View:

- Tail raid data representation is provided by a view to access data from its table.

- It has logical structure can not occupy space.

- Changes get affected in corresponding tables.

Materialized view

- Pre calculated data persists in materialized view.

- It has physical data space occupation.

- Changes will not get affected in corresponding tables.

Star schema: A highly de-normalized technique. A star schema has one fact table and is associated with numerous dimensions table and depicts a star.

Snow flake schema: The normalized principles applied star schema is known as Snow flake schema. Every dimension table is associated with sub dimension table.

Differences:

- A dimension table will not have parent table in star schema, whereas snow flake schemas have one or more parent tables.

- The dimensional table itself consists of hierarchies of dimensions in star schema, where as hierarchies are split into different tables in snow flake schema. The drilling down data from top most hierarchies to the lowermost hierarchies can be done.

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.

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.

Opendir():- It opens the directory. This function returns a directory stream on success and FALSE and an error on failure.

Syntax:

Opendir(directory, context)

Context is a set of options that can modify the behavior of a stream

Example: opens sample directory.

$dir = opendir("directory");

Readdir(): It returns an entry from a directory handle opened by opendir().

Syntax:

Readdir(dir_stream)

Example:

$file = readdir($dir);

closedir(): It closes a directory handle opened by opendir().

Syntax:

closedir(dir_stream)

Example:

$file = close($dir);