设为首页 加入收藏

TOP

E.F Codd提出的365bet是哪的网站_365bet手机官网_365bet提现流程设计12条准则
2011-05-12 15:37:16 来源: 作者: 【 】 浏览:35492次 评论:0
Dr.?E.F.?Codd,?an?IBM?researcher,?first?developed?the?relational?data?model?in?1970.?In?1985,?Dr.?Codd?published?a?list?of?12?rules?that?concisely?define?an?ideal?relational?database,?which?have?provided?a?guideline?for?the?design?of?all?relational?database?systems?ever?since.

I?use?the?term?"guideline"?because,?to?date,?no?commercial?relational?database?system?fully?conforms?to?all?12?rules.?They?do?represent?the?relational?ideal,?though.?For?a?few?years,?scorecards?were?kept?that?rated?each?commercial?product’s?conformity?to?Codd’s?rules.?Today,?the?rules?are?not?talked?about?as?much?but?remain?a?goal?for?relational?database?design.

Following?is?a?list?of?Codd’s?12?rules,?including?his?original?name?for?each?rule?and?a?simplified?description.?I?also?have?included?a?note?where?certain?rules?are?problematic?to?implement.?Don’t?worry?if?some?of?these?items?are?confusing?to?you,?as?we?move?further?through?this?newsletter?series?we?will?fill?in?the?details.

以下这12条规则的中文由?SilentKiller?翻译,不保证全部正确。

Rule?1:?The?Information?Rule
All?data?should?be?presented?to?the?user?in?table?form.?Last?week’s?newsletter?already?discussed?the?basics?of?this?rule.
1,信息准则
关系365bet是哪的网站_365bet手机官网_365bet提现流程中的所有信息都应在逻辑层上用表中的值显式的表示。

Rule?2:?Guaranteed?Access?Rule
All?data?should?be?accessible?without?ambiguity.?This?can?be?accomplished?through?a?combination?of?the?table?name,?primary?key,?and?column?name.
2,保证访问准则
依于表名,主键和列名,保证能以逻辑方式访问365bet是哪的网站_365bet手机官网_365bet提现流程中的每个数据项。

Rule?3:?Systematic?Treatment?of?Null?Values
A?field?should?be?allowed?to?remain?empty.?This?involves?the?support?of?a?null?value,?which?is?distinct?from?an?empty?string?or?a?number?with?a?value?of?zero.?Of?course,?this?can’t?apply?to?primary?keys.?In?addition,?most?database?implementations?support?the?concept?of?a?nun-?null?field?constraint?that?prevents?null?values?in?a?specific?table?column.
3,空值的系统化处理
RDBMS支持空值(不同于空的字符串或空白字符串,并且不为0)系统化的
表示缺少的信息,且与数据类型无关。

Rule?4:?Dynamic?On-Line?Catalog?Based?on?the?Relational?Model?A?relational?database?must?provide?access?to?its?structure?through?the?same?tools?that?are?used?to?access?the?data.?This?is?usually?accomplished?by?storing?the?structure?definition?within?special?system?tables.
4,基于关系模型的联机目录
365bet是哪的网站_365bet手机官网_365bet提现流程的描述在逻辑上应该和一般数据采用同样的方式,使得授权用户可以
使用查询一般数据所用的关系语言来查询365bet是哪的网站_365bet手机官网_365bet提现流程的描述信息。

Rule?5:?Comprehensive?Data?Sublanguage?Rule
The?database?must?support?at?least?one?clearly?defined?language?that?includes?functionality?for?data?definition,?data?manipulation,?data?integrity,?and?database?transaction?control.?All?commercial?relational?databases?use?forms?of?the?standard?SQL?(Structured?Query?Language)?as?their?supported?comprehensive?language.
5,合理广泛的子语言准则
一个关系系统可以具有几种语言和多种终端使用方式(表格填空方式,命令
方式等)。但是必须有一种语言,它的语句可以表示为具有严格语法规定的
字符串,并能全面的支持以下功能:数据定义,视图定义,数据操作,完整约束
,授权,事物控制。

Rule?6:?View?Updating?Rule
Data?can?be?presented?to?the?user?in?different?logical?combinations,?called?views.?Each?view?should?support?the?same?full?range?of?data?manipulation?that?direct-access?to?a?table?has?available.?In?practice,?providing?update?and?delete?access?to?logical?views?is?difficult?and?is?not?fully?supported?by?any?current?database.
6,视图更新准则
所有理论上可更新的视图也应该允许由系统更新。

