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A database is a collection of related data from which is users can efficiently retrieve the desired information.it can be anything from a simple collection of roll numbers ,names addresses and phone numbers of students to a complex maze of interrelated facts and text .
Data redundancy :Redundancy implies duplication ( or repetition) of the same data in different files .For example in the traditional record keeping system ,the administration department of a school maintains the contact details including the addresses of the students in a file in addition their addresses are stored with the result in a separate file .This leads to redundant storage of the address.The database management systems ,on the other hand maintain all the data in a single repository ( Centralised location ) .
Data inconsistency : When there are two files containing the same data and one file is updated while the other files contains the old data,it leads to inconsistency of data.For example ,the address of a student is changed.The required change is made in the records maintained by the administration department but not in the file storing the results,now,there exist two different addresses of the same student in two different files,which lead to inconsistent data.By storing the data in a single place ,database management systems avoid data inconsistency.
3. What is DBMS and RDBMS?
A Database Management System (DBMS) is a software package that facilitates that the creation,maintenance and use of a computerised database.Some of the commonly used DBMS are Microsoft Access ,Oracle,DB2 and FoxPro .
The DBMS design based on a relational database model is known as the Relational database Management System (RDBMS) .
A primary key is a field that has a unique value for all records in the table.A primary key value cannot be NULL ,which implies that a field which is a primary key,must have some data
1. Open the table in the Design view.
2. Select the field Roll Number.To select ,press Shift + Spacebar or click the area to the left of the field name when the mouse pointer changes to an arrow.
3. Click the Edit menu and then click Primary Key,or right click the selected field and click Primary Key on the shortcut menu that appears.This displays a key symbol 
adjacent to the field name .
Text
It is the default data type and can contain any combination of letters , numbers ,special characters ( like @,! and %) and spaces.This data type can have up to 255 characters .
Currency
It is similar to the Number data type and can be used in calculations.This data type automatically displays a dollar sign and thousand separators (commas) .Negative numbers are displayed in parentheses .Note that this field is widely used as it is faster in calculations than the number data type.
Date / Time
It is used to specify the date and time in a table.Note that only the valid dates and times are allowed .For example ,if you enter 31 st April,Microsoft Access displays a message of invalid date.This data type is used to perform calculations based on dates and times .
Lookup Wizard
It creates a list of selected values from the table or a list of values provided by the user .This field saves the data entry time in the table .
It automatically generates a number ( starting from 1) and assigns it to each record in the database.Note that you cannot manually enter a value into this type of field or change the number once Access assigns it. This data type can be used when you want a unique identification number for every record .
An input mask is the format we will assign for the introduction of values into a field.This property specifies a particular pattern while entering the data in the field.For this ,it uses different characters like '-' or '/'.Input Mask is applicable to the Text,Number,Currency and Date/Time data types.
| Special characters | Description |
| 0 | represent a required digit from 0 to 9 -no '+' or '-' sign is allowed |
| 9 |
represent an optional digit or space-no '+' or '-' sign is allowed |
| # | represent an optional digit -'+' or '-' sign allowed |
| L | represent a required letter from A to Z |
| ? | represent an optional letter from A to Z or space |
| A | represent a required letter or digit |
| a | represent an optional digit or letter |
| & | represent any character or space |
| C | represent an optional character or space |
| > | forces the following characters to be converted to uppercase |
| < | forces the following characters to be converted to lowercase |
| ! | causes the following characters to be displayed right to left rather than left to right |
| / | represents that the text next character to be displayed is a constant |
| Password | creates a text box for the password and displays any character typed in the text box as a '*' symbol |
♦ Validation Rule
A validation rule limits or controls what users can enter in a table field or a control (such as a text box) on a form. This property defines a 'check'(validation) before entering the data in the table.This process of setting a limit while entering data is known as data validation. It enables the user to enter data according to the specified checks.Validation Rule can be set in the database according to the requirement.
♦ Validation Text
This property specifies the message that is to be displayed when the data entered violates the given condition in Validation Rule.The text entered in this property is displayed as a message.
