[ DB ] 01. R-DBMS

🖥️ R-DBMS

Database

• Organized collection of inter-related data that models some aspect of the real-world (A. Pavlo)
  • Things related are laid together; c.f., files are not like this

Database system

: Informal definition

• Magnetic tapes (storage) : Sequential access ( search )
• SSD, HDD : Random access ( search )
• File System : Store a database as comma-separated value (CSV) files ➡️ low level
  • Issue : data integrity ( 같은 Data, but 다른 내용 )
    ➡️ How to examine the validity(타당성) of the values?
  • Issue: implementation ( 여러 기능을 상황에 맞게 따로 구현? )
    ➡️ How to find a particular record? (search)
    ➡️ How to write a new application that uses the same data
  • Issue: durability ( 내구성, 연속성 )
    ➡️ What if the machine crashes while file writing?
• Database System, File system : Abstraction 역할

Database management system (DBMS)

• Software that allows applications to store and analyze information in a database
  • Access data without worrying about the file I/O-level details
• A general-purpose DBMS is designed to allow the definition, creation, querying(search), update, and administration(관리) of databases

DBMS as a data storage

• Database abstraction to avoid low-level implementation and maintenance chores
  • Store database in simple data structures
  • Access data through high-level language
• Database abstraction does not include:
  • How to implement the storage, relations, ...

DBMS as an interface

• Data definition language (DDL)
• Data manipulation language (DML)
  ➡️ Structured query language (SQL) includes both DDL and DML

---

🖥️ Relational Data Model

Data Model

: Underlying(기본) the structure of a database
: A notion for describing data or information

• Data model consists of three parts:
  • Structure
  • Operations
  • Constraints
• Examples
  • Relational data model: the most conventional ⬅️ focus
  • NoSQL ( Hadoop, MongoDB(JSON) ... )
  • Machine Learning ( Array, Matrix )
  • Misc ( hierachical, network )

Network Data Moedel

➡️ Integrated Data Storage
➡️ Linked list
➡️ Difficult to maintain
➡️ Writing queries is complex

Hierarchical Data Model

➡️ lost the data independences
➡️ duplicate data

Object-Oriented Data Model

➡️ Indefinite number of data instances ( various cnt of phone number )
➡️ There are still, but not common ( JOSN )

Relational Data Model

➡️ Effective data model
➡️ generalized method of operation ➡️ SQL

• Relational data model: A data model describes data in terms of relations (관계 측면에서)
• Relation
  • An unordered set that contains the relationship of attributes that represent entities ➡️ order does not matter

Relation (Table)

• Attribute (column) = feature = variable
  • Attribute values are required to be atomic (indivisible data type)
    - Atomic data type : int, float, string ... ↔️ cf. class, structure
  • The set of allowed values for each attribute is called the domain (possible value range) of the attribute
  • NULL is a member of every domain, indicating that the value is “unknown” ➡️ misssing or N/A
• Tuple (row) = record = data instance(point)
  • A tuple is a set of attribute values (also known as its domain) in the relation
  • Each tuple has one value for each attribute of the relation
  • Values are (normally) atomic/scalar

➡️ Schema ( Header ) : Structure of table, List of attributes and their types

Notation

• Using a table
• Using a set notation
  • Structure: instructor(ID, name, dept_name, salary)
  • Tuples: (76766, Crick, Biology, 72000.00),
    (83821, Brandt, Comp. Sci., 92000.00),
    (45565, Katz, Comp. Sci., 75000.00)
  • Ordered sets ➡️ attributes in a tuple : order does matter
    Ex_ (76766, Crick, Biology, 72000.00) != (72000.00, Biology, Crick, 76766)

Keys

• Key : Identifier for records within a relation
  • One type of constraints (unique)
  • One or more attributes form a key
  • A key for a relation ➡️ do NOT allow duplicates of the same values of the key attributes

Primary Keys

• A relation’s primary key uniquely identifies a single tuple
• instructor(ID, name, dept_name, salary)

Foreign Keys

• A foreign key specifies that an attribute from one relation has to map to a tuple in another relation
  • Value in one relation must appear in another relation
    - Referencing relation ➡️ Referenced relation

Data Language

• Data definition language (DDL)
  • How to represent relations and information in a database
    - Defines database schemas
• Data manipulation language (DML)
  • How to store and retrieve information from a database
  • Procedural
    - The query specifies the (high-level) strategy the DBMS should use to find the desired results
    - Based on relational algebra

Database Schema

• Database: a collection of relations (tables)
• Database schema: the logical structure of the database
• Database instance: a snapshot of the data in the database at a given instant in time
  • Relation instance: a snapshot of a relation (attributes and tuples) at a given instant in time

HGU 전산전자공학부 홍참길 교수님의 23-1 Database System 수업을 듣고 작성한 포스트이며, 첨부한 모든 사진은 교수님 수업 PPT의 사진 원본에 필기를 한 수정본입니다.