quartz/content/notes/13-databases-1.md

title	aliases	tags
13-databases-1		cosc203 lecture

What is a database

• an integrated collection of data
• implicit properties
  • represents some aspect of th real world, called miniworld
  • is a coherent collection of data with inherent meaning
  • is designed built and populated with data for a specific purpose

DBMS

• a software system designed to store, manage, and facilitate access to the database
• Oracle, SQL erver, MySQL, MonogDB

Application program

• a program that provides access to the dtabase by sending queries and requests for data to the DBMS

This course

• modelling and design of DBs
• programming (SQL + appliation development)
• DBMS implementation

specifiically relational databases

• ER modelling
• datbase normalisation
• SQL

relational vs nosql

relation is better for structured data, nosql is better for abstract data, as it is more flexible

Data modelling

first step in designing database

• create a data model for a specific problem domain

a model is Defn: a collection of concepts that can be used to describe the structure of a database such as data types, relationsips, and contraints that should hold for the data

schema Defn: a collection of metadata that describes the logical view of a database

noSQL databases are either schema-free or have relaxed schemas

conceptual data modelling

model the data close to the way the users percieve the data

ER model

• popular high level conceptual model
• uses diagrammatic notations - er diagram (ERD)

three notations

• chens notation
• crows foot notation
• UML notation

Example

how to model

entities

• a thing in the real world with independent existence
  • physical existence
  • conceptial existence

entity type is a collection of entities with the same attributes — represented by a rectangle

attribute

• a property of an entity
  • simple (atomic) e.g, first name
  • composite (can be divided) e.g., address
  • single value e.g., id number
  • multi value e.g., siblings
  • stored - by default
  • derived - drawn as dashed ovals e.g., age is derived from birth date
  • key
    • unique
    • simple or composite
    • underlined in ERD

relationships

a relationship model the connection between entitiy types

e.g., each employee works for one department

relationship type is a set of relationsihps among entities from the particular entity types - represented by diamonds

relationship types can have attributes

properties

• degree
  • binary binary relationship|200
  • n-ary n-ary relationship|300
• cardinality for binary relationships
  • one to one
  • one to n
  • m to n
• participation
  • total participation
    • marked by double line
    • relationship is required
  • partial
    • marked by single line
    • relationsihp is not required

weak entities

• regular tyupes