Zope is a framework that allows developers of varying skill levels to build web applications . You will learn Zope's purpose and audience in greater detail, and what makes Zope different from similar applications.

Free Ebook on Web Application: The Zope Book (2.6 Edition).pdf

What Is A Web Application?

It is often important that visitors to a website see content that is timely and up-to-date. A time-dependent site's content needs to change continually. For example, if a commercial website helps its visitors sell and buy used automobiles, it is usually required that the site run advertisements only for cars that have not yet been sold. It is also important that new ads be posted at most a day or two after they've been placed by a seller. If either of these requirements is not met, the website will likely not be very successful.

The layout of text and images that show up in a user's web browser when the user visits a website are often composed using a simple language known as Hyper Text Markup Language (HTML). When a user visits a typical website, a chunk of text that is "marked-up" with HTML is transferred between the website and the user's browser. The browser interprets the chunk of text, showing text and images to the user. The chunk of text which is transferred is typically referred to as a page . Many website visitors think about navigation in terms of moving "from page-to-page" within a website. When they click on a hyperlink, their browser transports them to a new page. When they hit their browser's Back button, it takes them to the last page they've visited.

Some websites are static . Static websites require a person with a privileged level of access (sometimes termed the webmaster ) to manually "freshen" the site's content. Freshening the content requires the person to manually visit and update the HTML that makes up each page that needs to change. Typically, this is done by editing a set of files on the web server (the machine that runs the website), where each file represents a single page........more

Site-wide changes to the "look-and-feel" of a static website require that the webmaster visit and update each and every file that comprises the website. Websites can typically grow to encompass thousands of files, so this can become a non-trivial task. The webmaster responsible for our automobile advertising website has the additional responsibility of keeping the ads themselves fresh. If each page in the website represents an ad for a particular automobile, he needs to delete the pages representing ads which have expired and create new pages for ads which have been recently sold. He then needs to make sure that no hyperlinks on other pages point to missing pages.

This becomes a lot of work very quickly. As you can imagine, with any more than a few pages to update every day, this can become pretty dull. The webmaster also understandably makes mistakes (he's human, after all), and forgets to update or remove critical pages.

Somewhere down the line smart webmasters begin to think to themselves, "Wow, this is a lot of work. It's tedious and complicated, and I seem to be making a lot of mistakes. Computers are really good at doing tedious and complicated tasks, and they don't make very many mistakes. I bet my webserver computer can automatically do a lot of the work I now do manually." At this point, the webmaster is ready to be introduced to web applications .

A web application is a computer program that users invoke by using a web browser to contact a web server via the Internet. Users and browsers are typically unaware of the difference between contacting a web server which fronts for a statically-built website and a web server which fronts for a web application. But unlike a static website, a web application creates its "pages" dynamically . A website that is dynamically-constructed uses an a computer program to provide the dynamism. These kinds of dynamic capplications can be written in any number of computer languages. In a dynamically-constructed website, the webmaster is not required to visit the site "page-by-page" in order to update content or style. Instead, he is able to create a "common look and feel" for the set of pages that make up his website. He is also able to instruct the webserver to generate an HTML page on the fly that includes certain unique bits of content. If our auto-classified-ad webmaster chose to construct a web application to maintain his classifieds system, he could maintain a list of "current" ads separate from the HTML layout (perhaps stored in a database of some kind). He could then instruct his web application to query this database and generate a particular chunk of HTML that represented an ad or an index of ads when a user visited a page in his website.

Web applications are everywhere. Common examples of web applications are those that let you search the web, like Google ; collaborate on projects, like SourceForge ; buy items at an auction like eBay ; communicate with other people over e-mail, like Hotmail ; or view the latest news ala CNN.com .

A framework which allows people to construct a web application is often called a web application server , or sometimes just an application server . Zope is a web application server, as are competing products like BEA WebLogic , Macromedia ColdFusion and (to some extent) Vignette StoryServer . A web application server typically allows a developer to create a web application using some common computer programming language. But it also provides services beyond the basic capabilities of the language such as templating, a common security model, data persistence, sessions, and other features that people find useful when constructing a typical web application

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