Chapter 1: Introduction¶

1. Three Aspects to study Database¶

1.Modeling and design of databases.
- Get (abstract) data models from real world, then translate them into the forms suitable for the target DBMS (Database Management System) - tables, views.
2.Programming: use database
- queries and update of data.
3.DBMS implementation
- how does DBMS work, and how to design a DBMS.

两种访问数据库的方法

A collection of interrelated data, relevant to an enterprise.
A large collection of integrated and persistent data (DB). [R. Ramakrishnan, J. Gehrhe]
A collection of information that exists over a long period of time, often many years. [Ullman]
长期存储在计算机内、有组织的、可共享的数据集合。[萨师煊，王珊]

( Database ) + A set of programs used to access, update and manage the data in database.

Major properties of DBMS

Efficiency and scalability (可扩展性) in data access; Reduced application development time;
Data independence (physical data independence / logical data independence);
Data integrity (完整性) and security;
Concurrent access and robustness (recovery).

File processing system (1950s-1960s)
Network and hierarchical DBMS (1960s-1970s)
- 网状数据模型、层次数据模型 - 网状数据库、层次数据库 (结构复杂、使用很困难)
Relational database systems (RDBMS)
- Relational model (1970, E.F. Codd)
- Relational database system developed (late 1970s)
- Relational database systems on the market (1980s)
- Matured relational DBMS technology (1990s)

Object-oriented database system (OODBMS)
Object-relational database systems (ORDBMS)
Application-oriented database systems
- Spatial, temporal, multimedia, Web databases
Data Warehousing (数据仓库), Online Analytical Processing (联机分析处理), and Data Mining (数据挖掘) systems (for data analysis)

How to use DB - Different usage needs different level of abstraction. (e.g., student score management system)

Physical level: describes how a record is stored. Files
Logical level: describes data stored in database, and the relationships among the data on upper level.
View level: application programs hide details of data types. Views can also hide information (e.g., employee’s salary) for security purposes.

Similar to types and variables in programming languages ( type ↔ schema, variable ↔ instance)
Schema - the structure of the database on different level
- Analogous to type information of a variable in a program
- Physical schema: database design of structure at the physical level
- Logical schema: database design of structure at the logical level
- Subschema: schema at view level
Instance - the actual content of the database at a particular point in time
- Analogous to the value of a variable

Data model is a collection of conceptual tools for describing:
- data structure
- data relationships
- data semantics
- data constraints
Different data models:
- Entity-Relationship model
- Relational model
- Other models

Steps of Database Design

Requirement analysis
- What data, applications, and operations needed
Conceptual database design
- A high-level description of data, constraints using E - R model or a similar high level data model
Logical database design:
- Convert the conceptual design into a DB schema
Schema refinement
- Normalization of relations: Check relational schema for redundancies and related anomalies.
Physical database design : Indexing, clustering and database tuning
Create and initialize the database & Security design Load initial data, testing Identify different user groups and their roles

The diagram is below:

Let's show an example:

From the diagram we can understand the meaning of schema, attribute, column and tuple.

Database Language:

SQL

SQL has been widely used

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SELECT customer-name
FROM customer
WHERE customer-id = '192-83-7465'