Create an Entity Relationship Diagram (ERD) for your ISP. So, why do we create ERDs? When documenting a
system or process, looking at the system in multiple ways increases the understanding of that system. ERD
diagrams are commonly used in conjunction with a data flow diagrams to display the contents of a data base.
They help us to visualize how data is connected in a general way, and are particularly useful for constructing a
relational database. Keep in mind these are separate and distinct diagrams: the ERD addresses entities where
the DFD does not; the DFD represents numbered processes and there are no entities on it except for the
context diagram.
Here are some best practice tips for constructing an ERD:
Identify the entities.The first step in making an ERD is to identify all of the entities you will use. An entity is
nothing more than a rectangle with a description of something that your system stores information about. This
could be a customer, a manager, an invoice, a schedule, etc. Draw a rectangle for each entity you can think of
on your page. Keep them spaced out a bit.
ERD Boxes
Identify relationships.Look at two entities, are they related? If so draw a solid line connecting the two entities.
Describe the relationship.How are the entities related? Draw an action diamond between the two entities on the
line you just added. In the diamond write a brief description of how they are related.
Identify the cardinality. Identify the cardinality between the two entities. Is it one-to-one? Many-to-many?
Add attributes.Any key attributes of entities should be added using oval-shaped symbols.
Complete the diagram.Continue to connect the entities with lines, and adding diamonds to describe each
relationship until all relationships have been described. Each of your entities may not have any relationships,
some may have multiple relationships. That is okay.
Tips for Effective ER Diagrams
Make sure that each entity only appears once per diagram.
Name every entity, relationship, and attribute on your diagram.
Examine relationships between entities closely. Are they necessary? Are there any relationships missing?
Eliminate any redundant relationships. Don’t connect relationships to each other.
Use colors to highlight important portions of your diagram.
Understanding Cardinality
Cardinality specifies how many instances of an entity relate to one instance of another entity and specifies the
occurrences of a relationship. In other words, cardinality specifies the maximum number of relationships
between two entities. The diamond need to describe what action is taking place not necessarily what decision
is being made (they could be the same thing. Below is an example:
Cardinality
Lastly, the internet has a plethora of examples for ERDs. Feel free to look around to get a feel for how to best
represent your system on an ERD.
*Please use attached documents for reference as to what kind of information to use, the description of my
system in included*