Rdbms Unit_I_II

Unit-I		Unit-II	Unit-III	Unit-IV	Unit-V
Part-I	Part-II	Part-I	Part-I	Part-I	Total
Part-III	Part-IV	Part-II	Part-II	Part-II
Part-V		Part-III

 8.Explain the types of Databases?

Ans:

Types of Databases

 

Databases can be classified according to the number of users, the database location(s), and the expected type and extent of use.

 

Number of users

A single-user database supports only one user at a time.

A multiuser database supports multiple users at the same time.

Workgroup database

When the multiuser database supports a relatively small number of users  or a specific department within an organization, it is called a workgroup database.

Enterprise database

When the database is used by the entire organization and supports many users  across many departments, the database is known as an enterprise database.

Location of database

Centralized database

A database that supports data located at a single site is called a centralized database.

Distributed database

A database that supports data distributed across several different sites is called a distributed database.

 

The expected type and extent of use

Operational database

A database that is designed primarily to support a company’s day-to-day operations is called as an operational database .

Data warehouse

A data warehouse focuses primarily on storing data used to generate information required to make tactical or strategic decisions.

Relational and er Models

9. Explain About Various Data Models?

Ans:

Data model

A Data model is a integrated collection of concepts for describing and manipulating data, relationships between data, and constraints on the data in an organization.

The purpose of a data model is to represent data and to be understandable.

 

The data models  are 3 categories:

1.     Object-Based Data Models

2.     Record-Based Data Models

Physical Data Models

Object-Based Data Models

Object-based data models use concepts such as entities, attributes, and relationships.

An entity is a distinct object (a person, place, thing, concept, event) in the organization that can be represented in the database. An attribute is a property that describes some aspect of the object that we wish to record.

A relationship is an association between entities.

Some  object-based data model are:

• Entity-Relationship (ER)

• Semantic

• Functional

• Object-oriented

Entity-Relationship (ER) is the main technique used for database design.

Record-Based Data Models

The database consists of a number of fixed-format records. Each record type defines a fixed number of fields.

These are three types:

1.     The Relational Data Model

2.     The Network Data Model

3.     The Hierarchical Data Model.

Relational data model

In the relational model, data and relationships are represented as tables, each of which has a number of columns with a unique name.

Figure (a) is a example of DreamHome case study, showing branch and staff  details. For example, it shows that employee John White is a manager with a salary of £30,000, who works at branch (branchNo) B005, which, from the first table, is at 22 Deer Rd in London. It is important to note that there is a relationship between Staff and Branch: a branch office has staff.

Network data model

In the network model, data is represented as collections of records, and relationships are represented by sets.

The records are organized as generalized graph structures with records appearing as nodes (also called segments) and sets as edges in the graph. 

Hierarchical data model

The data is represented as collections of records and relationships are represented by sets. The hierarchical model allows a node to have only one parent. A hierarchical model can be represented as a tree graph, with records appearing as nodes (also called segments) and sets as edges.

The main hierarchical DBMS is IBM’s IMS

Physical Data Models

Physical data models describe how data is stored in the computer, representing information such as record structures, record orderings, and access paths. The most common ones are the unifying model and the frame memory.