Online service UIs have generally lacked about ten years behind computer UIs due to lack of bandwidth and a lowest-common-denominator approach. For example, window-based direct manipulation interfaces were introduced on mass-market personal computers in 1984, but the same class of user experience has not been offered in major online services until 1995.
First Generation: No-Interaction Online Services
Early online services did not offer any user interaction but provided an unending stream of data. Ticker-tapes and the AP Newswire were prime examples of this generation of online service.
Second Generation: Character-Based User Interfaces
The original text-based CompuServe interface is a classic example of a second-generation online service. Most BBSs (bulletin board systems) still provide only a character-based interface. The traditional, line-oriented, interfaces to the Internet (e.g., FTP) also fall in this category. Basically, the user's only option is to type on the command line in order to select what information should be retrieved. This information is then displayed as a scrolling text, but the user cannot interact with the content of this text.
Third Generation: Retrofitted GUIs
America Online, some graphical front-ends to CompuServe, eWorld, Prodigy, many videotex services like Minitel , and the WWW (when used without dynamic content like Java applets) all essentially follow the good old IBM 3270 style of interaction: the system displays a page of information and allows the user to select an element from the page in order to get the next page (so-called asynchronous dialogue). These interfaces are often prettied up with nice icons but the user cannot really interact with the information; the only option is to select the next screen.
Fourth Generation: Fully Window-Oriented Designs
These services have been designed from the ground up by user interface professionals to provide an optimal user experience given the state-of-the-art in window-based graphical user interfaces. Current examples include AT&T Interchange and the Microsoft Network. Fourth-generation online interfaces have multiple dialogue elements on the screen at the same time and allow the user to interact with one dialogue element in order to dynamically change another.
WWW services built with Java have the potential to have fourth-generation interfaces since they can be true client-server solutions with dynamic content on the client side. It is several orders of magnitude less work to implement a Java service than to build a full-fledged online service like AOL. The upside of this simplicity is that many more companies will build services and that we will see a wider variety of ideas implemented. The downside is that the smaller scale of the projects means that many of them will not have user interface professionals on staff to drive the design. Design Darwinism will lead to some great surviving designs, though.
Fifth Generation: Data-Centered Integration
The future will bring online services that are fully integrated with the user's computational environment instead of being relegated to stand-alone applications. This move from an application-centered model to data-centered object-oriented designs might, for example, support a scenario where you receive a report by email that has a link to an Internet server that automatically updates one or two paragraphs of the report that have changed since they were written, or where you have a spreadsheet where a key number is automatically posted to your web server every time it is changed.