Types of Database Models
Database is an organized collection of information or data, records arranged. A database model is a type of data model that defines a Database’s logical structure. It also defines how the data can be stored, organized, and manipulated in the first place. In DBMS, there are mainly five types of database models.
Types of Database Models in DBMS:
Generally, five types of database models in DBMS:
1. Hierarchical DBMS (HDBMS)
2. Network DBMS (NDBMS)
3. Relational DBMS (RDBMS)
4. Object-Oriented Database (OODB)
5. Distributed DBMS (DDBMS)
Hierarchical Model in DBMS:
Hierarchical data model developed by IBM in 1968 and it introduced in IMS (Information Management System). This model is like a structure of a tree with the records forming the nodes and fields forming the branches of the tree. In this model, records are linked in the form of an organisational chart
Advantages of Hierarchical Model:
(i) It is a simple, straightforward and natural method of implementing record relationships.
(ii) Hierarchical model is useful when there is some hierarchical character in the database.
Disadvantages of Hierarchical Model:
(i) The hierarchical model can’t represent all the relationships that occur in the real world.
(ii) It can’t demonstrate the overall data model for the enterprise because of the non-availability of actual data at the time of designing the data model.
(iii) The hierarchical model is used only when there is a hierarchical character in the concerned database. It can’t represent many to many relationship (M:M)
(iii) Insert Anomaly: It is not possible to insert data about a new dependent. If its superior record is not present, a node can’t exist without a root.
(iv) Delete Anomaly: Deletion operation in a hierarchical database leads to loss of many necessary information.
(v) Update Anomaly: Updation operation in a hierarchical database leads to several inconsistencies in the database.
Network Model in DBMS:
In network database structure, a record type can have multiple owners. In the network model, the data is represented by records using links among them. It is an improvement over the hierarchical model, here we can have many too many relationships (M: M) among records.
Advantages of Network Model:
(i) Network model is useful for representing such records which have many to many relationships (M:M) .
(ii) Problem of inconsistency does not exist in a network model because a data element is physically located in just one place.
(iii) Searching a record is easy since there are multiple access paths to a data element.
Disadvantages of Network Model:
(i) All records are maintained using pointers and hence the whole database structure becomes very complex.
(ii) Insertion, deletion and updation of any record would require pointer adjustments.
Relational Model in DBMS:
In a Relational Database Model, the data organized in the form of rows and columns similar to a table. The tables are referred to as relations in a relational data model. The rows of the table are referred to as tuples and the columns of a table are referred to as attributes. A relational database model is defined as a database that allows you to group its data items into one or more independent tables. They can be related to one another by using fields common to each related table.
Advantages of Relational Model:
(i) The relational database structure can be efficiently used even with a PC that has limited main memory and processing capability.
(ii) Relational database is much easier to use because it enables a computer system to accommodate a variety of enquiries efficiently.
(iii) Relational database is very effective for small database.
(iv) Relational database is only concerned with data and not with the structure, which improves the performance.
(v) Network and Hierarchical database use pointers to implement record relationship. But in relational database record relationship implemented by using primary key or composite key fields.
(vi) Relational model is very useful for representing most real-world objects and the relationships among them.
Object-Based Data Model in DBMS:
Object Oriented Database (OODB) are dependent on the object-oriented programming paradigm. It enables us to create classes, organize objects, structure, an inheritance hierarchy and call methods. It represents the class-subclass links. The dash ( – – – – ) represents attribute-domain link.
Advantages of Object-Based Data Model:
(i) OODB allows nested structure. So it is easier to navigate through these complex structures in the form of objects rather than in the form of tables and records.
(ii) OODB allows arbitrary data types and sub-classing with inheritance.
(iii) OODB is favoured in those applications where the relationship among data elements. It is more important than the data items themselves.
Distributed Database in DBMS:
In the centralized database system, data stored or resides in one single location. But in a distributed database system, database stored in several computers.
The computers in a distributed system communicate and exchange data with one another using leased lines, telephone lines or other means of communication. These computers do not share a memory or a clock. Each of the computers in a distributed system participates in the execution of transactions. These computers say sites or nodes.