* A group of bits, called a byte, represents a single character, which can be a letter, a number, or another symbol.
* A grouping of characters into a word, a group of words, or a complete number (such as a person’s name or age) is called a field.
* A group of related fields, such as the student’s name, the course taken, the date, and the grade, comprises a record.
* A group of records of the same type is called a file.
* A group of related files makes up a database.
* A record describes an entity.
* An entity is a person, place, thing, or event on which we maintain information.
* An order is a typical entity in a sales order file, which maintains information on a firm’s sales orders.
* Each characteristic or quality describing a particular entity is called an attribute. * For example, order number, order date, order amount, item number, and item quantity would each be an attribute of the entity order.
* Every record in a file should contain at least one field that uniquely identifies instances of that record so that the record can be retrieved, updated, or sorted.
* This identifier field is called a key field
r, which can be a letter, a number, or another symbol.
The Data Hierarchy
Entities and Attributesing ers into a word, a group of words, or a complete number (such as a person’s name or age) is called a field. Levels of Abstraction
* Physical level: describes how a record (e.g., customer) is stored. * Logical level: describes data stored in database, and the relationships among the data.
type customer = record
customer_id : string;
customer_name : string;
customer_street : string;
customer_city : string;
* View level: application programs hide details of data types. Views can also hide information (such as an employee’s salary) for security purposes.
View of Datahe other hand a group of bits called a byte represents a single character which can be a letter, a number or another symbol. A grouping of character into a word, a group of words or a complete number is called field. A group of related fields comprises a record; a group of records of the same type is called a file. A group of related files ma
DATA BASE MANAGEMENT SYSTEM Meaning of Data base-
A database is an organized collection of facts. In other words it is collection of information arranged and presented to serve an assigned purpose. An example of data base is a dictionary, where words are arranged alphabetically. Another example is a telephone directory, where subscriber names are listed in an alphabetical order. Similarly a box of cards with names and addresses written as mailing list, then the box and its contents form a mailing database. The collection of these cards will be termed as database. In order to keep database updated we may need to perform the operations like adding, removing, editing information, etc. In case of telephone diary where we note down the names, address, and phone numbers of our friends. This is also a type of database. When we make our new friends and add the information about them in our diary, it is equivalent to the adding data to the database. If address of our friend changes and we note new address in our diary, it is editing a database. If we want to send a letter to our friend then we look into...