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IDEF1X, Crowsfoot and Chen Modeling ER Diagrams


IDEF1X

The image illustrates three different Entity-Relationship Diagram (ERD) notation:
  1. IDEF1X
  2. Crow’s Foot
  3. Chen Notation

modeling the same relationship between `OFFICE` and `EMPLOYEE`. Each style conveys the one-to-many relationship with distinct visual syntax:

  1. ✅ IDEF1X Model

    • Symbols Used:
      • Solid black circle on the EMPLOYEE side: indicates a dependent entity.
      • Diamond connector: indicates a relationship.
      • Solid line: represents an identifying relationship (child inherits part of the parent’s PK).
    • Interpretation:
      • EMPLOYEE is a dependent entity.
      • Each employee must be assigned to exactly one office.
      • An office can have many employees.
      • This is a mandatory one-to-many (1:N) identifying relationship.

  2. ✅ Crow’s Foot Model

    • Symbols Used:
      • Two vertical bars (||) next to OFFICE: indicates mandatory one.
      • Crow’s foot with a circle near EMPLOYEE: indicates zero or many.
    • Interpretation:
      • Each employee may or may not be assigned to an office.
      • Each office must have one or more employees.
      • This represents a mandatory one-to-many relationship from OFFICE to EMPLOYEE, but with optional participation from EMPLOYEE.

  3. ✅ Chen Model

    • Symbols Used:
      • Diamond labeled "assign": denotes the relationship.
      • "1" near OFFICE and "N" near EMPLOYEE: represents cardinality.

🔄 Comparison Table
Notation Relationship Type Direction Optionality / Notes
IDEF1X Identifying 1:N OFFICE → EMPLOYEE EMPLOYEE is dependent on OFFICE
Crow’s Foot Mandatory 1 to (0..*) OFFICE → EMPLOYEE EMPLOYEE can be optionally assigned
Chen 1:N OFFICE → EMPLOYEE Uses "assign" to describe relationship

Interpretation:
  • Each employee is assigned to one office.
  • Each office may have many employees.
  • This is a standard 1:N (one-to-many) relationship.

📌 Summary All three notations express the same logical model: an OFFICE can have many EMPLOYEEs, but the notations differ in how they depict cardinality, dependency, and optional participation. The choice of notation depends on the modeling standard used in the organization or project.

I. IDEF1X Notation

Question:
  1. "What is IDEF1X ?" or
  2. "What does this symbol mean?"
and consequently we go off on a side trip.
Answer: This page introduces IDEF1X and identifies the notation, so that standard-compliant data models can be read and fully understood. There are many closely related subjects, which require formal education and the links are provided below in the list.
  1. the Relational Model
  2. 2nd and 3rd Normal Forms in general, and the specific Relational Normalization identified in the Relational Model.
  3. The IDEF1X Methodology or Relational Database Design


Item: Key, Entity, Relation
Item Definition Display
Key
Primary Key Unique Above line
Alternate Key Other Unique key AK
Inversion Entry Non-Unique index IE
Entity
Independent Exists without a parent Square
Dependent Dependent on a parent Round
Relation
Identifying Parent PK forms child PK Solid line
Non-Identifying Parent PK is not child PK Broken line
Parent PK is always a migrated FK in child Bold

  • Item: Key, Entity, Relation
  • Key Definitions:
    • Primary Key: Unique
    • Alternate Key: Other Unique key
    • Inversion Entry: Non-Unique index
  • Entity Definitions:
    • Independent: Exists without a parent
    • Dependent: Dependent on a parent

  • Relation Definitions:
    • Identifying: Parent PK forms child PK
    • Non-Identifying: Parent PK is always a migrated FK in child
  • Display Notations:
    • Primary Key: Above line
    • Alternate Key: AK
    • Inversion Entry: IE
    • Independent Entity: Square
    • Dependent Entity: Round
    • Identifying Relation: Solid line
    • Non-Identifying Relation: Broken line
    • Parent PK in Non-Identifying Relation: Bold

Description of Relevant Features:
  • Design and Layout: The table is organized into three columns: Item, Definition, and Display. This layout helps in clearly distinguishing between the terminology, its definition, and its visual representation in IDEF1X diagrams.
  • Notation Symbols: The use of different symbols and lines to represent various database concepts (like primary keys, alternate keys, and types of relations) aids in visually differentiating the components of a database schema.
  • Use of Text Styles: Bold and italics are used to emphasize key aspects of the notation, such as the primary key always being a migrated foreign key in non-identifying relationships.
  • Clarity and Purpose: The image provides a quick reference for understanding how different elements are represented in an IDEF1X model, which is beneficial for database designers and those studying database modeling.

