dbms⽀持哪⼏种数据模型_DBMS中不同类型的数据模型dbms⽀持哪⼏种数据模型
资料模型 (Data Model)
A data model is a model that defines in which format the data are represented and accessed. Data model mainly defines some of the data elements and relationships that exist between them.
数据模型主要定义⼀些数据元素以及它们之间存在的关系。
数据模型是定义数据以哪种格式表⽰和访问的模型。
数据模型是定义数据以哪种格式表⽰和访问的模型。 数据模型主要定义⼀些数据元素以及它们之间存在的关系。
数据模型的类型 (Types of Data Model)
There are basically two types of data model:
基本上有两种类型的数据模型：
1. Record based data model
基于记录的数据模型
2. Object based data model
基于对象的数据模型
1)基于记录的数据模型 (1) Record based data model)
When the database is organized in some fixed format of records of several than the model is called record-based data model.
当数据库以某种固定的格式组织记录时，记录模型⽐基于模型的记录模型称为基于记录的数据模型。
A fixed number of fields, or attributes in each record type and each field is usually of a fixed length. The three most popular record-based data models are,
固定数量的字段或每种记录类型和每个字段中的属性通常具有固定的长度。 三种最流⾏的基于记录的数据模型是：
(i) Relat i onal dat a m odel
(i)关系数据模型
The relational data model uses tables to represent the data and the relationships among these data. Each table has multiple columns and each column is identified by a unique name. It is a low-level model.
关系数据模型使⽤表来表⽰数据以及这些数据之间的关系。 每个表都有多个列，并且每个列都由唯⼀的名称标识。 这是⼀个低级模型。Advantages of relational data model
关系数据模型的优点
It is the simplest model at the conceptual level.
它是概念上最简单的模型。
The relational data model makes it easy to design, implement, maintain, uses the database.
关系数据模型使设计，实现，维护，使⽤数据库变得容易。
It does not affect the DBMS’s capability to access the data.
它不影响DBMS访问数据的能⼒。
The main reason for the popularity of relational model is the presence of powerful query capability.
关系模型流⾏的主要原因是强⼤的查询功能。
(i i) N et w ork dat a m odel
(i i)⽹络数据模型
In the network data model, data model data are represented by collections of records. Relationships among data are represented by links. In this data model, graph data structure is used. It permits a record to have more than one parent.
在⽹络数据模型中，数据模型数据由记录的集合表⽰。 数据之间的关系由链接表⽰。 在此数据模型中，使⽤图形数据结构。 它允许⼀个记录有多个⽗级。
Advantages of Network data model
⽹络数据模型的优势
The Network data model is also conceptually simple and easy to design.
⽹络数据模型在概念上也很容易设计。
In the network data model relationships like one-to-one and many-to-many are exist.
在⽹络数据模型中，存在⼀对⼀和多对多的关系。
In the network data model without the owner, no member exists.
在没有所有者的⽹络数据模型中，不存在成员。
In the network database terminology, a relationship is a set. Each set comprises two types of record an owner record and a member record.
在⽹络数据库术语中，关系是⼀个集合。 每组包括两种类型的记录：所有者记录和成员记录。
(i i i) Hi erarch i cal dat a m odel
(i i i)分层数据模型
In the hierarchical data, model data are represented by collections of records. Relationships among data are represented by links. In this model, tree data structure is used. There are two concepts associated with the hierarchical model segments types and parent-child relationships.
对象模型是什么在分层数据中，模型数据由记录的集合表⽰。 数据之间的关系由链接表⽰。 在此模型中，使⽤树数据结构。 有两个与层次模型段类型和⽗⼦关系相关的概念。
Advantages of Hierarchical data model
分层数据模型的优点
Since the database is based on the hierarchical structure the relationships between the various layers are logically simple.
由于数据库基于层次结构，因此各层之间的关系在逻辑上很简单。
The hierarchical data model was the first database that offered the data security that is provided by DBMS.
分层数据模型是第⼀个提供DBMS提供的数据安全性的数据库。
The Hierarchical database model is based on the parent-child relationships.
分层数据库模型基于⽗⼦关系。
It is very efficient one when the database contains a large number of one-to-many relationships.
当数据库包含⼤量的⼀对多关系时，这是⼀种⾮常有效的⽅法。
2)基于对象的数据模型 (2) Object based data model)
In the object-based data model, the database is organized in real-world objects of several types. A number of fields or attributes are defined in each object. The two most popular object-based data models are:
在基于对象的数据模型中，数据库以⼏种类型的实际对象进⾏组织。 每个对象中定义了许多字段或属性。 两种最流⾏的基于对象的数据模型是：
(i) Object ori ent ed m odel
(i)⾯向对象模型
The object-oriented model is based on a collection of objects. An object contains values stored in instances variable within the object. An object contains bodies of code that operate on the object.
⾯向对象的模型基于对象的集合。 对象包含存储在对象内的实例变量中的值。 对象包含对对象进⾏操作的代码主体。
Advantages of object oriented data model
⾯向对象数据模型的优点
It represents relationships explicitly supporting both navigated and associative access to information.
它表⽰明确⽀持导航和关联信息访问的关系。
Object-oriented database systems are not suited for all applications.
⾯向对象的数据库系统并不适合所有应⽤程序。
It is difficult to maintain when organizational information changes.
组织信息发⽣变化时很难维护。
(i i) ER (Ent i t y Relat i onal m odel)
(i i)ER(实体关系模型)
The entity relational data model based on the perception of the real world that consist of a collection of basics objects and relationships between them. It is an object-based logical model. It is also high-level data model.
实体关系数据模型基于对现实世界的感知，该模型由⼀组基础对象及其之间的关系组成。 它是⼀个基于对象的逻辑模型。 它也是⾼级数据模型。
dbms⽀持哪⼏种数据模型

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