Types of DBMS

Types of Database Management Systems:

Over the years, to satisfy the needs of data storage, processing and retrieval, database models of varying degrees of sophistication were devised. Large enterprises needed to build many independent data files containing related and even overlapping data, often in quite different formats to fulfill different purposes. Data-processing activities frequently required the linking of data from several files necessitating designing data structures and database management systems that supported the automatic linkage of files. Four database models and their corresponding management programs were developed to support the linkage of records of these types. The following database models and their management systems are in common use:

1.     Hierarchical databases.

2.     Network databases.

3.     Relational databases.

4.     Object-oriented databases

1. Hierarchical Database Management System:

A hierarchical database is a one in which the data elements have a one-to-many relationship (1:N). The schema for a hierarchy has a single root. This kind of database model uses a tree-like structure which links a number of dissimilar elements to one primary record – the "owner" or "parent". Each record in a hierarchical database contains information about a group of parent child relationships. The data are stored as records, each of which is a collection of fields containing only one value. The records are connected to each other through links. The structure implies that a record can have a data element repeated. Hierarchical models make the most sense where the primary focus of information gathering is on a concrete hierarchy such as a list of business departments, assets or people that will all be associated with specific higher-level primary data elements. They are very simple and fast. In the hierarchical database model the user must have some prior information about the database. Hierarchical databases were popular in early database design, in the era of mainframe computers.

   2. Network Database Management System:

A network database model is one in which multiple member records or files are linked to multiple owner files and vice versa. The network database model can be viewed as a net-like form where a single element can point to multiple data elements and can itself be pointed to by multiple data elements.

The network database model allows each record to have multiple parents as well as multiple child records, which can be visualized as a web-like structure of networked records. By contrast, in the hierarchical model, a data member can only have many child records, but only a single parent record.

Actually, the network model is quite similar to the hierarchical model – the hierarchical model being a subset of the network model. However, instead of using a single-parent tree hierarchy, the network model uses set theory to provide a tree-like hierarchy with the exception that child tables are allowed to have more than one parent. It supports many-to-many relationships and can be visualized as a cobweb or interconnected network of records.

  3. Relational Databases Management System:

A relational database is one in which data is stored in the form of tables, using rows and columns. This arrangement makes it easy to locate and access specific data within the database. It is “relational” because the data within each table are related to each other. Tables may also be related to other tables. In relational databases, tables or files containing data are called relations (tuples), and are defined by rows (or records), and columns (or attributes) referred to as fields. Each table has a key field that mainly identifies each record (row), and on the basis of which records in different tables are related (or linked).

This kind of a relational structure makes it possible to run queries that need to retrieve data from multiple tables simultaneously. An RDBMS may also provide a visual representation of the data. For example, it may display data in a spreadsheet-like table, allowing you to view and even edit individual data elements in the table. Some RDMBS programs allow you to create forms that can streamline entering, editing, and deleting data. Most well-known database management systems fall into the RDBMS category. Examples include Oracle Database, MySQL, Microsoft SQL Server, and IBM DB2. Some of these programs support non-relational databases, but they are primarily used for relational database management.

Currently, the relational database approach is the most popular. The older hierarchical data management systems are being replaced by relational database management. Relational DBMS software is available for large mainframe systems as well as workstations and personal computers. The need for more powerful and flexible data models to support scientific and business applications has led to extended relational data models in which table entries are no longer simple values but can be programs, text, unstructured data in the form of large binary, or in any other format which the end user needs.

  4. Object-Oriented Database Management System:

A recent development in database technology is the incorporation of the object concept that has become significant in programming languages. In object-oriented databases, all data are objects. Objects may be linked to each other by an “is-part-of” relationship to represent larger, composite objects. For example, the data describing a truck may be stored as a composite of a particular engine, chassis, gear box, steering system, etc. Classes of objects may form a hierarchy in which individual objects may inherit properties from objects higher up in the hierarchy. For example, objects of the class “motorized vehicle” will all have an engine (a truck, a car or an airplane). Likewise, engines are also data objects, and the engine attribute of a particular vehicle will be a link to a specific engine object. Multimedia databases, in which voice, music, and video are stored along with the traditional textual information, provide a justification for viewing data as objects. Such object oriented databases are becoming increasingly important, since their structure is most flexible and adaptable. The same is true of databases of pictures, images, photographs or maps. The future of database technology is generally perceived to be an integration of the relational and object-oriented database models.