L9 - Entity Reation Modeling

Question 1

What is a database?

Answer 1

• Shared collection of logically related data (with description)
• Designed to meet the needs of an organisation
• Which is stored and accessed electronically from a computer system

Question 2

What is the database approach?

Answer 2

Question 3

What is a DBMS?

Answer 3

What is a DBMS (Database Management System)

Software that enables users to:

• Define a database
• Create a database
• Maintain a database
• To control access to the database

Question 4

How can users interact with a DBMS?

Answer 4

• General inquiry facility to the data via Query Language
  
  • SQL
• Standard User Interface
• Users can generate their own queries

Question 5

What services does a DBMS provide

Answer 5

• Preserve integrity of the data
  
  • Defined by constrains
• Preserve data independence
  
  • Protecting users from system changes
• Extra Utilities
  
  • Import/Export
  • Performance profiling

Question 6

What is a an application of a Database Context?

Answer 6

A computer program that interacts with the database by issuing an appropriate request (SQL Statement) to the DBMS

• Can be a CLI
• Typically a GUI
  
  • Wrapped around preset queries

Question 7

What are the advantages of the Database Approach?

Answer 7

• Control of data redundancy
• Data consistency
• Easier to share data
• Improved data independent + integrity

Question 8

What are the disadvantages of the Database Approach?

Answer 8

• Complex
• Running cost of DBMS
• Conversion cost
• Performance
• Higher impact of failure

Question 9

What is the realtional model?

Answer 9

• Replaces tree/network models
• Basis for set-oriented data manipulation language (SQL)
• High degree of data independence
  
  • Users cant make physical changes
• Improved control of self-describing, consistency and redundancy

Question 10

What are data models?

Answer 10

• Represents the operational requirements of an organisation
• Made up of
  
  • Structural part
  • Manipulative part
  • Integrity Rules

Question 11

What is the Relational Data Structure?

Answer 11

Relational data model components:

• Relation
• Attribute
• Tuple
• Domain
• Relational Database

Question 12

What the properties of realtional tables?

Answer 12

• Distinct table names
• Distinct column/attribute names
• Distinct record/row tuple is distinct
• Atomic cells
• Column values are from the same domain

Question 13

What are the different types of realtional keys?

Answer 13

Superkey

• Any set of columns that uniquely identifies all records
• Composite key has > 1 column

Candidate key

• Minimal set of columns

Primary Key

• Chosen candidate

Alternate Key

• Remaining candidate

Foreign Keys

• Represents a relationship between two tables
• Provides controlled redundancy

Question 14

What is relational integrity?

Answer 14

• Every column is subject to domain contrints
• Entity integrity
• Referential integrity
• Ensures consistency
  
  • Allowing minimal redundancy
• Allows for set manipulation operations to be reliably performed on data across tables

Question 15

What are integrity rules?