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Lesson 3 Types of entity-relationship diagrams
ObjectiveDescribe the types of entity-relationship diagrams.

Types of Entity-relationship Diagrams

The three best-known types of ER diagrams are:
  1. The Crowsfoot model: One of several types of entity-relationship (ER) diagrams, the Crowsfoot model neatly packages entities with their attributes by placing them in boxes. Also referred to as the Information Engineering model. Crowsfoot model also called the Information Engineering model.
  2. The Chen model: One of several types of entity-relationship ER-diagrams. The Chen model is named after the inventor of ER diagramming Chen model.
  3. The IDEF1X model (the least well-known of the three)

To get a sense of how different (but also, of how similar) these three models are, consider the following business rule, captured by each type of diagram: "An office is assigned to employees." (Do not be concerned at this point with interpreting the diagrams, you will learn how to do that shortly.)

I. Crow's foot Model

The relationship between eBusiness and eCommerce
Crow's foot Model: One of several types of entity-relationship (ER) diagrams, the Crow's foot model neatly packages entities with their attributes by placing them in boxes. Also referred to as the Information Engineering model.

II. Chen Model

Chen Model
The Chen model is named after the inventor of ER diagramming. The Entity-Relationship model was introduced by Chen (1976), and related work appears in Schmidt and Swenson (1975).

III. IDEF1X Model

ERD types
The IDEF1X Methodology or Relational database design.
  1. IDEF1X stands for Integrated Definition,
  2. 1 is for Information Modelling,
  3. 1X is for Relational Data Modelling.

Weigh the Pros and Cons of the Three Different Models

I will provide a brief overview of each model's advantages and disadvantages.

I. Crowsfoot Model:

Advantages:
  1. Simplicity: The Crowsfoot model is arguably the easiest ER model to understand and interpret due to its minimalistic notation. The relationship types and cardinality are clearly marked on the diagram, making it suitable for simple and quick modeling exercises.
  2. Visual clarity: The Crowsfoot notation uses distinctive symbols, which can be easily distinguished, adding to its ease of comprehension.
  3. Flexibility: The model can easily accommodate various relationship types, including one-to-one, one-to-many, and many-to-many.

Disadvantages:
  1. Limited expressiveness: Despite its simplicity, the Crowsfoot model falls short when it comes to modeling more complex relationships, and doesn't directly support concepts like inheritance or disjoint relationships.
  2. No standardization: There is no standardization or widely accepted version of the Crowsfoot notation, leading to potential confusion and inconsistency across different implementations.

Chen Model:

Advantages:
  1. Expressiveness: The Chen model is well-regarded for its ability to accurately represent complex relationships. It directly supports concepts like inheritance, disjoint relationships, and explicit relationship types.
  2. Standardization: The Chen model is a standardized form of ER diagrams, which helps ensure consistency across different databases and systems.
  3. Semantic clarity: The Chen model uses clear, verbose symbols to describe entity relationships, which can help in understanding the business rules being represented.
Disadvantages:
  1. Complexity: The Chen model's thoroughness comes at a cost – it can be quite complex to read and understand, particularly for those without prior database or systems design experience.
  2. Verbose Notation: The model's verbosity can lead to crowded and complex diagrams, especially for larger systems, potentially leading to difficulty in comprehending the model.

IDEF1X Model:

Advantages:
  1. Extensive capabilities: The IDEF1X model is designed to support a broad array of data modeling needs, including complex relationships, constraints, keys, and more.
  2. Standardization: IDEF1X is a standard developed by the US National Institute of Standards and Technology (NIST), which aids in consistency.
  3. Integrity rules: This model provides explicit notations for constraints and integrity rules, making it beneficial for systems where data integrity is paramount.
Disadvantages:
  1. Learning Curve: The IDEF1X model's extensive capabilities come with a steep learning curve. It has a complex notation system that can be difficult to understand for novices.
  2. Complexity: The diagram can become overly complex and hard to read when modeling larger systems due to its rich set of symbols and notations.
In summary, the choice of ER model can greatly depend on the specific requirements of the system being modeled, the familiarity and expertise of the modeling team with different notations, and the trade-offs between simplicity, expressiveness, and complexity.
There is no "standard" ER diagram. Many others, in addition to the three described above are in use. Fortunately, once you have learned to interpret one of them, it is fairly easy to learn how to read any of the others.
In this module, you will work exclusively with the Crowsfoot model.
The next lesson illustrates the conventions used to diagram entities and attributes with the Crowsfoot model. Before moving on to the next lesson, click the link below to see if you can identify the three best-known types of ER diagrams.
idef1x Crowsfoot | Chen-model

Database Modeling