DDI复习

Relation=Table=Entity

Relationship是Relation之间的关系

所有有关系的Relations（Entity）的集合即Entity Set Attribute即Colum

Domain为Attribute的所有可能值集合 Tuple即Row

Entity：nColums+nRows=nAttributes+nTuple另作Degree N and Cardinality N

UML=Unified Modeling Language DBMS=Database Management System relational schema Example:

Employee{Emp_Ref#, FirstName, LastName, Phone, Dept_Ref}

Primary key (PK)表内检索用

Composite key联合键，多个Attributes，每项为Key Attribute Candidate key候选Key没当做用到的Key Null的问题1数据不全2不能在主键出现3应该避免 Foreign key (FK)相关PK的Table System catalog=The Data Dictionary

Optional participation“O”“O..1” Mandatory participation“1..1”

Unary/recursive relationship（Entity中Relationship） Binary relationship（2Entity中Relationship） Ternary relationship（多Entity中Relationship） obligatory relationships绝对一对一 obligatory on one side一对多 non-obligatory多对多

junction table=Associative Entity / Composite Entity / Bridge Entity Weak entity从属Table

identifying relationship链接Weak Entity与Parent Entity

Primary Key（uniquely identify、Attribute or combination of attributes、Guarantee entity integrity）

Composite Primary Keys（联合主键） surrogate key（） Relational algebra Union两个表の并集 Intersect两表の交集

Cartesian product=R1 X R2（Yields all possible pairs of rows from two tables）

Division两Tuple间相同元素对应下一Tuple的相同元素 各种Join

Structured Query Language (SQL)

SQL Constraints（NOT NULL、UNIQUE、DEFAULT、CHECK） SELECT建立查询表的第一句

Alias–“SELECT A*B AS TOTRESULT”? TOTRESULT为 Alias Aggregate Functions： Like? COUNT; AVG; MIN; MAX; SUM Special Operators: “LIKE, BETWEEN, IN, EXIST”

HTML: - Hyper Text Markup Language (静态)

? ? ? ? ? ?

- beginning and end of a paragraph - beginning and end of bold fonts - beginning and end of italic fonts

- beginning and end of a table - beginning and end of a row - beginning and end of a cell

XAMPP：Free software package with the following components

? Web server: Apache

? Server-side programming languages: PHP and Pearl ? Database: MySQL

XML (Extensible Markup Language) is a metalanguage for creating custom markup languages

? XML is useful in integrating data from different databases:

? Data are first converted from its native format into XML data

in a unified format

? Then write the XML data to a relational database

本文来源：https://www.bwwdw.com/article/uv1h.html