LU04.S06 - ERM vs. ERD

• Work type: Peer
• Means of aid: only teaching materials, no use of ai.
• Timeframe: 5 Minutes
• Expected result: A Word/PDF file with an a comparison of the terms ERM vs. ERD.

Compare both terms, ERM and ERD, and describe the purpose of each, and find at least 2 similarities and 2 differences.

ERM

• Description: First step to find the entities and the correlations between them.
• Purpose: Blueprint of the business cases

ERD

• Description:Identification of details, such as data-types, relation-table and the cardinality
• Purpose: construction plan, ready to build up the data-base physically

Similarties

• Both notation methods are used to describe the data-base structure of the business cases
• Entity = rectangle
• Cardinalities: 1:1, 1:n, n:m
• Entities have attributes

Differences:

• Relations:
  • ERM: rhomb
  • ERD: relalation-table
  • ERD: Described in the Crow's foot notation
• Attributes:
  • ERM: bubbles above, which are connected with the entity
  • ERD: As details in the Entity, including data-type
  • ERD: Memory amount is describes within the data-type defintion

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