Hello, and welcome to Information Models and Data Models.
In this video we will learn about different types of models.
At the end of this video,
you will be able to describe the difference between
an information model and a data model.
Explain the advantage of the relational model,
and describe the difference between an entity and an attribute.
This figure illustrates the relationship between an information model and a data model.
An information model is
an abstract formal representation of entities that includes their properties,
relationships, and the operations that can be performed on them.
The entities being modeled can be from the real world,
such as a library.
Information models and data models are different and serve different purposes.
An information model is at
the conceptual level and defines relationships between objects.
Data models are defined in a more concrete level,
are specific and include details.
A data model is the blueprint of any database system.
There are several types of information models.
The most familiar is the hierarchical,
typically used to show organization charts.
As shown in this figure,
the hierarchical model organizes its data using a tree structure.
The root of the tree is the parent node followed by child nodes.
A child node cannot have more than one parent.
However, a parent can have many child nodes.
The first hierarchical database management system was
the information management system released by IBM in 1968,
and was originally built as the data base for the Apollo space program.
The relational model is the most used data model for databases,
because this model allows for data independence.
Data is stored in simple data structure tables.
This provides logical data independence,
physical data independence, and physical storage independence.
An entity-relationship data model or ER data model,
is an alternative to a relational data model.
Using a simplified library database as an example,
this figure shows an Entity Relationship Diagram or ERD,
that represents entities called tables and their relationships.
We have authors who write books,
borrowers who take books out on loan,
various copies of each book etc.
This is the final ER diagram. But how do we get there?
An entity-relationship model proposes thinking of a database as a collection of entities,
rather than being used as a model on its own.
The ER model is used as a tool to design relational databases.
In the ER model,
entities are objects that exist independently of any other entities in the database.
It is simple to convert an ER diagram into a collection of tables.
The building blocks of an ER diagram are entities and attributes.
Entities have attributes, which are the data elements that characterize the entity.
Attributes tell us more about the entity.
In an ER diagram, an entity is drawn,
as a rectangle, and attributes are drawn as ovals.
Entities can be a noun,
person, place, or thing.
Using a simplified library as an example,
a book is an example of an entity.
Attributes are certain properties of characteristics of an entity,
and tell us more about the entity.
The Entity book has attributes such as the book title,
the addition of the book,
the year the book was written etc.
Attributes are connected to exactly one entity.
The entity book becomes a table in the database,
and the attributes become the columns in a table.
Continuing the simplified library example,
books are written by authors,
book is an entity,
an author is an entity.
For the entity author,
the ER diagram would look like this.
The entity author has attributes,
such as the author's last name, first name,
email, city, country, and an author ID to uniquely identify the author.
The entity author becomes a table in the database,
and the attributes become the columns in the table.
In the simplified library database,
we progress through the process of identifying entities,
such as borrowers who take books out on loan,
various copies of each book,
and copies of books out on loan.
This is the final ER Diagram.
Each entity becomes a table in the database.
You can now describe the difference between an information model and a data model,
explain the advantage of the relational model,
and describe the difference between an entity and an attribute.
Thanks for watching this video.