These features make the IDEF1X method and notation effective for visually representing complex database schemas in a structured and standardized manner.

Database Systems

IEEE Relation Notation:

IEEE Relation Notation
  • IEEE Relation Notation:
    • Identifying: 1:1-n
    • Identifying: 1:0-n
    • Non-Identifying: 1:1-n
    • Non-Identifying: 1:0-n
    • Subtype: 1:0-1
    • Logical Only: 1-n:1-n
  • Symbols for Relations: Subtype Exclusive: Subtype Non-exclusive
  • Entity Type:
    • Reference Authority
    • Reference
    • Identifying Entity
    • Transaction
    • Transaction Detail
    • Exposed
    • History, Audit

Description of Relevant Features:

  • Notation Style: The diagram uses various arrows and lines to represent different types of relationships in a database, such as identifying and non-identifying relationships.
  • Entity Type List: A list of different types of entities such as Reference Authority, Transaction Detail, etc., likely represents different roles or purposes that entities might have within a database schema.
  • Subtype Indicators: Circles marked "Subtype Exclusive" and "Subtype Non-exclusive" are likely used to indicate whether an entity can simultaneously be more than one subtype or exclusively one subtype.
  • Relationship Multiplicity: The notation 1:1-n, 1:0-n, 1:0-1, 1-n:1-n provides the cardinality and optionality of the relationships, indicating how many instances of an entity type can be associated with instances of another type.
  • Logical Representation: The "Logical Only" relationship suggests a conceptual link that might not necessarily be implemented directly in the database but is important for understanding the schema.
  • Clarity and Educational Value: The diagram provides clear, visual representations that can help users quickly understand complex relationships and entity types in database design, making it a useful educational and reference tool.

This style of representation is essential for database designers, especially in complex systems, where understanding the relationships between different entities accurately is crucial for data integrity and performance.

Database Systems
Context and Purpose
  1. IDEF1X stands for Integrated Definition, and belongs to a set of six such definitions, each of which is tightly constructed and integrated with the others. 1 is for Information Modelling, 1X is for Relational Data Modelling.
  2. It is a stricter implementation of the Relational Model by Dr E F Codd. It is based on the theory and techniques invented by Codd (the RM) and Dr P P S Chen (the Entity Relation Model). The initial technique (methodology) was developed by R R Brown, T L Ramey and D S Coleman. It was progressed and developed to this diagrammatic form by Robert Brown in the early 1980s.
  3. It is a methodology, specifically for modelling Relational databases.
  4. It was accepted and declared as a standard by National Institute of Standards and Technology (FIPS 184) in 1993. (IDEF0 may be used for Function Modelling.)
  5. It allows the data to be modelled:
    1. in the context of the whole organisation
    2. independent of the applications that use it
    3. completely (exposing all complexities and subtleties).
    4. using a standard notation (set of symbols) and nomenclature, so that all teams and users are served. This eliminates ambiguity, and ensures that the complete set of information (identified by the standard) is communicated in the single diagram.
  6. Competent use of the Methodology produces databases that are easy to change and extend, as well as easy to use, by users and future applications. The result is a more genuinely Relational database, which allows expansion, rather than replacement due to the limitations otherwise
  7. IDEF1X is widely accepted in organisations that require compliance to Standards (Government departments, US DoD, aircraft manufacturers, large banks). It is viewed as a mark of quality, a genuine Relational database.

II. Crows Foot Notation and Example

Detailed Diagram outlining Crows Foot Notation
Crows Foot Notation

Detailed Diagram outlining Crows Foot Notation
The Crow’s Foot Notation diagram depicts the relationship between two entities: ACCOUNT and BANK.
Break down the relationships shown in the diagram:
🧾 Entities and Attributes
  1. ACCOUNT
    • Has a primary key attribute: * number
    • This implies that the number is a unique identifier for each account.
  2. BANK
    • Has a composite key: #* number
      • The # symbol typically denotes that it is a foreign key, while * means it’s also a primary key.
      • So number in BANK is part of its primary key and may be a foreign key in some cases.

