MySQL Workbench 中的 ER 图是关系模型吗？

Question

Im trying to understand this situtation. What is the difference between ER and Relational Model for mysql. It looks like relational model more than an actual ERD on MySQL so why is it called ER than ?

Answer 1

The ER model and relational model aren't MySQL specific. They're used for conceptual and logical modeling, respectively. A SQL or MySQL-specific model would be called a physical model.

The diagrams in MySQL Workbench (and many similar tools) are physical models which abuse ER terminology. It allows one to design tables, columns, primary keys, foreign key constraints and indices. It doesn't distinguish between entity tables and relationship tables as the ER model does, but calls all tables entities and confuses relationships with foreign key constraints. Thanks to this, the idea of n-ary relationships is lost and users are led back to network model databases.

They're not relational data models either. They don't capture logical domains or roles, functional or multivalued dependencies, or various constraints. They don't support dependency-preserving transformations.

The difference between the ER and relational model is that the relational model has the full power of first-order logic while the ER model is more of a recipe approach. ER semantics are more familiar to the untrained eye, but add extra complexity. There are some dependencies and constraints that can't be represented in ER, and its focus on 3NF may result in data anomalies. Despite that, it's useful for initial/informal data modeling and to communicate ideas to business users.

So why are diagrams like those in MySQL Workbench called ER diagrams then? I think it's mostly due to lack of understanding and buzzword compliance, two factors that are rife in our industry.

Answer 2

ER Diagram is a visual representation of the Database. It is the primary level of designing a good database. we use ER diagram to identify the entities and relations. later entities became as TABLE and relations may became as Foreign keys. it is a transforming process ERD ---> Relational MODEL Relational model is complex. we can achieve the Relational model using ER Diagram. ER diagram to Relational model