RDBMS In-Depth: Mastering SQL and PL/SQL Concepts, Database Design, ACID Transactions, and Practice Real Implementation of RDBM (English Edition)

An entity-relationship model is data driven. The model implies processes but does not clarify the processes.

Used with data flow diagrams under structured approach, an entity-relationship model gives the analyst an alternative logical view of the system. If a great deal is known about the data, but not much about the processes, an entity-relationship diagram is an excellent start point for modelling the system.

Armstrong’s Axioms are a set of rules, that when applied repeatedly, generates a closure of functional dependencies. The functional dependency (FD) is a relationship between two attributes, typically between the primary key and other non-key attributes within a table.

Armstrong axioms refer to the sound and complete set of inference rules or axioms, introduced by William W. Armstrong, that is used to test the logical implication of functional dependencies.

A relation is a data structure which consists of a heading and an unordered set of tuples (rows). In databases, a table is a set of data elements (values) that is organized using a model of vertical attributes and horizontal tuples which share the same type.

However, in Database Management System, there are no relationships among tables. In 1970s, Edgar Frank Codd introduced the theory of relational database. 12 rules were defined by Codd for this relational theory or model which we discussed in the 2nd chapter.

The columns, LectTim and LectDay will be dependent attributes, as this is a rule in a many-to-many relations, that the intermediate table will always have the dependent attributes which are dependent on both the entities.

This is referential integrity rule, which allows the user to delete rows from the master, and at the same time it will delete the dependent rows in all the child tables.

This is referential integrity, which ensures that there are no rows in the transaction (CHILD) table if there is no reference row present in the master (PARENT) table.

Now the question is, is it possible that student_marks contain a row for roll number 10?
No, it is not possible and that is because roll number 10 does not exist in the student master table or there is no reference for that number in the PARENT table.