OLTP stands for OnLine Transaction Processing. Applications that supports and manges transactions which involve high volumes of data are supported by OLTP system. OLTP is based on client-server architecture and supports transactions across networks.

OLAP stands for OnLine Analytical Processing. Business data analysis and complex calculations on low volumes of data are performed by OLAP. An insight of data coming from various resources can be gained by a user with the support of OLAP.

Business facts or measures and foreign keys are persisted in fact tables which are referred as candidate keys in dimension tables. Additive values are usually provided by the fact tables which acts as independent variables by which dimensional attributes are analyzed.

Attributes that are used to constrain and group data for performing data warehousing queries are persisted in the dimension tables.

Data mining is a method for comparing large amounts of data for the purpose of finding patterns. Data mining is normally used for models and forecasting. Data mining is the process of correlations, patterns by shifting through large data repositories using pattern recognition techniques.

Data warehousing is the central repository for the data of several business systems in an enterprise. Data from various resources extracted and organized in the data warehouse selectively for analysis and accessibility.

Data warehousing is a process of repository of electronic data of an organization. For the purpose of reporting and analysis, data warehousing is used. The essence concept of data warehousing is to provide data flow of architectural model from operational system to decision support environments. 

Notify URL and Return URL is used in Paypal Payment Gateway integration. Notify URL is used by PayPal to post information about the transaction. Return URL is used by the browser; A url where the user needs to be redirected on completion of the payment process.

The function unlink() is to remove a file, where as unset() is used for destroying a variable that was declared earlier.

Htmlentities() converts all applicable characters to HTML entities. While htmlspecialcharacter()converts special characters to HTML entities. This means htmlentities( ) will check for non English language characters, such as French accents, the German umlaut, etc.

Copy() makes a copy of the file. It returns TRUE on success. It can copy from any source to destination. Move simply Moves the file to destination if the file is valid. While move can move the uploaded file from temp server location to any destination on the server. If filename is a valid upload file, but cannot be moved for some reason, no action will occur.