I was asked to draw the ERD and relational diagram of a table, I previously assumed that the relational diagram was the same as a ERD so what is the difference?
2 Answers
An Entity Relationship Diagram defines the relationship between entities and their attributes. In example, an ERD contains many-to-many relationships and do not include foreign keys. They are implied. In an ERD, we are simply visualising the entities, their attributes, and the relation between them. we dont care about where foreign keys go or how to implement that many-to-many relationship. (but we do underline primary keys!)
In a Relational Model we are referring to an implementation of our model. At this point we should be clear about the formats of our attributes, the foreign keys we use, and the linking tables we might need to stitch entities together. A relational model is basically a model of a possible database implementation.
In short, an ERD is an abstract concept of our database, it speaks in entities and attributes, an entity model. A relational model defines formats and relations in a way a database could understand, a data model.
ERD is belongs to relationship between entities, it is different from relation model.
Relational Database: A database that maintains a set of separate, related files (tables), but combines data elements from the files for queries and reports when required.
Relational model concepts are as follows:
ERD: A database model that describes the attributes of entities and relationship occurs between two or more entities.
