Types of DBMS
A database is an organized collection of information or data, records arranged and presented to serve an assigned purpose. Various types of DBMS are given as follows :
1. Hierarchical DBMS (HDBMS) :
Hierarchical data model was developed by IBM in 1968 and it is 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 organization chart
Advantages of Hierarchical DBMS 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 DBMS Model :
(i) The hierarchical model can’t represent all the relationships that occur in the real world.
(ii) It can’t demonstrate the over all 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, because 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.
2. Network DBMS (NDBMS) :
In network database structure, a record type can have multiple owners. In network model, data are represented by records using links among them. It is an improvement over the hierarchical model, here we can have many to many relationships (M:M) among records.
Advantages of Network DBMS 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 at just one place.
(iii) Searching a record is easy since there are multiple access paths to a data element.
Disadvantages of Network DBMS 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.
3. Relational DBMS (RDBMS) :
In a Relational Database Model, data is organized in the form of rows and columns similar to a table. The tables are referred to as relations in a relational data model. 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 that can be related to one another by using fields common to each related table.
Advantages of Relational DBMS 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 in an efficient manner.
(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 is implemented by using primary key or composite key fields.
(vi) Relational model is very useful for representing most of real world objects and the relationships among them.
4. Object Oriented Database (OODB) :
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 of represents class-subclass link. The dash ( – – – – ) represents attribute-domain link.
Advantages of OODB 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 are favoured in those applications where the relationship among data elements are more important than data items themselves.
5. Distributed DBMS (DDBMS) : In the centralized database system, data stored or resides in one single location, but in a distributed database system, database is stored in several computers. The computers in a distributed system communicate and exchange data among 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 can also be known as sites or nodes.