Database: A Database is a collection of inter-related data from which some information can be extract.
Database Management System (DBMS)
Database Management Systems organize and structure data so that it can be retrieved and manipulating by users and application programmer.
Database Model: The data structures and access techniques provided by a particular DBMS are called as Data Model.
Hierarchical data model:
- This model is like a hierarchical tree structure; used to construct a hierarchy of records in the form of nodes and branches. The data elements presnt in the structure of parent/ child relationship.
- Every child has one parent.
- You can see only one record at a time.
- Retrieving the data in a Hierarchical database thus required navigating through the records,
Moving up, down, sideways one record at a time.
- Example Windows Explorer
- Developed By IBM Named as Information Management System (IMS) in 1968
The Drawback of Hierarchical data model
- It cannot handle a large data
- It’s not support many to many to relation
Network data model
- The simple structure of a Hierarchical database became a disadvantage when the data had a more complex structure. In an order-processing database, for example, a single order might participate in three different parent/child relationships, linking the order to the customer who placed it, the salesperson who took it, and the product ordered.
The Network model extended the Hierarchical model by allowing a record to participate in multiple parent/child relationship
Network databases had their disadvantages like Hierarchical database, they where very rigid. The set relationships and the structure of the records had to be specified in advance.
The Drawback of Network data model
- Changing the database structure typically required rebuilding the entire database.
* Data is organized in terms of rows and columns in a table knowns as relations
* The position of a row in a table is of no importance.
* The intersection of row and column must give a single value and not a set of values.
* Column name must be unique
* Row must be unique
* It eliminated the explicit parent/child structures from the database, and instead of represented all data in the database as simple row/column tables of data values.
* A relational database is a database where all data visible to the user is organized strictly as tables of data values, and where all database operations work on these tables.
The publication of the paper “A relational Model of Data for Large Shared Database” by Dr. E.F. Codd in June 1970 in the “Communication of ACM” , set a trend for virgorous and extensive investigation into a theoretical frame work to support further work in the area of Data Modelling. The end result is the Relational Database Management System.