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Database is the long-term storage in the computer, is a collection of related information that is organized, shared data collection and so that can easily be accessed. Data in the database organized according to a certain data model, description and storage redundancy with a smaller, higher scalability and ease of data independence, and for a variety of users to share.
Database management system is a large database manipulation and management software is used to create, use and maintenance of databases, referred to as DBMS It unified database management and control to ensure the safety and integrity of the database. DBMS users to access data in the database, the database administrator to maintain the database through the DBMS work. It offers a variety of functions, enable multiple applications and users in different ways or at different times at the same time to create, modify, and ask the database.
Previously, database was found only in special research laboratories. Today database are a ubiquitous part of the information technology industry and business in general. A daily life as banking transaction, travel reservation, employment relationship, website searches, online and offline purchases are recorded in served by database. DBMS can manage any form of data including text, images, sound and video. Database and file structures are always determined by the software.
Figure 1-2 shows a sample flat file system, a subset of the data for fictional company Northwind Traders, a supplier of international food items (and a Microsoft sample database). Keep in mind that the column titles (Customer ID, Company Name, and so on) are included for illustration purposes only- only the data records would be stored in the actual files. Customer data is stored in a Customer file, with each record representing a Northwind customer. Each employee of Northwind has a record in the Employee file, and each product sold by Northwind has a record in the Product file. Order data (orders placed with Northwind by its customers) is stored in two other flat files. The Order file contains one record for each customer order with data about the orders, such as the customer ID of the customer who placed the order and the name of the employee who accepted the order from the customer. The Order Detail file contains one record for each line item on an order (an order can contain multiple line items, one for each product ordered), including data such as the unit price and quantity. An application program is a unit of computer program logic that performs a particular function within an application system. Northwind Traders has an application program that prints out a listing of all the orders. This application must correlate the data between the five files by reading an order and performing the following steps: 1. Use the customer ID to find the name of the customer in the Customer file. 2. Use the employee ID to find the name of the related employee in the Employee file. 3. Use the order ID to find the corresponding line items in the Order Detail file. 4. For each line item, use the product ID to find the corresponding product name in the Product file. This is rather complicated given that we are just trying to print a simple listing of all the orders, yet this is the best possible data design for a flat file system. One alternative design would be to combine all the information into a single data file with all the data about the customer, employee, and order combined into a single record for each order. Although this would greatly simplify data retrieval, consider the
A table is a logical group of columns. For example, may have a table that stores details of customer names and addresses. Another table would be used to store details of parts and yet another would be used for supplier names and addresses.
It is the tables that make up the entire database and it is important that do not duplicate data at all. Only keys would duplicate .Think of it as being like a rectangular spreadsheet made up of rows and columns.
Unlike a spreadsheet where the user is free to have different data on each row, in a database table, every row can only contain the types of data that were specified. Each column specifies the type of data stored (numbers, strings or binary data - such as images).
Columns are akin to fields, that is, individual items of data that we wish to store. A customer names, the price of a part, the date of an invoice are all examples of columns. They are also similar to the columns found in spreadsheets (the A, B, C etc along the top).
Rows are akin to records as they contain data of multiple columns (like the 1,2,3 etc in a spreadsheet). Unlike file records though, it is possible to extract only the columns you want to make up a row of data. Old "records" that computers read forced the computer to read EVERYTHING, even if you only wanted a tiny portion of the record. In databases, a row can be made up of as many or as few columns as you want. This makes reading data much more efficient - you fetch what you want.
Have a student table that included a record for each student at a College. The student unique student ID number would be a good choice for a primary key in the student table. The student first and last name would not be a good choice, as there is always the chance that more than one student might have the same name.
In a relational database, relationships enable you to prevent redundant data.
Once ready to start working with the data, you rely on relationships between the tables to pull the data together in meaningful ways. For instance, order information is useless unless you know which customer placed a particular order. However, you don't store customer and order information in the same table. Instead, you store order and customer data in two related tables and then use a relationship between the two tables to view each order and its corresponding customer information at the same time.
In a relational database, relationships enable to prevent redundant data. For example, the designing a database that will track information about book, might have a table called Title that stores information about each book, such as the book title, date of publication, and publisher. There is also information might want to store about the publisher, such as the publisher address, code, and phone number. If to store all of this information in the titles table, the publisher phone number would be duplicated for each title that the publisher prints.
A better solution is to store the publisher information only once in a separate table, Publishers. You would then put a pointer in the Titles table that references an entry in the Publishers table.
To make sure that your data is not out of sync, you can enforce referential integrity between the Titles and Publishers tables. Referential integrity relationships help ensure that information in one table matches information in another. For example, each title in the Titles table must be associated with a specific publisher in the Publishers table. A title cannot be added to the database for a publisher that does not exist in the database.