Chapter One Introduction

Data : Symbolic records describing things
Database : Long-term storage in the computer, organized, shareable data collection

With less redundancy, higher data independence and easy scalability, and can be shared by users
Database management system : a management software
Database system : consists of databases, database management systems, application systems, database administrators, and users

Database Administrator (DBA)

Manual management stage : data is not independent, redundant, and not shared
File system stage : poor independence, poor sharing, and high redundancy
Database system stage : structured, good sharing, low redundancy, good independence

Substance : things that exist objectively and can be distinguished from each other
Attribute : a certain characteristic of the entity
Code : the attribute set that uniquely identifies the entity
Domain : The value range of the attribute is called the domain of the attribute
Entity type : Use a collection of entity names and their attribute names to abstractly describe similar entities
Entity set : a collection of entities of the same type
Contact : one to one, one to many, many to many

ER

Substance-rectangle

Attribute-ellipse

Contact-Diamond

Hierarchical model -tree structure
Mesh data model
Relational data model -tables and tables

Relational integrity constraints (entity integrity, referential integrity, user-defined integrity)

Mode (logical mode) : the description of the logical structure and characteristics of all data in the database, which is a common data view for all users

A database has only one mode
External mode (submode/user mode) : It is the description of the logical structure and characteristics of the local data that the database user sees and uses, and is the data view of the database user

A database can have multiple external modes
Internal mode (storage mode) : is the description of the physical structure of the data and the storage structure

A database has only one internal schema

For each external mode, the database system has an external mode/mode image

Mode/intra mode image is unique

Chapter 2 Relational Database

Candidate code : If the value of a certain attribute group in the relationship can uniquely identify a tuple, and its proper subset is not enough, then the attribute group is a candidate code
Main code : Choose one of the candidate codes as the main code
Primary attributes : the attributes of the candidate code become attributes
Non-code attributes : attributes not included in any candidate codes
Relationship mode : R(U,D,DOM,F)
- R: Relationship name
- U: The set of attribute names that make up the relationship
- D: The domain from which the attribute in U comes from
- DOM: a collection of attributes to domain mapping
- F: A collection of data dependencies between attributes

Entity integrity : all main attributes cannot take null values, not just the main code attributes
Referential integrity : foreign code correspondence
User-defined integrity : constraints on a certain attribute

Start with BEGIN TRANSACTION and end with COMMIT or ROLLBACK

ACID

Atomicity (atomicity): indivisible, the operations in a transaction are either done or not done
Consistency: From one consistency state to another consistency state
Isolation (isolation): the execution of one thing cannot be interfered by another transaction
Durability: Once a thing is submitted, its changes to the database data should be permanent