data abstraction

The standard database structure consisting of conceptual , external and internal levels . In three schema architecture have three levels of abstraction at which a database could be viewed. These three levels are .... for more details u may get please visit http://www.database-concept.com/

DBMS Musings: Replication and the latency-consistency tradeoff

DBMS Musings: Replication and the latency-consistency tradeoff: As 24/7 availability becomes increasingly important for modern applications, database systems are frequently replicated in order to stay up ...

database models

DATA MODELS

Data model is a collection of logical constructs used to represented to data structure and data relationships found with in the databases . Database models can be grouped into two (2) categories. These are

1. Record based logical model  (or) implementation model.
2. Object based  logical model (or) conceptual model.
3. E-R (Entity – Relationship ) model.

Record based logical model / Implementation model: This model emphases on how the data are represented in the database. It has 3 (three) types. These are

1. Hierarchical data model.
2. Network data model.
3. Relational data model.

Hierarchical data model  we can represent the data as a tree model . The origin of data tree is the root . The data is located at different level along a particular branch from the root is called  is node . the last node in the series is called leaf . It supports one-to-many relationship.

 

 The main idea behind Network data model   is to bring about many-to many relationship . This relationship between the different data items . These are called as sets. In this we use a pointer to locate a particular record

The above diagram  describes the vendor and item relationship should be represents in Network model in this it describes  which vendor is selling a particular item.

Dr.E.F.CODD first introduced the relational database data model in 1970. this model allows  the data to be represented in a simple row and column format, table. A system which consist database in the form of tables is RDBMS.

      Each table indicating an entity , table consists rows and columns . Each column 

      indicates record or data of entity and each column indicates attribute or field.

Eg:

Vendor No	Vendor Name	Item
111	Ram	Mouse
121	Shyam	Keyboard
131	Arun	Monitor

Conceptual Data model or Objective based logical model: This model is consider with the represented in the database rather than how data is represented in an organization .It also included Entity Relationship model and uses this model in three types of relationships . These are

One-to-one Relationship: This type of relationship mainly has to represent the relationship between two set values and these set values have a relationship between one set to another set values  and specify the one-to-one relationship is shown as in the below. .Eg:

                  Set A               Set B

                  1          à        a

                  3          à        b

                  9          à        d         

One-to-many Relationship:  This type of relationship mainly has to represent the relationship between two set values and  the single value of one set should be participate in the relationship with another set of  two different values and form One-to-many relationship . In this way   the second set of more than one values should be  traced with single value of first set . Eg:

 

Many-to-Many Relationship: These types of relationship mainly have to represent the relationship between two set values and the value of the first set  should be participate in the relationship with more than single values of another set values and the same time  the value of second set should be traced with more than one value and form a Many-to-Many Relationship. Eg:

 

E-R Model (Entity-Relationship Model): Entity Relationship model consist of entities and specify the relationship among one or more than one entities and form a Entity Relationship Model. Overall logical structure of a DBMS can be expressed graphically by on E-R diagram which consist the following components. Eg:

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DATABASE ENVIRONMENT

Database Environment :

Introduction:

Database is used to store, manipulate and retrieve data in every type of organization like Business, Healthcare, Education, Govt and Libraries. Database technology is used by Individuals like Personal Computers, or by working groups Like Department wise, and Enterprise wise and Distributed wise.

Many organizations are today building separate database these databases are called data warehouses   . By using database we can develop relational database management, Online management System, and Employee Relationship management system. Etc.

By using database we can create or develop , retrieve and maintenance an organization data conveniently and successfully.

Data is a collection of raw facts . These facts may be in text, symbols, sounds, graphysics etc. data is the real thing of  database of an organization.

Eg. ABC group of institutions. Hyderabad.

Characteristics of DBMS:

DBMS is a mechanism to manage the designed database i.e. to create the data , insert the data, to update the data, and to delete the data in and from the database.

DBMS represents complex relationships between the data or information.

DBMS has a centralized data dictionary to store  metadata .

DBMS keeps data control and redundancy i.e. avoid duplicate data.

DBMS has automatic intelligent backup and recovery procedures for its units.

DBMS provide different user interfaces to manipulate the data in the database.

Data Independency is a process the separation of data description from metadata  i.e. in an organization data not depends on metadata. Each database should have database applications i.e. A large program  or set of programs to perform a specified action is a n application .In database by using application we can  read, write, update and delete of database information . An application which is used to perform database operations like read, write, update and delete is known as database application. When we develop our own database we should consider the legacy system or data. Legacy data means  any data which is installed before developing our own database in the system is known as Legacy data. It contained by the system which is used prior to the installation of the system. When we develop a personnel database we should follow the database constraint. Constraint means when we develop our own database we should follow certain rules and conditions these rules and conditions are known as constrains.