Data inconsistency exists when different and conflicting versions of the same data appear in different places. Data inconsistency creates unreliable information, because it will be difficult to determine which version of the information is correct.
Data inconsistency is likely to occur when there is data redundancy. Data redundancy occurs when the data file/database file contains redundant - unnecessarily duplicated - data. That's why one major goal of good database design is to eliminate data redundancy.
A database management system (DBMS) is a system that allows to build and maintain databases, as well as to utilize their data and retrieve information from it. A DBMS defines the database type that it supports, as well as its functionality and operational capabilities. A DBMS provides the internal processes for external applications built on them. The end-users of some such specific application are usually exposed only to that application and do not directly interact with the DBMS. Thus end-users enjoy the effects of the underlying DBMS, but its internals are completely invisible to end-users. Database designers and database administrators interact with the DBMS through dedicated interfaces to build and maintain the applications' databases, and thus need some more knowledge and understanding about how DBMSs operate and the DBMSs' external interfaces and tuning parameters.
DBMS architecture specifies its components (including descriptions of their functions) and their interfaces. DBMS architecture is distinct from database architecture. The following are major DBMS components:
DBMS external interfaces - They are the means to communicate with the DBMS (both ways, to and from the DBMS) to perform all the operations needed for the DBMS. These can be operations on a database, or operations to operate and manage the DBMS. For example:
An external interface can be either a user interface (example., typically for a database administrator), or an application programming interface (API) used for communication between an application program and the DBMS.
Data inconsistency exists when different and conflicting versions of the same data appear in different places. Data inconsistency creates unreliable information, because it will be difficult to determine which version of the information is correct.
Data inconsistency is likely to occur when there is data redundancy. Data redundancy occurs when the data file/database file contains redundant - unnecessarily duplicated - data. That's why one major goal of good database design is to eliminate data redundancy.
Each application that requires files for processing maintains a separate copy of the files.this leads to data redundancy.
Extensive programming is required .That is ,separate programs or modules have to be written for different operations to be performed on various files.
Making changes in a file implies changes in the application program,which is a difficult and time consuming task.In other words ,application programs are depended on the data.
A system get more complex managing files gets more difficult
The security features are difficult to handle.
The DBMS includes various features that overcome the short comings of traditional file system and make DBMS a powerful tool to design and create database.These features are listed :
Easy to learn : Most of the database management systems are easy to learn and use.No specialised training is required to work on a DBMS.
Reduce data redundancy : Most of the database management system are designed to reduce data redundancy.Redundancy implies duplication of the same data in different files.
Reduce data inconsistency : Most of the database management system are designed to avoid data inconsistency which is a result of data redundancy.
Facilitated data sharing : Most of the database management system allow sharing of data among multiple users and applications.For this,the data is created or stored in one repository and can be made available to different users according to their requirements.
Enforces data standards : Most database management systems ensure that the data stored is in a standard format.Standardizing helps in sharing data among different users.
Password protected : Most of the database management system allow users to provide a password to their database which provides security to the data from unauthorised access.
Extensive help : Most of the database management systems include an extensive built-in-help feature.This feature can be used whenever a user faces some problems while using any database management application.
The database model describes the way in which the database is structured in the database management system.The objectives of database model is to organise the data logically and physically.
The various database models are :
Hierarchical model : In this model ,the data is arranged in a hierarchical structure which describe the relationship of the record of the table in a 'tree -like' or 'parent -child' structure.In this model ,the records are represented as nodes.They are linked with other superior records on which they are dependent and also on the records which are depended on them.
Network model : In this model,the data is represented by establishing a relationship between the records.This model is an improvement over the hierarchical database model.The records in this model can be linked with many records.
Relational model :In this model ,the data is organised in the form of rows and columns to from a table and the table can be related to each other for sharing the data.The relational model is the most powerful database models since its design is easier as compared to other database models.
i.Tables
Components of a table
Practice in Related Chapters |
| Microsoft Access |
| Internet |
| Services Available on Internet |
| Web Browser |
| Hypertext Markup Language |
| Societal Impact of IT |
| Extensible Markup Language |
