A data island is a store of hidden data in a web page and is accessible through an extensible markup language (XML) file. Data islands can be useful for making information available when necessary without bogging down the contents of a web page with large amounts of data that might create slow load times. This method of hiding information on a web page is not usable with all browsers, however, which is something that users should consider.
In a data island, the user creates a reference to an XML file and embeds it in the page. If there is a situation when data from that file needs to be displayed, the dynamic page can serve up that content. For instance, on an e-commerce site, the contents of the shopping cart might be encoded in XML. The user can hover to see a list of the things that he or she has in his cart, but this information remains hidden the rest of the time.
Coding tricks such as using data islands can make overall files much smaller. This can be important for Internet users on slow connections who have difficulty loading resource-rich pages. The flexibility of data islands also can be useful for reducing loads on the server. If the user doesn't need the data, it doesn't display, and this limits calls to the server. When the user does have a need to access it, it can quickly be brought up through the XML file.
The issue with data islands is browser compatibility, an ongoing problem across the Internet. Each browser displays and handles information slightly differently. This might cause minor problems, such as when a web page does not display quite the right color. It also can be a significant issue when it involves code that will not display at all or will return errors when the browser attempts to display it. The data island does not work and perform reliably across all browsers, and designers might consider other, more standardized, methods for hiding information until users actually need it.
This term is also used in reference to external storage devices with high capacity but limited connectivity. Users can interact with the data island to play music, read books and watch movies. If they want to get material on or off, they will need to specifically connect the data island to another computer to synchronize it and transfer the data.