DATA ORGANIZATION 

The first step in understanding databases is to learn how data is organized. In the logical view, data is organized into groups or categories. Each group is more complex than the one before.

 

• Character: A character is the most basic logical data element. It is a single letter, number, or special character, such as a punctuation mark, or a symbol, such as $.

 • Field: The next higher level is a field or group of related characters. In our example, Masurkar is in the data field for the Last Name of an employee. It consists of the individual letters (characters) that make up the last name. A data field represents an attribute (description or characteristic) of some entity (person, place, thing, or object). For example, an employee is an entity with many attributes, including his or her last name.

 • Record: A record is a collection of related fields. A record represents a collection of attributes that describe an entity. In our example, the payroll record for an employee consists of the data fields describing the attributes for one employee. These attributes are First Name, Last Name, Employee ID, and Salary.

• Table: A table is a collection of related records. For example, the Payroll Table would include payroll information (records) for the employees (entities). 

• Database: A database is an integrated collection of logically related tables. For example, the Personnel Database would include all related employee tables including the Payroll Table and the Benefits Table.

KEY FIELD 

Each record in a table has at least one distinctive field , called the key field . Also known as the primary key , this field uniquely identifies the record . Tables can be related or connected to other tables by common key fields .

 
For most employee databases , a key field is an employee identification number . Key fields in different tables can be used to integrate the data in a database . For example , in the Personnel Database , both the Payroll and the Benefits tables include the field Employee ID . Data from the two tables could be related by combining all records with the same key field ( Employee ID ) .

BATCH VERSUS REAL-TIME PROCESSING

 Traditionally, data is processed in one of two ways. These are batch processing, or what we might call "later," and real-time processing, or what we might call "now." These two methods have been used to handle common record-keeping activities such as payroll and sales orders. 

• Batch processing:

 In batch processing, data is collected over several hours, days, or even weeks. It is then processed all at once as a "batch." If you have a credit card, your bill probably reflects batch processing. That is, during the month, you buy things and charge them to your credit card. Each time you charge something, an electronic copy of the transaction is sent to the credit card company. At some point in the month, the company's data processing department puts all those transactions (and those of many other customers) together and processes them at one time. The company then sends you a single bill totaling the amount you owe.

• Real - time processing :

 Real- time processing , also known as online processing , occurs when data is processed at the same time the transaction occurs . For example , whenever you request funds at an ATM , real - time processing occurs . After you have provided account information and requested a specific withdrawal , the bank's computer verifies that you have sufficient funds in your account . If you do , then the funds are dispensed to you , and the bank immediately updates the balance of your account .