Lecture 4

Question 1

Data Abstraction Layers

Answer 1

3 different ways of modeling data in a domain

• Conceptual,
• logical and
• physical model

SAME: entities and relationships

DIFFERENCE: purposes, audiences

Question 2

Entity Relation Diagram (ERD)

Answer 2

Entity relationship diagram (ERD) represents a detailed picture of the entities needed for a business. Can be conceptual, logical and physical.

Question 3

external model

Answer 3

the end-users’ view of the data (needs)

Question 4

tools for external modeling

Answer 4

• requirements gathering: interviews, focus groups, existing documentation, etc.
  
  • concept template
  • defintion of keywords
  • grain matrix
  • deminsional and relational models

Question 5

tools for conceptual modeling

Answer 5

• Concept template and definition of keywords
• List of questions and grain matrix
• Dimensional and relational models (e.g. ER-Conceptual model, network model, Axis technique, etc.)

Question 6

Conceptual models

Answer 6

information gathered from business requirements

efficiency and effectiveness is not considered yet

Question 7

Logical ER model

Answer 7

• also models information gathered from business requirements
• column types are set
• A logical ER model is normally a conceptual model transformed into a full ER model and normalised

Question 8

Physical ER model

Answer 8

It represents how data should be structured and related in a specific DBMS

• so it is important to consider the convention and restriction of the DBMS

Besides, database designers may also add primary keys, foreign keys and constraints to the design which were not evident in the logical design