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Chapter 3

MIST 4610 Chapter Notes - Chapter 3: Relational Algebra, Foreign Key, Discrete Element Method

Management Information Systems
Course Code
MIST 4610

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Chapter 3- The Single Entity
Relation: 2 dimensional table arranged in rows and columns
Relational database: collection of relations, where relation is a
mathematical term for a table
o All rows in a table store data about the same type of item
Primary key: an identifier so that a particular row can be
The tables in a relational database are connected or related by
means of the data in the tables
o Connection is through a pair of values- a primary key and a
foreign key
Relational model supports set processing (multiple records-at-a-
time) which is implemented as Structured Query
Data independence: relational model separates the logical design
of a database from its physical storage
Represent an entity by a rectangle
o Entity has characteristics/attributes
Attribute: discrete element of data; is not usually broken
down into smaller components; identifies data we want to
Instance: particular occurrence of an entity
Identifier: an attribute or collection of attributes that
uniquely identifies an instance of an entity
o Attributes that are identifiers are prefixed by an asterisk
o Entities are things in the environment about which we wish to
store info. Attributes describe an entity. An entity must have a
unique identifier.
Data model to relational database translation rules:
o Each entity becomes a table
o Entity name becomes the table name
o Each attribute becomes a column
o Identifier becomes the primary key
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