FEN 2015-08-31 1

Introduction to the database field:

Conceptual modelling:The Entity-Relation (ER) Model

Seminar:Introduction to relational databases

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…or…

Where does all the tables come from???

FEN 2015-08-31

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Conceptual Data Models

A conceptual data model describes the data objects (entities) and their relations in the problem domain.A conceptual model of the data is the basis on which the IT systems of an organisation are build.It should be:

Independent of implementationStable over time

Over time conceptual data structure doesn't change nearly as much as functionality

Conceptual models are to be transformed to a database model – for instance the relational model.

FEN 2015-08-31

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Example: MiniBank

This is conceptual (ER-model):

FEN 2015-08-31

What would a conceptual model look like?• Entities?• Customer• Account

• Relations:• Customer-Owns-Account

Customer Account

custNo name accNo balance

inRate

Owns1 n

This is implementation:

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Entity-Relation (ER) Model: ConceptsEntities

Attributes⋅ Atomic⋅ Composite⋅ Multi valued

Attribute valuesEntity typesKeysDomains

FEN 2015-08-31

RelationsCardinality ratioParticipation (total / partial)Relations may have attributes

Weak Entity TypesIdentifying ownerIdentifying relationPartial keyA weak entity always has total participation in the identifying relation.

Customer Account

custNo name accNo balance

inRate

Owns1 n

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Example: The Company Database (Elmasri)

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Entities?

FEN 2015-08-31

Department: name(kk), number(kk), locationProject: name(kk), number(kk), locationEmployee: ssn(kk), bdate, name (poss. composite), sex, address (poss. composite), salaryDependent (weak?): name (partial key), sex, bdate

Example: The Company Database (Elmasri)

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Relations?

FEN 2015-08-31

ManagesWorks_ForWorks_OnDependents_OfSupervisionControls

Example: The Company Database (Elmasri)

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ER Diagram for the Company Database

FEN 2015-08-31

Example: The Company Database (Elmasri)

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Example/Exercise (Elmasri)

FEN 2015-08-31

Questions:Can a customer exists without an account?Can an account have more owners?How many branches can account belong to?Can a customer have accounts in more than one branch?…???