DBMS - Symbols in ER-Diagram

Summary

This session provides an overview of ER (Entity-Relationship) diagrams and the various symbols used in them. It explains key concepts such as entity sets (denoted by rectangles), weak entity sets, relationship sets (denoted by diamonds), and their attributes. The video covers many-to-many, one-to-one, and many-to-one relationships, along with role indicators, multivalued and derived attributes, and cardinality limits. Generalization and specialization in ER diagrams are briefly introduced, with further videos promised for deeper discussions on specific topics. Overall, it offers a foundational understanding of ER diagram components and notations.

Takeaways

• 📦 The entity set is denoted by a rectangle, and the entity name is written inside it.
• 🚫 A weak entity set does not have a primary key, only a partial key.
• 💎 A relationship set is represented by a diamond, with the relationship name written inside.
• 🔗 Identifying relationships are represented by double diamonds, with their names inside.
• 🔑 Attributes are enclosed in ellipses, and primary keys are underlined.
• 🔄 In a many-to-many relationship, there are no arrows across the edges.
• ➡️ In a one-to-one relationship, there are arrows in both directions, while in a many-to-one relationship, the arrow points from many to one.
• 📝 Role indicators are shown by writing the role name across the line connecting the entity and the relationship.
• 🔁 Multi-valued attributes are denoted by a double ellipse, and derived attributes are enclosed in dashed ellipses.
• 🌐 Total participation of an entity set in a relationship is shown by double lines, while cardinality limits are denoted with '1..N'.

Q & A

What symbol is used to represent an entity set in an ER diagram?

An entity set is represented by a rectangle in an ER diagram, with the entity name written inside the rectangle.

How is a weak entity set represented in an ER diagram?

A weak entity set does not have a primary key and is represented by a rectangle. It includes a partial key, which will be discussed in a separate video.

What shape is used to denote a relationship set in an ER diagram?

A relationship set is denoted by a diamond, with the relationship name written inside the diamond.

How is an identifying relationship shown in an ER diagram?

An identifying relationship is shown using a double diamond, with the relationship name written inside the double diamond.

How are attributes represented in an ER diagram, and how is a primary key attribute distinguished?

Attributes are represented by ellipses in an ER diagram. If the attribute is a primary key, the name of the attribute is underlined.

How is a many-to-many relationship indicated in an ER diagram?

In a many-to-many relationship, there are no arrows across the edges connecting entities to the relationship set.

What distinguishes a one-to-one relationship in an ER diagram?

A one-to-one relationship is shown with arrows pointing in both directions between the entities involved.

How is a multivalued attribute shown in an ER diagram?

A multivalued attribute is represented by a double ellipse in an ER diagram.

What symbol is used to represent total participation of an entity set in a relationship?

Total participation is represented by double lines between the entity set and the relationship in the ER diagram.

How is generalization and specialization represented in an ER diagram?

Generalization and specialization are represented by a triangle labeled with 'is a', indicating that one entity is a specialized version of another.