ISOM221+Lecture+9+-+Data+Modeling+II

ISOM221+Lecture+9+-+Data+Modeling+II - ISOM221 Information...

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ISOM221 Information Systems Analysis and Design Lecture 9: Data Modeling II 1 Last Class Understand the key definitions of ERD Understand ERD elements Understand the concepts of cardinality and modality 2
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Agenda Learn how to construct an ERD Learn the concept of normalization Learn how to balance ERDs with DFDs 3 ERD Basics Drawing the ERD is an iterative process of trial and revision ERDs can become quite complex 4
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Steps in Building ERDs Identify the entities Add attributes and assign identifiers Identify relationships 5 Step 1: Identify the Entities Identify major categories of information If available, check the process models for data stores, external entities, and data flows Verify that there is more than one instance of Verify that there is of the entity that occurs in the system 6
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Step 2: Add Attributes and Assign Identifiers Identify attributes of the entity that are relevant to the system under development Check the process model for details on data flows and data stores Check the data requirements of the requirements definition Interview knowledgeable users Perform document analysis on existing forms and reports Select the entity’s identifier 7 Step3: Identify Relationships Start with an entity and identify all entities with which it shares relationships Describe the relationship with the appropriate verb phrase Determine the cardinality and modality by discussing the business rules with knowledgeable users 8
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ERD Building Tips Data stores of the DFD should correspond to entities Only include entities with more than one instance of information 9 Design Modeling Guidelines Summary 10
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Example: Tune Source Digital Music Download System 11 Step 1: Identify the Entities 12
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Step 2: Add Attributes and Assign Identifiers 13 Step3: Identify Relationships (Please determine cardinality and modality) 14
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ISOM221+Lecture+9+-+Data+Modeling+II - ISOM221 Information...

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