What Data Models Are There?

Relational Model

• All data is represented as a set of "tables"

• The most "popular" data model used for database systems

• I.E School Information

  

Terminology of Relation Modal

we can use the example above for this

• Each relation has a set of attributes (= columns)

• Each relations contains a set of tuples ( = rows)

• Each attribute has a domain ( = type )

  • attributes can only be atomic types

• Schema: the structure of relations in database

  • Relation name, attribute name, domain(optional)
  • Ex: Student(sid, name, addr, age, GPA)

• Instance(= Data)

  • Actual content of the relation
    • Schema ~= variable type, Instance ~= value

• Keys: A set of attributes that uniquely identifies a tuple in relation

  • Student(sid, name, addr, age, GPA)
    • sid can be a key here, so does (name, addr)
    • Among all the keys, we only pick one as the primary key
  • Course(dept, cnum, sec, unit, instructor, title)
  • Underline key attributes in schema

Name Scope

• Name of a relation is unique in a table
• Name of an attribute is unique in a table
  • Same attribute name in different tables is OK