An entity connection diagram, according to Bagui and Earp (2012), is a semantic data modeling tool used in abstractly defining or portraying data, hence providing a conceptual representation of the underlying data. As a result, ERDs are critical in assisting business analysts in understanding the business domain, clarifying diverse business language, and connecting various business concepts to database structures.
Entity relationship diagrams, according to Hadzic, Chang, and Wongthongtham (2014), are made up of three basic components: entities, characteristics, and relationships. Entities on the one hand describe objects or concepts in which information is stored while attributes on the other hand uniquely distinguish entities while providing more detailed information about them. Once entity diagrams with their unique attributes are developed, the association between different entities is represented by relationships which link them together (Captain, 2013).
Bagui & Earp (2012) further add that when representing ER diagrams, different shapes are suitably used. Entities are represented using rectangles while their different attributes are represented as fields within them. On the other hand, relationships between the different entities are represented using diamond shapes with the given association linking the different diagrams described. Further, it is also important to note that the various instances an entity can relate to another is described as its cardinality while the description of whether the such relationships are either mandatory or optional is referred to as its ordinality (Captain, 2013). In addition, various notation styles are employed in expressing the cardinality and ordinality of relationships such as the information engineering style, used with crow’s foot notation, Chen style and Bachman style.
In the current blogging database project, three entities are identified: user accounts, articles and groups.
Entity: User accounts
Attributes contained include: user_email_address, user_password, first name, last name and alternatively, personal information such as gender.
Relationships include: users create articles in many to many relationships where many users can create many articles. Secondly, users can also create groups in many to many relationships where many users can create many groups.
Articles
Attributes contained include: title, content, date created, date edited, group, comments, and status (i.e., whether the article is ready to be published or not).
Relationships include: articles can be assigned to particular groups in either a one to many relationships where one article is assigned to many groups or a many to many relationships where many articles are assigned to many groups. Articles are also created by the different user accounts.
Groups
Attributes contained include: group_name and group_id, and group_members
Relationships include: users can create different groups in a many to many relationships where many users can create many groups. Similarly, articles are assigned to groups on a many to many bases where many articles can be assigned to many groups.
The ERD diagram is shown in figure 1 below:
Figure 1: Entity Relationship diagram
As the diagram illustrates, users who joins XYZ blogs are able to create many articles which can then be assigned to many groups. Similarly, the users are able to create many groups and define members for the groups.
References
Bagui, S., & Earp, R. (2012). Database design using entity-relationship diagrams. Boca Raton, FL: CRC Press.
Captain, F. (2013). Six-step relational database design (2nd ed.). British Virgin Islands: Fidel A Captain.
Hadzic, M., Chang, E., & Wongthongtham, P. (2014). Ontology-Based Multi-Agent Systems. Berlin: Springer Berlin.
