DBMS Models defines the logical design and structure of a database and defines how data will be stored, accessed and updated in a database management system. There have been few proposed models which were used & then due to limitations in each of them . They got replaced by new DBMS Models. Most widely used and popular of them all is relational database model.
- Hierarchical database
- Network database
- Entity Relationship Data Model
- Relational Database Model.
Hierarchical Data Model :
Hierarchical Data Model has a tree like relationship between data. If you see the diagram below , You can see that we have a root at the top , root being the starting point you can also call it the Parent . In this model data is present in such a way that one data item is present as the children of its above one. Which means , that there is a child parent relationship between data items.
One-To-Many relationship exists between data items, which means a parent can have many children , but children will have only one parent. Only movement between data items , is moving downwards .
Hierarchical Data Model has a huge disadvantage , you cannot enter the data in a child without entering it first into it’s parent ( Because of parent-child relationship) . Why is it bad? Because this creates data redundancy problems which affects the performance and efficiency of system.
Network Database Model :
This model looks a lot like hierarchical model , which is understandable as it is driven from later for better results. Here , data items have many-to-many relationships between them , which mean a child can have more than one parent if needed be.
let’s try to understand the diagram below ,
Taking a real-life example , for a store if we try to apply a hierarchical model child , it will create a strict and complex relationship to handle orders , since orders cannot have more than one parent in that model. Network model , solved this problem , as orders now have more than one parents.
This solution was better than it’s predecessor but it also created a much complex structure to maintain and handle as the system grow . The brightest minds in world then came up with a best solution to the problems . This model is in extensive use all over the world.
Entity Relationship Data Model
Entity Relationship Data Model is designed by translating real-world scenarios into database model by creating entities , relationships , attributes and constraints. All of these terms have detail articles. Click the above links for details. This is a conceptual diagram of a database . Designer creates entities , attributes and define relationships between them and constraints to manage them
Read a complete article on E-R Model and entity diagram.
Relational Database Model
In late 1960’s a mathematician Dr. E. F. Codd came up with another data model , which handled and removed the limitations of existing models. This model is based on concepts of maths and set theory.
Data items consisted of tables ( also called relation ) attributes-members-represented in columns and rows to handle and stored the data. It’s a lot like a spreadsheet but you can create one-to-one , one-to-many and many-to-many relationships between tables .
Dr. Codd also gave 12 rules , which were followed ever since to create relational databases. The relationships that can be created among the tables enable a relational database to efficiently store huge amount of data, and effectively retrieve selected data. A SQL (Standard Query Language ) was developed to work with relational database.
Confused with the last diagram? Check this article on how to read Crow’s Foot Notation .
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