Entity-Relationship Model Advantages and Disadvantages

Data Models

• ER Model (Entity-Relationship Model) is a high-level data model that defines data elements and relationships for a specified system.
• It develops a conceptual design for the database and portrays the database structure as an ER diagram.
• ER model can be easily converted to relational model and other models like network model, hierarchical model, etc.

Disadvantages of ER Model

• No industry standard for notation, leading to differences in notation between developers.
• Hidden information, as it is a high-level view, and some details might be lost.

Relational Model

• Most widely used model, where data is maintained in a two-dimensional table.
• Basic structure is tables, also called relations.
• Features:
  • Tuples: each row in the table contains all the information about an instance of the object.
  • Attributes or fields: properties that define the table, with values from the same domain.

Advantages of Relational Model

• Simple, compared to network and hierarchical models.
• Scalable, as rows and columns can be easily added.
• Structural independence, allowing changes to the database structure without affecting data access.

Disadvantages of Relational Model

• Hardware overheads, requiring more powerful computers and data storage devices.
• Bad design, which can lead to a poor database that slows down if the database grows.

Object-Oriented Data Model

• Represents real-world problems closely, with both data and relationships in a single structure, an object.
• Gives flexibility in storing data and attributes.
• Example: an attribute can have an atomic value or a collection of values.

Associative Data Model

• Divides data into two parts: entities and associations.
• Items contain the name and identifier, while links contain the identifier, source, verb, and subject.
• Example: storing information about the world cup being hosted by London.

Context Data Model

• A collection of models, including network, relational models, etc.
• Allows for various tasks not possible with a single model.

Database Schema

• A database schema is the skeleton structure that represents the logical view of the entire database.
• Includes people, techniques, and data within the database environment.

Data Modeling

• A technique to document a software system using diagrams and symbols.
• The highest level of abstraction is the Entity Relationship Diagram (ERD).

Entity Relationship Diagram

• A graphical representation of data requirements for a database.
• Components:
  • Entities: number of tables needed for the database.
  • Attributes: information to describe each table.
  • Relationships: how tables are linked together.

ER Diagram Components

• Entities:
  • Represented as rectangles.
  • Examples: manager, product, employee, department.
• Weak Entities:
  • Depend on another entity.
  • Represented as double rectangles.
• Strong Entities:
  • Represented as single rectangles.
  • Examples: student, course.