2.1.2. Modeling Data with Entity Relationship Diagrams

What is the relationship element?

A relationship describes how entities interact Relationships are represented by diamond shapes and are labeled using verbs

What is an entity relationship diagram (ERD)?

A visual representation of different data using conventions that describe how these data are related to each other

What is weak entity?

A weak entity is an entity that depends on the existence of another entity In more technical terms it can be defined as an entity that cannot be identified by its own attributes Represented with a rectangle with one rectangle within the larger rectangle

What is the attribute element?

An attribute is a property, trait, or characteristic of an entity, relationship, or another attribute Attributes can also have their own specific attributes - composite attributes Attributes are represented by oval shapes

What is the entity element?

An entity can be a person, place, event, or object that is relevant to a given system Entities are represented in ER diagrams by a rectangle and named using singular nouns Represented with a rectangle

What are the two types of standards for ERDs?

Chen's Database Notation and Crow's Foot Database Notation

What is the difference between Chen's Database Notation and Crow's Foot Database Notation?

Chen's Database Notation is formatted with shapes and arrows Crow's Foot Database Notation is formatted in a table

In what two areas are ERDs used?

ER Models in Database Design - They are widely used to design relational databases - The entities in the ER schema become tables, attributes and converted the database schema ER diagrams in software engineering -Entity relationship diagrams are used in software engineering during the planning stages of the software project -They help to identify different system elements and their relationships with each other

What are some benefits to ERDs?

ER diagrams are easy to understand and do not require a person to undergo extensive training to be able to work with it efficiently and accurately ER diagrams are readily translatable into relational tables which can be used to quickly build databases ER diagrams may be applied in other contexts such as describing the different relationships and operations within an organization

What are the three basic elements of ERDs?

Entity, attribute, and relationship

What are some best practices for ERDs?

Provide a precise and appropriate name for each entity, attribute, and relationship in the diagram. Remove vague, redundant or unnecessary relationships between entities. Never connect a relationship to another relationship. Make effective use of colors.

What is weak relationship?

Represented with a diamond but has one diamond within the larger diamond

What are three other elements to ERDs?

Weak entity, multivalued attribute, and weak relationship

How do you draw ERDs?

Identify all the entities in the system. - An entity should appear only once in a particular diagram. - Create rectangles for all entities and name them properly. Identify relationships between entities. - Connect them using a line and add a diamond in the middle describing the relationship. Add attributes for entities. - Give meaningful attribute names so they can be understood easily.

What is multivalued attribute?

If an attribute can have more than one value it is called a multi-valued attribute Represented with a oval but has one oval within the larger oval

What is a recursive relationship?

If the same entity participates more than once in a relationship it is known as a recursive relationship Example: an employee can be a supervisor and be supervised