Instructions for Skills Practice – Conceptual ERD
Assignment
Create a conceptual data model for the iSchool Webstore System expressed as an
Entity-Relationship diagram (ERD). To accomplish this, I recommend the following
process:
1. Identify the entity types that are needed in the data model for the iSchooI
Webstore System domain. Use the Visio 2013 diagrammer to create a block for
each entity type. If you know the attributes for the entity type, you can enter
them at this time. Otherwise, you can defer this work until Step 3 in the process.
2. Identify the relationships that exist between entity types. Use the diagrammer
to draw relationship lines between entity type blocks. Give each relationship a
descriptive name. Finally, determine the cardinalities of the relationship and
record the cardinalities at each end of the relationship line using crow’s foot
notation.
3. For each entity type, record the various attributes that will hold the information
about that entity in the data model. Using the diagrammer, record each
attribute on its own line within the entity type block. Finally, note the attributes
that will be used to make up an identifier for each entity type. Use the
diagrammer’s PK notation to mark each attribute that makes up the identifier.
PK stands for ”primary key”. PK is actually a relational database term rather than
a conceptual data model term. But it is the best diagrammer feature that you
can choose to indicate components of the identifier for each entity.
4. Look for any relationships that carry data. An example of this would be the
quantity of items that must be carried in each Order-Item relationship.
Wherever a data must be carried in a relationship, insert an associative entity to
carry the data. This will result in two relationships with an intervening
associative entity.