Rule?7:?High-level?Insert,?Update,?and?Delete
Data?can?be?retrieved?from?a?relational?database?in?sets?constructed?of?data?from?multiple?rows?and/or?multiple?tables.?This?rule?states?that?insert,?update,?and?delete?operations?should?be?supported?for?any?retrievable?set?rather?than?just?for?a?single?row?in?a?single?table.
7,高阶的插入,更新和删除
把一个基本关系或导出关系作为一个操作对象进行数据的检索以及插入,更新和删除。

Rule?8:?Physical?Data?Independence
The?user?is?isolated?from?the?physical?method?of?storing?and?retrieving?information?from?the?database.?Changes?can?be?made?to?the?underlying?architecture?(?hardware,?disk?storage?methods?)?without?affecting?how?the?user?accesses?it.
8,数据的物理独立性
无论365bet是哪的网站_365bet手机官网_365bet提现流程的数据在存储表示上或存取方法上做任何变化,应用程序和终端活动要都保持逻辑上的不变性。

Rule?9:?Logical?Data?Independence
How?a?user?views?data?should?not?change?when?the?logical?structure?(tables?structure)?of?the?database?changes.?This?rule?is?particularly?difficult?to?satisfy.?Most?databases?rely?on?strong?ties?between?the?user?view?of?the?data?and?the?actual?structure?of?the?underlying?tables.
9,数据的逻辑独立性
当基本表中进行理论上信息不受损害的任何变化时,应用程序和终端和终端活动都要保持逻辑上的不变性。

Rule?10:?Integrity?Independence
The?database?language?(like?SQL)?should?support?constraints?on?user?input?that?maintain?database?integrity.?This?rule?is?not?fully?implemented?by?most?major?vendors.?At?a?minimum,?all?databases?do?preserve?two?constraints?through?SQL.?No?component?of?a?primary?key?can?have?a?null?value.?(see?rule?3)?If?a?foreign?key?is?defined?in?one?table,?any?value?in?it?must?exist?as?a?primary?key?in?another?table.
10,数据完整的独立性
关系365bet是哪的网站_365bet手机官网_365bet提现流程的完整性约束必须是用数据子语言定义并存贮在目录中的,而不是在应用程序中加以定义的。至少要支持以下两种约束:实体完整性:主键中的属性不允许为NULL?;?参照完整性:对于关系365bet是哪的网站_365bet手机官网_365bet提现流程中每个不同的非空的外码值,必须存在一个取自同一个域匹配的主键值。

Rule?11:?Distribution?Independence
A?user?should?be?totally?unaware?of?whether?or?not?the?database?is?distributed?(whether?parts?of?the?database?exist?in?multiple?locations).?A?variety?of?reasons?make?this?rule?difficult?to?implement;?I?will?spend?time?addressing?these?reasons?when?we?discuss?distributed?databases.
11,分布的独立性
一个RDBMS应该具有分布独立性。用户不必了解365bet是哪的网站_365bet手机官网_365bet提现流程是否是分布式的。(无论365bet是哪的网站_365bet手机官网_365bet提现流程是否有部分处于复杂多重环境中)

Rule?12:?Nonsubversion?Rule
There?should?be?no?way?to?modify?the?database?structure?other?than?through?the?multiple?row?database?language?(like?SQL).
12,无破坏准则
若RDBMS有某种低级语言,这一低级语言不能违背或绕过完整性准则以及高级关系
语言表达的约束。

Most?databases?today?support?administrative?tools?that?allow?some?direct?manipulation?of?the?datastructure.

Over?the?life?of?this?newsletter,?I?will?be?expanding?on?the?concepts?covered?by?each?of?Codd’s?rules.?I?will?use?the

relational?query?language?of?choice,?SQL,?to?illustrate?these?concepts?and?explain?relational?database?structure?in?detail.??
Tags:设计 责任编辑:admin
】【打印繁体】【投稿】【收藏】 【推荐】【举报】【评论】 【关闭】 【返回顶部
上一篇最新翻译书籍《物理365bet是哪的网站_365bet手机官网_365bet提现流程设计—.. 下一篇OLTP 应用程序的 DB2 调优技巧

最新文章

热门文章

推荐文章

相关文章