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A Web cache (or HTTP cache) is a system for optimizing the World Wide Web. It is implemented both client-side and server-side. The caching of multimedia and other files can result in less overall delay when browsing the Web. A forward cache is a cache outside the web server's network, e.g. in the client's web browser, in an ISP, or within a corporate network. A network-aware forward cache only caches heavily accessed items. A proxy server sitting between the client and web server can evaluate HTTP headers and choose whether to store web content. A reverse cache sits in front of one or more web servers, accelerating requests from the Internet and reducing peak server load. This is usually a content delivery network (CDN) that retains copies of web content at various points throughout a network. The Hypertext Transfer Protocol (HTTP) defines three basic mechanisms for controlling caches: freshness, validation, and invalidation.
This is specified in the header of HTTP response messages from the server. Freshness allows a response to be used without re-checking it on the origin server, and can be controlled by both the server and the client. For example, the Expires response header gives a date when the document becomes stale, and the Cache-Control: max-age directive tells the cache how many seconds the response is fresh for. Validation can be used to check whether a cached response is still good after it becomes stale. For example, if the response has a Last-Modified header, a cache can make a conditional request using the If-Modified-Since header to see if it has changed. The ETag (entity tag) mechanism also allows for both strong and weak validation. Invalidation is usually a side effect of another request that passes through the cache. For example, if a URL associated with a cached response subsequently gets a POST, PUT or DELETE request, the cached response will be invalidated. Many CDNs and manufacturers of network equipment have replaced this standard HTTP cache control with dynamic caching. In 1998, the DMCA added rules to the United States Code (17 U.S.C. ยง: 512) that exempts system operators from copyright liability for the purposes of caching. This is a list of server-side web caching software. Fountis, Yorgos (4 May 2017). "How does the browser cache work?". Messaoud, S.; Youssef, H. (2009). "An analytical model for the performance evaluation of stack-based Web cache replacement algorithms". International Journal of Communication Systems. Shinder, Thomas (2 September 2008). "Understanding Web Caching Concepts for the ISA Firewall". ISA Server. TechGenix Ltd. Erman, Jeffrey; Gerber, Alexandre; Hajiaghayi, Mohammad T.; Pei, Dan; Spatscheck, Oliver (2008). "Network-Aware Forward Caching" (PDF). Kelly, Mike; Hausenblas, Michael.
Have you ever wanted to try out a new personality? Since we're stuck with ourselves, day-in and day-out, our own personalities might sometimes feel a little tired from time to time. So what can we do about this? There are, of course, costumes, which are probably the reason so many people look forward to Halloween -- they can be their favorite superhero for a night and revel in a little creativity. But not all of us are willing to play dress up throughout the calendar year, mainly because doing so violates generally held social norms. After all, most Web sites that offer some kind of online community allow their users to create avatars, an electronic image that represents the person controlling it. Generally, members can be as creative as they like with their avatar, either fashioning it as close to their appearance and personality as possible or creating an entirely different personality.
One of these social networking services is Zwinky, a service launched in 2006 and owned by InterActiveCorp (IAC). Zwinky lets its members create their own cartoonish, large-headed and big-eyed avatars, which they can use in several different ways. One thing to keep in mind: Zwinky is open to anyone age 13 and older. If you're younger than 13, you won't be allowed to make your own account, not even with parental permission. Zwinky profiles can also be set to "private" if you're 18 or older, but profiles of Zwinky users younger than 18 are automatically set to private. So how does Zwinky work? What can someone with a Zwinky avatar do? And what kind of place is Zwinktopia, anyway? This may be a slightly unfamiliar approach for members of other social networking sites -- most simply request that you create a username and password and fill in some personal information, including e-mail addresses and phone numbers.
Zwinky, however, requires you to download a Zwinky icon onto your Web browser, which users click on to access the program's interface. When you've successfully installed the Zwinky program and opened up the program window, it's time to customize your Zwinky character. Every Zwinky has a personal wardrobe, which users can access by clicking on the "Open Wardrobe" button near the bottom of the screen. You can manipulate a Zwinky's appearance to make it look however you want, and users choose traits including gender, skin tone, hair style and color, and more. To move a Zwinky from one place to the next in a specific area, members simply use the mouse to point and click. You can make new friends or see a list of the ones you already have by clicking on the "View/Add Friends" button at the bottom of the interface. This button allows you to either send an e-mail to a fellow Zwinky requesting friendship or to see where in Zwinky's world your friends are.
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