数据库的三个模式 [英] The three schema of the database

问题描述

我在Access中创建了一个数据库，而且知道我必须写一个报告。
我知道数据库系统有三种形式的模式：物理，概念和外部。

执行以下ER图（使用方法 ）属于概念级别？：

或者这是否属于概念层次（包括ref完整性）：

对于phisical模式，这是否包括完整性规则？

解决方案

三级 ANSI-SPARC架构 又名三种模式方法：

• 外部架构是数据库




• 概念模式是数据库（含元数据包括约束）

通常情况下，ER图不会被认为是足够详细的外部模式或概念模式。

将这些与中的概念，逻辑和物理数据模型 混淆href =https://en.wikipedia.org/wiki/Data_modeling =nofollow>数据建模。

• 概念模型是非正式和/或不完整。例如ER图。




• 逻辑模型是正式的，在某种意义上是完全独立的。例如约为ANSI / SPARC外部或概念模式。




• 物理模型例如，大约是ANSI / SPARC内部模式。

只是多么详细和抽象的逻辑和物理模型是。或者对于这个问题，概念模型。或者这些模型如何对应于ANSI / SPARC模式。例如，任意SQL索引是内部/物理的，还是可以是用户/ DBA的外部/内部/逻辑接口的一部分。

请参阅什么是概念，逻辑和物理数据模型？及其链接概念，逻辑，物理：清除混淆。

从关系模型和ANSI / SPARC的角度来看，逻辑模型（外部和概念模式/级别）应该完全描述表及其列，约束和应用含义。但是概念 - 逻辑 - 物理表示通常反映了对关系模型的不好理解。因此，可能你的ER模型是概念 - 逻辑 - 物理模型之间的概念模型。虽然您可以将其作为逻辑模型或外部或概念模式的（部分）描述。也许你的作业本身很困惑。

你必须参考客户/教师给你的任何定义/参考。

I have created a database in Access and right know i have to write a report. I know that the databasesystem has three forms of schemas: physical, conceptual and external.

Does the following ER diagram (by using the method normalization) belongs to the conceptual level?:

Or does this belong to the conceptual level?(incl. ref integrity):

As for the phisical schema, does this include the integrity rules?

解决方案

The Three-level ANSI-SPARC Architecture aka three schema approach:

• An external schema is the database (with metadata including constraints) as seen by some user, a view of the conceptual schema.

• The conceptual schema is the database (with metatdata including constraints) per se, for an enterprise.

• The internal schema is the implementation.

Typically an ER diagram would not considered detailed enough to be an external schema or conceptual schema.

You may be confusing these with Conceptual, logical and physical data models in data modeling. (Those very wiki links are themselves confused about ANSI/SPARC.)

• A conceptual model is informal and/or incomplete. Eg an ER diagram.

• A logical model is formal and in some sense complete and implementation independent. Eg approximately an ANSI/SPARC external or conceptual schema.

• A physical model is implementation. Eg approximately an ANSI/SPARC internal schema.

However there is very little agreement about just how detailed and abstract logical and physical models are. Or for that matter conceptual models. Or how these models correspond to ANSI/SPARC schemas. Eg whether an arbitrary SQL index is internal/physical or can be part of a user's/DBA's external/internal/logical interface.

See What are Conceptual, Logical and Physical Data Models? and its link Conceptual, Logical, Physical: Clearing the Confusion.

From the point of view of the relational model and ANSI/SPARC, a logical model (external and conceptual schema/level) should completely describe tables and their columns, constraints and application meanings. But conceptual-logical-physical presentations generally reflect a poor understanding of the relational model.

So probably your ER model is a conceptual model among conceptual-logical-physical models. Although you could take it as a (partial) description of a logical model or external or conceptual schema. And maybe your assignment itself is confused.

You are going to have to refer to whatever definitions/references your client/instructor has given you for the assignment.

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