1. What is a relational database management system (RDBMS)?
    A relational database management system (RDBMS or just RDB) is a common 
    type of database that stores data in tables, so it can be used in relation 
    to other stored datasets. Most databases used by businesses these days are 
    relational databases, as opposed to a flat file or hierarchical database. 
    The majority of current IT systems and applications are based on a relational DBMS.


2. What is SQL?
    SQL stands for Structured Query Language. A query language is a kind of programming
    language that's designed to facilitate retrieving specific information from databases, 
    and that's exactly what SQL does. To put it simply, SQL is the language of databases.


3. What is an ER model?
    An Entity Relationship (ER) Diagram is a type of flowchart that illustrates how entities
    such as people, objects or concepts relate to each other within a system. ER Diagrams are 
    most often used to design or debug relational databases in the fields of software engineering, 
    business information systems, education and research.


4. Define the following terms: One-to-one relationship, one-to-many relationship, and many-to-many 
    relationship. 
    1-1 = ne-to-one relationship is a type of cardinality that refers to the relationship 
    between two entities A and B in which one element of A may only be linked to one 
    element of B, and vice versa.

    1-Many = one-to-many relationship is a type of cardinality that refers to the relationship between 
    two entities A and B in which an element of A may be linked to many elements of B, but a member
    of B is linked to only one element of A.

    Many-Many = many-to-many relationship is a type of cardinality that refers to the relationship 
    between two entities A and B in which A may contain a parent instance for which there are 
    many children in B and vice versa.

5. What is the purpose of a primary key? Why should it be unique?
    A primary key is used to refrence a row in a column. It is importatn for it to be unique because
    if it wasnt the same key would fetch multiple rows.