entity-relationship model

what are the steps/phases to design a database

1st phase → understand the data usage/needs for its users

2nd phase → create the ER model for database

3rd phase → create the actual table schema (logic) and write SQL to make the table and other related features (physical, like functions, transactions, indices, etc..)

SEC

what is the 1st phase in database design

SUMMARIZE THE DATA USE CASES

what is the 2nd phase in database design

entity-relation model for the database

what is the 3rd phase in database design

create the table schema (logic) and actually write SQL to create the table and other related features (physical, like indices and transactions)

what is an entity set

a collection of similar individual objects or concepts that share the same attributes

LIKE ALL STUDENTS IN THE “student” TABLE

what is an entity

a unique object with attributes (columns)

what is an attribute domain

a set of allowed values for an attribute (column)

what are the attribute types

simple and composite

single or multi-valued

derived (like calculated from other columns)

what are composite attributes

like an attribute you get after combining multiple columns

what are the notations for ER diagrams

expanded (graph) and compact (schema text)

{var} means multi-value, var () means derived

how to choose shape for ER diagrams

rectangle = entity set (like “student”)

diamond = relationship set

double oval = multi-value attribute

dashed oval = derived attribute

underlined = primary key

what is a relationship set

basically just an entity relationship entity

what is the degree of a relationship set

the # of entities in that relationship set

what are the 4 mapping cardinalities

one-to-one (1 1)

one-to-many (1 *)

many-to-one

many-to-many

how to visualize the mapping cardinalities

line = many

arrow = 1

can relationships have attributes

yes

what are roles

specific purposes for entities

labels to lines that connect diamond to rectangle in ER diagram

what is total participation in a relationship set

every entity is in the relationship

showed by the double line

what is partial participation in a relationship set

when not every entity is in the relationship

showed by a single line