CMU15-445_1_Lecture_Note

Last updated Sep 8, 2021 Edit Source

• All
• Database

Tags: #Database

• 这门课是关于数据库的DBMS的设计和实现的, 而不是关于如何使用一个数据库的

• 2 classes per week, supplementary reading materials.

• TextBook: Database System Concepts: The best among all the textbooks - Andy Pavlo

• Project: build your own storage manager from scratch. A relatively complex software yet not a full-fledged system. Domino-way of building.

a collection of data that’s related together in some way that’s try’s to model some aspects of real world. a useful database is the one which you can ask question about it.

Flat Files:

• CSV File: Comma Separated Value File
  • 
  • If we want to find out which year the artist “Ice Cube” went solo, we could write the following python code to iterate through the file above:

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for line in file:
	record = parse(line)
	if record[0]=="Ice Cube": 
		print int(record[1])

• Implementation
  • However, there could be many issues in this way of storing information.
  • For example, this method is slow and becomes problematic when sharing data between programs(e.g. write to the same file at the same time).
• Durability Problems
• Data Integrity Problems

DBMS:

• Allows apps to store and analyze info in a database
• 不用重复造轮子
• We’ll focus on In-disk DB
• Definition, Creation, Query, Update and Administration of databases are the essential functionalities of a general-purpose DBMS.

• Early Stage Tight coupling between logical and physical layers.
  • People: Ted Codd - Purposed Relational Model

Data Model: a collection of concepts for describing the data in a database. -> The Higher Concept Schema: a description of a particular collection of data, Using a given data model. -> The Actual Plan

• There are a bunch of data models:
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Relational Model: Three Parts

• Structure: The definitions of relations and their contents.
• Integrity: Ensure the database’s contents satisfy constraints.
• Manipulation: How to access and modify a database’s contents

Relation: Definition Unordered set that contain the relation of attributes that represent entities.

• Tuple: a set of attribute values(Domains) in the relation.(所以Tuple不只是三元组哈)
• NULL可以放入任何Domain

Primary Key Uniquely identify a single tuple.

有两种:

• Procedural: 描述DBMS应该怎么找到目标数据
  • 对应 Relational Algebra ->我们这门课研究的对象
• Non-Procedural: 描述需要什么数据, 但是不给出怎么找到这些数据.
  • 对应Relational Calculus

Describe the fundamental operations to retrieve and manipulate tuples in a relation(Based on Set Algebra)

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graph LR
A([realtion1])-->B[<Some Operations>]
C([realtion2])-->B
D([...])-->B
E([realtionN])-->B
B-->F([New Relation])

关系代数是Procedural的, 描述的是筛选数据所要进行的操作. 在课件里面介绍了以上操作:

• Select

• Projection

• Union

• Intersection

• Difference

• Product

• Join

• 在课件里面举了一个例子, 如果我们用Procedural Language(比如 关系代数)来描述我们需要的数据, 那么可能会出现效率低的情况, 最佳的策略是描述我们需要的数据(Non-Procedural的), 让DBMS来决定怎样查找效率高, 这也是现在数据库里面的现行标准.(de facto standard)