Lecture 4: Data modelling and Databases

Question 1

Describe and explain the role of database management systems in ensuring information quality in transaction processing

Answer 1

Database management system is a software application with which you can create, store, organise and retrieve data from one or many databases. DMBS can help ensure validity, accuracy, completeness and timeliness of information by:
• Providing security controls
• Maintaining audit trials
• Providing an integrated enterprise-wide data repository (‘storeroom’)

DMBS helps enforce integrity rules:

• Relation integrity in that no duplicates or blanks are allowed for primary key attribute value
• Referential integrity, the value entered in FK attribute must exists as a value in corresponding relation’s PK

Question 2

What are relational data models and what are the advantages?

Answer 2

• Relational data model is a data model that stores information in the form of related two-dimensional tables.
• Allows users to identify relationships at the time database is created or much later whenever new info requirements from the model are desired.
• Advantages include:
  • Flexibility (can handle changes in info requirements quickly)
  • Simplicity (easily communicated)
  • Reduced information asymmetry (eliminates need for info to be stored in multiple places, helps keep info undated and avoid inconsistency)

Question 3

What are the important elements in data models?

Answer 3

1. Class, which is any separately identifiable collection of things about which the organisation wants to collect and store info.
2. Association, depicts the relationship between the two classes.
3. Multiplicities, describe the min and max number of instance in which one class can be associated with that of another class
4. Attributes, data elements that describe the instances in a class
   • Primary Key—an attribute/combination of attributes that uniquely identify each instances in a class (E.g. PK of inventory would be inventory number)
   • Foreign Key—allows the tables to be linked together. Linked to the primary key of another table to support defined association (E.g. Sales Table—links customer and inventory—FK: customer number and item number)
   FK are the PKs of the tables that the table is linking together

Question 4

What are ER Diagrams?

Answer 4

• Entity-Relationship (ER) diagram is a data modelling technique that graphically illustrates an information system’s entities and the relationships between those entities.

Three elements:

• Entities (persons, place, objects, events or concepts)
• Relationships (association b/w entities—VERBS)
• Attributes (characteristics description of entity)

Question 5

What are REA Diagrams?

Answer 5

• Resources, Events, Agents (REA) diagram

Three elements:

• Resources (things that have economic value to firm, e.g. cash and products)
• Events (various business activities conducted in firm’s daily operations, e.g. sales and purchases)
• Agents (people who participate in business events, e.g. customers and salespeople)
• Unlike other approaches, REA reveals why business processes occur and provides for full traceability of business transactions