ORACLE11G started from scratch

ORACLE11G started from scratch

1.2.4. Database Mode

1. Level 3 Model

(1) Conceptual Model

The schema is a description of the logical structure of the global data in the database and a public data view for all users. It mainly describes the conceptual record types and their relationships of data, as well as some semantic constraints between data, and its description can be used in DDL definitions in DBMS.

(2) External Mode

It is also called the sub-mode or user mode. It is the logical structure and feature description of local data that can be viewed and used by database users (including application programmers and end users, it is the data view of database users and the logical representation of data related to an application.

(3) Internal Mode

Also known as storage. It is a description of the physical structure and Storage Method of Data, defining all internal record types, indexes and file organization forms, as well as data control details.

2. Secondary Image

(1) external mode/mode image

Each external mode of the database has an external mode/mode image, which defines the correspondence between the external mode and the mode, which is generally described in the external mode.

(2), mode/internal mode image

It is unique because the database only has one mode and one internal mode. It exists between the mode and the internal mode. It is the correspondence between the Global Logical Structure of data and the storage structure. It is generally described in the internal mode.

1.2.5. Data Model

It is a form framework used in databases to provide information representation and operate the tongue. It is a tool used in databases to abstract the real world.

(1) Conceptual Data Model

It is a user-oriented model for the objective world. It has nothing to do with a specific database management system and a specific computer platform.

(2) Logical Data Model

It is a database system-oriented model, which is an intermediate layer between a conceptual model and a computer.

Hierarchical Model: The tree structure is used to represent the relationship between data.

Relational Model: The relationship between data is represented by the "two tables.

Mesh Model: "Graph structure" is used to represent the relationship between data.

Object-Oriented model: "object" is used to represent the relationship between data.

(3) Physical Data Model

It is a model for computer physical representation.

Three elements of a data model: data structure, data manipulation, and integrity constraints.

1.2.6. Data integrity constraints

(1) entity integrity

If attribute A is the primary attribute of basic link R, attribute A cannot be null.

(2) integrity of reference

Defines the reference rules between the external code and the primary code.

(3) User-Defined integrity

It is a constraint for a specific relational database. It reflects the semantic requirements that must be met for the data involved in a specific application.

1.2.7 online transaction processing and online analysis processing

Online Transaction Processing (OLTP): Mainly used to process various services of the database application system. Improves work efficiency and quality

Online Analytical Processing (OLAP): OLAP enables analysts, managers, and executives to quickly, consistently, and interactively observe information from various aspects for in-depth data analysis. From the perspective of leadership and decision-making, the process comprehensively, truthfully, and intuitively reflects all aspects of camp activities.

1.2.8. Data Warehouse

Massive Data Information Storage for payment.

Features:

(1) Subject-oriented

(2) Integrity

(3) Stability

(4) Time-Varying