Introduction to database:


A database is the collection of related information. In other words, database is collection of data organized in a manner that allows easy access, retrieval and use of that data.
In a manual database, you might record data on a paper and store it in filling cabinet. Database software, like access, is software that allows you to create access and manage a database.
Using database software, you can add, change and delete data in the database retrieve data from the database; and create forms and reports using the data in the database. Phone book is an example of database. The phone book contains several items of information like name, address, phone number, etc., of each phone subscriber in a particular area. In the database, each subscriber’s information will be saved in the same format.
In the term of database, the phone book is a table which contains a record of each subscriber. Each subscriber record contains three fields: name, address, and phone number. The records are sorted alphabetically by the name field, which is called the key field.

Components of a database:

In a database, data is stored in a database file. Data may be arranged in tables related to one another.

FIELD
:
Field is a single column or a unit in a table with unique name.

RECORDS
:
A record is a group of related fields. For example, a student record includes a set of fields about one student.

TABLE
:
Tables are the places where all the information in your database is stored in the form of rows (records) and columns (fields).

DATABASE
:
By default, each table appears as a spreadsheet grid called a database. You can type directly into a database.

FORM
:
Forms are like dialogue boxes that prompt for field entries and used to make data entry more convenient. An attractively formatted form is easier and more pleasant to use to enter new records than a plain datasheet.

FILTERS
:
It is often useful to display a filtered view of a table. You can filter a table to show only certain records, only certain fields, or both.

QUERIES
:
You can create a query, which is like a saved filter. Queries also enable you to combine data from multiple related tables into a single datasheet of results.

REPORTS
:
Reports present data from tables and queries in an attractive, customization format complete with titles, headers and footers, and even logos and graphics.

Database organization:

Before you begin creating a database, you should perform some preliminary tasks. Make a list of the data items you want to organize; each of these will become a field in the database.

Field
:
A field is a combination of one or more related characters or bytes and is the smallest unit of data a user accesses. A field name uniquely identifies each filed. When searching for data in a database, you often specify the field name. Field names for the data in the student file are Student ID, First Name, Last Name, Class, Fees. A database uses a variety of characteristics, such as field size and data type, to define each field.

Field
size:
The field size defines the maximum number of characters a field can contain. For example, the Student ID field contains 6 characters and thus has a field size of 6.

Field
type:
Each field has a data type that defines what you can store in it. Data entry is restricted to valid entries for the type you choose, which helps to prevent data-entry errors. For example, you cannot enter letters in a field set to number, and you must enter valid dates or times in a Data/Time field.

Text
:
This is a general-purpose field containing any data. It has a limit of 255 characters and cannot be used for numeric calculation. Use this type for numeric entries that will not have calculations performed on them, such as telephone numbers and ZIP codes.

Memo
:
This type has a limit of 63,999 characters; used for detailed, descriptive fields.

Numbers
:
This type stores numeric data that you can use in calculations. It can also hold symbols, such as decimal points and commas.

Date/Time
:
This type only stores numbers representing valid dates and times.

Currency
:
Stores currency data that you can use in calculations.

Auto
Number:
Stores a sequential number for each record.

Yes
/No:
The value 1 represents yes, and the value 0 represents No, but the field can be formatted to display values as True/False, On/Off, or Yes/No.

OLE
Object:
Stores objects created in another application, such as Word or Excel that you can link or fill in an Access table.

Hyperlink
:
You can link to Websites, e-mail addresses, files on your computer, files on a LAN, or virtually any other location.

Lookup
Wizard:
Depending on the usage, this type creates either a lookup list from data that you specify or lookup list from the values in another table. It can also be used to set up multi-valued lists.

Attachment
:
This type works only in Access 2007 and Access 2010 databases. You can attach data files from word processing programs, spreadsheets, and graphics editing programs, and so on.

Calculated
:
This field type is new in Access 2010. You can use it to create calculated fields directly in a table; in earlier versions, you could create calculated fields in queries.

Entering data:

After a table structure is created, you can enter individual records into a table. Records usually are entered one at a time using that keyboard, often through a data entry form. As you are entering the data, the database software checks, or validates, the data. Validation is the process of comparing the data to a set of defined rules or values to determine if the data is acceptable. For example, designating a field as a numeric data type allows a user to enter only numbers into the field. Validation is important because it helps to ensure that data entered into the database is error-free. Another way to enter data into a database is to import data from an existing file. For example, you can import data saved in a spreadsheet file into a database.

Manipulating data:

Once the records are entered, you can use the database software to manipulate the data to generate information. For example, you can sort or organize a set of records in a particular order, such as alphabetical or by entry date. You can also retrieve information from the database by running a query. A query is a specific set of instructions for retrieving data from the database.

RDBMS-RELATIONAL DATABASE MANAGEMENT SYSTEM

A DBMS (Database Management System) that is based on relational model is known as RDBMS (Relational Database Management System). RDBMS provides a comprehensive and integrated approach to information management. A relational model provides a basis for a relational database. A relational model has three aspects:

1. Structure:
It consists of a collection of objects or relations that stores data. An example of relation is a table. You can store information in a table and use the table to retrieve and modify data.

2.Operations:
These are used to manipulate data and structures in a database. When using operations, you must adhere to a predefined set of integrity rules.

3.
Integrity Rule:
These are laws that govern the operations allowed on data in a database. This ensures data accuracy and consistency.





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