负责监听
用户请求，将用户请求链入内存的请求队列中，并将应答队列中的执行结果返给相应用户。服务器进程负责处理请求队列
中的用户请求，并把结果链入应答队列。线程和线索的数目都可以根据当前工作负荷动态调整。Oracle7的进程结构能充分
利用并行机上多处理机的能力，但由于其线索是用进程模拟的，由操作系统调度，这在一定程度上消弱了线索开销低的优
越性。
（2）为提高性能改进核心技术
Oracle7改进了其核心技术。其并发控制机制更加精致，包括了无限制行级封锁、无竞争查询、线索的顺序号产生机
制。在共享内存缓冲区中增加了共享的SQL Cache，提高了运行效率。
（3）高可用性
Oracle7提供了联机备份、联机恢复、镜像等多种机制保障系统具有高可用性和容错功能。
（4）SQL实现
Oracle7的SQL符合ANSI/ISO SQL 89标准。完整性约束符合ANSI/ISO标准的实体完整性和参照完整性约束。提供基于角
色的安全性。
角色是一组权限的集合。有了角色的概念，安全管理机制可翼把表或其他数据库对象上的一些权限进行组合，将它们
赋予一个角色。需要时只需将该角色授予一个用户或一组用户，这样可以降低安全机制的负担和成本。
针对集群和MPP并行计算机平台，Oracle7提供了并行服务器选件实现存盘共享。同时，Oracle7还为SMP、集群和MPP平
台提供了并行查询选件，以实现并行查询、并行数据装载等操作。
Oracle7通过分布式选件提供分布式数据库功能。其分布式选件提供了多场地的分布式查询和多场地更新功能，具有位
置透明性和场地自治性，提供全局数据库名，支持远程过程调用。
开发工具
Oracle提供的开发工具包是Developer/2000、Designer/2000、Discover/2000、Oracle Office等，它涵盖了从建模、
分析、设计到具体实现的各个环节。
Developer/2000包括：
Oracle Forms用于快速生成基于屏幕的复杂应用，具有GUI界面和多媒体功能，主要用于操纵数据和查询。
Oracle Reports是快速生成报表的工具。能生成各种复杂的报表，同样能处理多媒体信息。
Oracle Graphics用于生成各种图形应用。
Oracle Books用于生成联机文档。
Designer/2000：
这是Oracle提供的CASE工具。该工具能够帮助用户对复杂系统进行建模、分析和设计。还可以帮助用户绘制ER图、功
能分层图、数据流图和方阵图。
Discover/2000:
这是一个OLAP工具，主要用于支持数据仓库应用。它可以对历史数据进行挖掘，以找到发展趋势，对不同层次的概况
数据进行分析，以便发现有关业务的详细信息。
Oracle Office适用于办公自动化的，能完成企业范围内的消息接收与发送、日程安排、日历管理、目录管理以及拼写
检查。
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