Question

Fill in the blanks in each of the following statements: a. The two most common HTTP request types are ___ and ___. b. Browsers often \(\quad\) Web pages for quick reloading. c. In a three-tier application, a Web server is typically part of the ___ tier. d. In the URL http://www. deitel.com/books/downloads.html. www. deitel.com is the ___ of the server, where a client can find the desired resource. e. \(A(n) \quad\) document is a text file containing markings that describe to a Web browser how to display and format the information in the document. f. The environment variable \(\quad\) provides a mechanism for supplying data to CGI scripts. g. \(A\) common way of reading input from the user is to implement the XHTML \(\quad\) element.

Short answer

a. GET, POST; b. cache; c. middle; d. host; e. hypertext; f. QUERY_STRING; g. form.

Step-by-step solution

Identifying HTTP Request Types

The two most common HTTP request types are GET and POST. GET requests are used to retrieve data from a server, whereas POST requests are used to send data to a server.

Understanding Web Page Caching

Browsers often cache Web pages for quick reloading. Caching allows browsers to store copies of web pages so they can be quickly accessed without reloading them from the server.

Identifying Tiers in a Three-Tier Application

In a three-tier application, a Web server is typically part of the middle tier. The three tiers usually consist of a client tier, a middle tier (web server), and a data tier (database server).

Understanding URL Components

In the URL http://www.deitel.com/books/downloads.html, www.deitel.com is the host of the server, where a client can find the desired resource. The host specifies the server address recognized by the domain name system.

Describing Web Documents

A hypertext document is a text file containing markings (commonly HTML) that describe to a Web browser how to display and format the information in the document.

Explaining Environment Variables for CGI

The environment variable QUERY_STRING provides a mechanism for supplying data to CGI scripts, typically as part of a URL.

Reading User Input with XHTML

A common way of reading input from the user is to implement the XHTML form element. Forms can include various types of input fields, such as text boxes, checkboxes, and radio buttons, for user interaction.

Key concepts

HTTP Request Types

In the realm of web development, understanding HTTP request types is essential. HTTP, or Hypertext Transfer Protocol, is the foundation of data communication on the World Wide Web. Two of the most commonly used HTTP request types are **GET** and **POST**.

• **GET Requests:** These are used primarily to retrieve data from a server. When a web browser loads a page, it often uses a GET request to fetch the HTML document from the web server. GET requests are considered safe and can be bookmarked or cached.
• **POST Requests:** Conversely, POST requests are used to send data to a server, often used in form submissions. The data sent will not be visible in the URL and is not cached, making POST more suitable for sensitive or large amounts of data.

Both GET and POST are integral to building interactive and dynamic web applications, each serving distinct purposes in data handling.

Web Page Caching

Web page caching is a technique that increases the speed at which users can access a previously visited web page. Browsers store copies of web pages locally, known as the cache, which allows for faster reloading without having to fetch the data again from the server.

• **Benefits of Caching:** Reduces server load and bandwidth usage, improves page load times, and enhances user experience by providing quicker access to frequent content.
• **Types of Caching:** Includes browser caching, where the browser caches web pages, and server caching, where the server stores copies of web resources after initially sending them to the client.

Effective caching strategies can greatly enhance the performance of web applications, especially for resource-heavy or frequently accessed sites.

Three-Tier Application

A three-tier application architecture divides applications into three detached layers, each with specific responsibilities. This architecture provides scalability, manageability, and flexibility in web development.

• **Client Tier:** This is the front-end user interface, typically interacted with via web browsers.
• **Middle Tier (Web Server):** Acts as an intermediary, processing client requests and retrieving data from the database server. This tier is often where business logic is executed.
• **Data Tier (Database Server):** The backend layer, responsible for storing data and managing data retrieval. It houses the application's data and database management systems.

By separating these components, developers can maintain and scale each tier independently, making three-tier applications robust and efficient.

URL Components

A URL (Uniform Resource Locator) is like a web address, used to locate resources on the Internet. Understanding the components of a URL is vital in web development.

• **Protocol:** Such as http or https, indicates the method used to access the resource.
• **Host:** This is the server's address, for example, *www.deitel.com* in the URL example. The host identifies the domain name, where users can find the resource.
• **Path:** Directs to a specific resource on the server, like */books/downloads.html*. The path helps navigate through the directories within a site.

Each part of the URL plays a crucial role in guiding web browsers to retrieve the exact files required across the vast digital landscape.

HTML Documents

HTML, or Hypertext Markup Language, is the backbone of any web page's content structure. It provides the links between documents and is responsible for organizing the text and multimedia content displayed by browsers.

• **Markup:** HTML uses tags to structure a web page, telling the browser how elements like headings, paragraphs, images, and links should appear.
• **Formatting:** These tags add semantic meaning to web content, enhancing accessibility and user experience.
• **Cross-platform compatibility:** HTML documents are universally compatible, ensuring web pages can be displayed consistently across various devices and browsers.

Understanding HTML is foundational for anyone seeking to dive into the world of web design and development.

CGI Environment Variables

When dealing with web servers, CGI, or Common Gateway Interface, environment variables play a significant role in handling data exchange between web servers and cgi scripts.

• **QUERY_STRING:** One of the most important environment variables, it holds data included in a URL after the question mark (?), often used to pass parameters to CGI scripts.
• **HTTP_HOST and REQUEST_METHOD:** Other examples of CGI environment variables, providing details about host information and request type respectively.
• **Use in Web Development:** These variables enable servers to communicate dynamically with external scripts, playing a crucial role in the functionality of interactive web pages.

Understanding CGI environment variables allows developers to create more interactive and dynamic web applications, catering to specific user requests.

XHTML Form Element

Forms are essential for user interaction on websites, and XHTML (Extensible Hypertext Markup Language) forms take it a step further by offering more strict syntax rules than traditional HTML while maintaining compatibility.

• **User Input:** XHTML forms allow various types of user inputs, like text fields, checkboxes, and radio buttons, enhancing interaction.
• **Data Handling:** Once submitted, the form's data is sent to a server for processing, often leading to dynamic responses.
• **Enhanced Markup Standards:** XHTML aims to make code cleaner and more machine-readable, adhering to XML standards which increase robustness.

Mastering XHTML forms is key for developers aiming to collect user inputs efficiently, ensuring their web applications are both robust and user-friendly.