What ia an ERD. Define the RED related terms, including entities, attributes, cardinalities and relationships

 

The acronym "entity-relationship diagram," or ERD for short, refers to a graphical depiction of entities and the interactions between them. ERDs are a typical tool used in the architecture of databases to represent the connections that exist between various tables and the characteristics that they include.

The things or ideas inside a database that are being modelled are referred to as entities. In a database designed for a library system, some examples of entities that could be included include books, borrowers, and loans. Each entity has attributes that provide a description of the traits it possesses. As an example, some of the qualities that might be associated with the book entity are the book's title, author, and release date.

The number of instances of one entity that may be connected to instances of another entity is referred to as its cardinality, and cardinalities are used to define the connections that exist between things. The concept of cardinalities is often conveyed via the use of symbols such as one-to-one (1:1), one-to-many (1:N), and many-to-many (M:M) (N:M). For instance, in a database maintained by a library, the connection between books and borrowers may be described as one-to-many. This would mean that a single book might be checked out by several borrowers at the same time, but each borrower could only check out a single book at a time.

A database's relationships may be used to explain the linkages that exist between any number of different elements. Several kinds of connectors, such lines or arrows, may be used to depict various kinds of relationships. These connectors are named to show the nature of the link that they represent. For instance, if a book may be borrowed by a borrower, the connection between the book and borrower entities could be characterised as "borrowed by." This would show that a borrower has access to the book.

In general, ERDs are a powerful tool that may be used to visualise and create complicated databases. They provide assistance in identifying entities, as well as their qualities and the interactions that exist between them, which may be essential in the process of developing database designs that are both effective and efficient.

References:

Chen, P. P. (1976). The entity-relationship model—toward a unified view of data. ACM Transactions on Database Systems (TODS), 1(1), 9-36.

Connolly, T., & Begg, C. (2014). Database systems: a practical approach to design, implementation, and management. Pearson.

Elmasri, R., & Navathe, S. B. (2010). Fundamentals of database systems. Pearson.