INTRODUCTION TO DATABASE DESIGN

Definitions Database Models: Conceptual, Logical, Physical Conceptual: “big picture” overview of data and relationships Logical: what data needs to be represented Physical: how data is to be stored using a particular type of DBMS

CONCEPTUAL DATA MODEL (High Level, Big Picture) Identify and represent important data and relationships Focus on data (‘what’), not process (‘how’) Conduct informal brainstorming sessions with client representatives Iterate - revise constantly

CONCEPTUAL DATA MODEL COMPONENTS Identify ENTITIES - important things (person, place, thing or event) in system that information is to be maintained ; eg STUDENT, TIMETABLE, SUBJECT, PROGRAM, CLASS, ROOM, … Identify ATTRIBUTES - characteristic or piece of information that helps to describe an entity; eg STUDENT: id, name, address, program, learn account; SUBJECT: subject code, name, description, …

CONCEPTUAL DATA MODEL COMPONENTS(ctd) Identify CANDIDATE KEY(S) for each entity: group of 1 or more attributes which uniquely identify a single occurrence or instance of an entity ; eg STUDENT: ID, SIN Choose a PRIMARY KEY for each entity from candidate keys identified- candidate key that most appropriately uniquely and minimally identifies a particular instance or ocurrence of an entity; eg STUDENT: ID, SUBJECT: SUBJECT CODE

CONCEPTUAL DATA MODEL COMPONENTS(ctd) Identify RELATIONSHIPS - logical links between entities; eg a STUDENT is registered in a program and a program may have one or more students registered Identify CARDINALITY of each relationship - 1:1, 1:m, m:n and mandatory or optional; eg a STUDENT must be registered in only one program and a program may have zero, one or more than one student registered

CONCEPTUAL DATA MODEL COMPONENTS(ctd) Prepare ENTITY-RELATIONSHIP DIAGRAM as Conceptual Data Model Present Conceptual Data Model to clients and review and revise as additional information is received

ENTITY RELATIONSHIP DIAGRAM (ERD) Single ERD represents conceptual model of all data for system Symbols: Rectangle - Entity; Line – Relationship, Diamond – Relationship Label; crowsfeet - Cardinality ERD is to be read in any direction