What are the types of databases?

What types of databases are there?

Databases are usually divided into:

There are three types of hierarchical databases, network databases and relational databases.

Different databases are related and organized according to different data structures.

The database is divided into types according to the data model, including hierarchical model, network model and relational model.

1. Hierarchical model:

The hierarchical model uses a tree structure to represent record types and their relationships.

The basic characteristics of the tree structure are:

1. There is only one node with no parent node;

2. Other nodes have and have a parent node.

In the hierarchical model, the nodes of the tree are record types. The relationship between the upper layer record type and the next layer record type is 1:n.

The hierarchical model is like the inverted tree we give below.

Note: To search for records in a hierarchical database, the access path must be specified. This relational model does not support m:n relationships.

2. Mesh model:

The connections between nodes in the mesh model are not restricted by hierarchy and can be connected at will, so its structure is a connected graph of nodes.

The characteristics of the mesh model structure are:

1. There is more than one node with no parent node;

2. At least one node has more than one parent node.

Note: Although the network model can reflect various complex relationships, in terms of specific implementation, the network model only supports 1:n contact, so

The m:n contact can be converted into a 1:n contact.

3. Relationship model:

The essence of the relational model is to use several two-dimensional tables to represent entities and their relationships.

Relationships are defined through relationship names and attribute names. A relationship can be formally expressed as:

R(A1,A2,A3,…,Ai,…)

Where: R is the relationship name, Ai is the attribute name of the relationship.

Currently commonly used database management systems include:

ACCESS, SQL Server, Oracle, MySQL, FoxPro and Sybase, etc.

ACCESS is a microcomputer database management system launched by Microsoft Corporation in the United States in 1994. It has the characteristics of friendly interface, easy to learn and use, simple development, and flexible interface. It is a typical new generation desktop database management system.

Oracle is the world's largest information management software and service provider. It was founded in 1977 and is headquartered in Redwood Shores, California, USA. The complete e-commerce products and services provided by Oracle include: Used to build and deliver Web-based Internet platforms; Comprehensive and comprehensive business applications with Internet capabilities; Powerful professional services to help users implement e-commerce strategies, as well as design and customization and implement various e-commerce solutions...

SQL is the abbreviation of English Structured Query Language, which means structured query language. The main function of SQL language is to establish contact and communicate with various databases. According to ANSI (American National Standards Institute), SQL is used as the standard language for relational database management systems. SQL statements can be used to perform a variety of operations, such as updating data in the database, extracting data from the database, etc. Currently, the vast majority of popular ones are relational database management systems.

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Basic types of database

The database is divided into types according to the data model, including hierarchical model, network model and relational model. Below we study the following three models respectively.

Hierarchical model

The hierarchical model uses a tree structure to represent record types and their relationships.

The basic characteristics of the tree structure are:

1. There is only one node with no parent node;

2. Other nodes have and have a parent node.

In the hierarchical model, the nodes of the tree are record types. The relationship between the upper layer record type and the next layer record type is 1:n.

The hierarchical model is like the inverted tree we give below.

Note: To search for records in a hierarchical database, the access path must be specified. This relational model does not support m:n relationships.

Mesh model

The connections between nodes in the mesh model are not restricted by hierarchy and can be connected at will, so its structure is a connected graph of nodes.

The characteristics of the mesh model structure are:

1. There is more than one node with no parent node;

2. At least one node has more than one parent node.

Note: Although the network model can reflect various complex relationships, in terms of specific implementation, the network model only supports 1:n contact, so

The m:n contact can be converted into a 1:n contact.

Relationship model

The essence of the relational model is to use several two-dimensional tables to represent entities and their relationships.

Relationships are defined through relationship names and attribute names. A relationship can be formally expressed as:

R(A1,A2,A3,…,Ai,…)

Where: R is the relationship name, Ai is the attribute name of the relationship.

We won’t study too much about this here. We will study it in detail in future chapters.

Excuse me: What types of databases are there?

At present, databases can be divided into three categories according to their structure:

1. Hierarchical type

2. Mesh type

3. Relational type

Currently, most integrated development environments (including languages) can be used to process databases, and there are too many to mention. As far as relational DBMS is concerned, I think:

Representatives of small and medium-sized enterprises include Access and FoxBASE

Medium-sized representatives include VFP, dBASE, and PB

Large-scale representatives include oracle and SQL

Just tell me what you want to learn, it will definitely be more promising and difficult. Nowadays, the most popular database on the market is Oracle. Currently, the salary of DBA in database is relatively high in all aspects. When it comes to learning Oracle, we can't help but mention that its certifications include OCA, OCP, and OCM. Those who are mainly engaged in Oracle will take this certification. The gold content of OCA is relatively low, so I don't mind taking this test. Instead of taking the OCP directly, OCP is relatively big, but as long as you attend a training institution authorized by Oracle, there will be no problem.

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