-


DBMS Database Models

A Database model defines the logical design and structure of a database and defines how data will be stored, accessed and updated in a database management system. While the Relational Model is the most widely used database model, there are other models too:
  • Hierarchical Model
  • Network Model
  • Entity-relationship Model
  • Relational Model

Hierarchical Model

This database model organises data into a tree-like-structure, with a single root, to which all the other data is linked. The heirarchy starts from the Root data, and expands like a tree, adding child nodes to the parent nodes.
In this model, a child node will only have a single parent node.
This model efficiently describes many real-world relationships like index of a book, recipes etc.
In hierarchical model, data is organised into tree-like structure with one one-to-many relationship between two different types of data, for example, one department can have many courses, many professors and of-course many students.
Hierarchical Model of database

Network Model

This is an extension of the Hierarchical model. In this model data is organised more like a graph, and are allowed to have more than one parent node.
In this database model data is more related as more relationships are established in this database model. Also, as the data is more related, hence accessing the data is also easier and fast. This database model was used to map many-to-many data relationships.
This was the most widely used database model, before Relational Model was introduced.
Network Model of database

Entity-relationship Model

In this database model, relationships are created by dividing object of interest into entity and its characteristics into attributes.
Different entities are related using relationships.
E-R Models are defined to represent the relationships into pictorial form to make it easier for different stakeholders to understand.
This model is good to design a database, which can then be turned into tables in relational model(explained below).
Let's take an example, If we have to design a School Database, then Student will be an entity with attributes name, age, address etc. As Address is generally complex, it can be another entity with attributes street name, pincode, city etc, and there will be a relationship between them.

E-R Model of database

Relational Model

In this model, data is organised in two-dimensional tables and the relationship is maintained by storing a common field.
This model was introduced by E.F Codd in 1970, and since then it has been the most widely used database model, infact, we can say the only database model used around the world.
The basic structure of data in the relational model is tables. All the information related to a particular type is stored in rows of that table.
Hence, tables are also known as relations in relational model.

Comments

Post a Comment

Popular posts from this blog

-
Image
CLUSTERED INDEX VS NON CLUSTERED INDEX Clustered Index Only one clustered index can be there in a table because of the sorted order Sort the records and store them physically according to the order Data retrieval is faster than non-clustered indexes Do not need extra space to store logical structure A primary key by default creates a clustered index on it. Non Clustered Index There can be any number of non-clustered indexes in a table because of the number of unique keys we can create. Do not affect the physical order. Create a logical order for data rows and use pointers to physical data files Data insertion/update is faster than clustered index Use extra space to store logical structure A unique key/keys by dafault created an unclustered index on it. In Depth Explanation: Clustered Technically speaking, a clustered index is a B-Tree data structure where all the rows in a table are stored at the leaf level of the index. In other words, a clustered ind...
Read more
-
Image
SQL JOINS Tutorial: INNER, OUTER, LEFT, RIGHT, CROSS What are JOINS? Joins help retrieving data from two or more database tables. The tables are mutually related using primary and foreign keys. id first_name last_name movie_id 1 Adam Smith 1 2 Ravi Kumar 2 3 Susan Davidson 5 4 Jenny Adrianna 8 6 Lee Pong 10 id title category 1 ASSASSIN'S CREED: EMBERS Animations 2 Real Steel(2012) Animations 3 Alvin and the Chipmunks Animations 4 The Adventures of Tin Tin Animations 5 Safe (2012) Action 6 Safe House(2012) Action 7 GIA 18+ 8 Deadline 2009 18+ 9 The Dirty Picture 18+ 10 Marley and me Romance   Types of joins Cross JOIN Cross JOIN is a simplest form of JOINs which matches each row from one database table to all rows of another. In other words it gives us combinations of each row of first table with all records in second table. Suppose we want to get all member records against all the movie records, we can use the script shown below to ge...
Read more
-
Image
COMMON TABLE EXPRESSIONS(cte): It is used best used to extract the hierarchical data  and it is best explained with an example: Problem Many organizations have some type of hierarchy for business processes. When it comes to large organizations, the hierarchy can get very complex and large, so building a hierarchy in a RDBMS is a tedious task. We have to create views, cursors and so on, but using a CTE in SQL Server is a better solution to retrieve hierarchy-based data. Solution Common Table Expressions (CTE) have two types, recursive and non-recursive. We will see how the recursive CTE works with examples. A recursive CTE can be explained in three parts: Anchor Query: This is the first statement which is executed. This query will give the base data for the CTE. Separator: This is the middle part where in we generally use a UNION ALL and few more operators. Recursive Query: This is the main part, this is the CTE query which refers to the same CTE by recursion. ...
Read more