🔁 Relationships
There are two variations of the relationship depicted:
  1. First Relationship (Middle of Image):
    • Labeled: "managed by" from ACCOUNT to BANK
    • The relationship text on the reverse path is: "the manager of"
    • The symbol between the entities:
      • Crow’s foot at ACCOUNT side → indicates many accounts
      • Circle and dash at BANK side → means optional one bank
    • Interpretation:
      • Each ACCOUNT is optionally managed by one BANK.
      • A BANK can manage many ACCOUNTS.
      • Some accounts might not be managed by any bank, indicating the optionality.
  2. Second Relationship (Bottom of Image):
    • Also labeled: "managed by" from ACCOUNT to BANK
    • But the symbol changes at the BANK side:
      • Straight line and dash (instead of circle) → indicates mandatory one bank
    • Interpretation:
      • Each ACCOUNT must be managed by one BANK.
      • A BANK can manage many ACCOUNTS.
      • This is a mandatory 1:N relationship (1 Bank ↔ N Accounts), with no optionality on the ACCOUNT side.
⚖️ Comparison Between Two Diagrams
Aspect Top Version (Middle) Bottom Version
Account to Bank Optional many-to-one Mandatory many-to-one
Bank to Account One bank → many accounts One bank → many accounts
Optionality on Bank side Yes (optional bank) No (must have a bank)

📌 Summary This Crow's Foot diagram presents a 1-to-many relationship between BANK and ACCOUNT:
  • A BANK can manage multiple ACCOUNTS
  • An ACCOUNT can be managed by:
    • Optionally one bank (middle diagram)
    • Or must be managed by one bank (bottom diagram)
Detailed Diagram outlining Crows Foot Notation

Chen Notation

Figure 7-3 shows the different types of relationships using two ER notations:
  1. the original Chen notation and the
  2. Crow's Foot notation.

The left side of the ER diagram shows the Chen notation, based on Peter Chen's landmark paper. In this notation, the connectivities are written next to each entity box. Relationships are represented by a diamond connected to the related entities through a relationship line. The relationship name is written inside the diamond.
The right side of Figure 7-3 illustrates the Crow's Foot notation. The name "Crow's Foot" is derived from the three-pronged symbol used to represent the “many” side of the relationship. As you examine the basic Crow's Foot ERD in Figure 7-3, note that the connectivities are represented by symbols.
For example, the "1" is represented by a short line segment, and the "M" is represented by the three-pronged "crow's foot." In this example, the relationship name is written above the relationship line.
In Figure 7-3, entities and relationships are shown in a horizontal format, but they may also be oriented vertically. The entity location and the order in which the entities are presented are immaterial; just remember to read a 1:M relationship from the "1" side to the "M" side.
The Crow's Foot notation is used as the design standard in this book. However, the Chen notation is used to illustrate some of the ER modeling concepts whenever necessary. Most data modeling tools let you select the Crow’s Foot notation.

Each of the three diagrams on represents the same relationship type as its corresponding Chen diagram. The explanatory text below each individual diagram is identical and aligned horizontally across both notation styles:
  • Top (1:1) "One to One" -> EMPLOYEE–STORE
  • Middle (1:M) "One to Many" -> PAINTER–PAINTING
  • Bottom (M:N) "Many to Many" -> EMPLOYEE–SKILL

A One-to-One (1:1) Relationship:
1) (One-to-One):> A One-to-One (1:1) Relationship: an EMPLOYEE manages one STORE; each STORE is managed by one EMPLOYEE.

A One-to-Many (1:M) Relationship:
2) (One-to-Many):> A One-to-Many (1:M) Relationship: a PAINTER can paint many PAINTINGS; each PAINTING is painted by one PAINTER.

A Many-to-Many (M:N) Relationship:
2) (Many-to-Many):> A Many-to-Many (M:N) Relationship: an EMPLOYEE can learn many SKILLS; each SKILL can be learned by many EMPLOYEEs.

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