Methodology

The design of the W-KLIC system is organized into four different layers.

1. Message Layer This layer involves the generalization of the socket-based communication provided by the KLIC system. This level is used to support all the communications required at the upper layers. This layer is accessible by the user through a simple interface based on message structures and built-ins to establish communication.
2. HTTP Layer On top of the message layer we provide a complete implementation of the HTTP communication protocol---HTTP is the protocol employed to support communication in the WWW. This layer is accessible by the user through a collection of built-ins allowing to both retrieve HTML documents, given their URLs, or transmit them.

3. Object Layer The object layer offers higher level structuring to support manipulation of HTML documents as data. This layer provides, in the first place, a structured view of HTML documents. Each HTML page is represented using a tree structure (HTML-tree), where each node is labeled with the tag describing the nature of the information encoded in the corresponding subtree (e.g., enumeration, link, etc.). The connection between separate pages through hyperlinks is encoded in a graph structure called HTML-graph. The nodes of an HTML-graph are HTML-trees or other HTML-graphs.

   Common Gateway Interface (CGI) scripts are easily realizable, as they are expressed by simply indicating in the HTML-tree the name of the predicate (in the program) which implements the script.

   The availability of concurrency (and the possibility of turning concurrency into actual parallelism via pragmas) is a further advantage of W-KLIC over existing proposals (e.g., the complex scheme based on or-parallelism proposed in [4]).

4. Active Layer In the object layer links can only connect an HTML-tree to another HTML-tree. The active layer relaxes this restriction and allows links in HTML-trees to refer to W-KLIC procedures; following a link implies executing the corresponding procedure. This leads to a more dynamic view of browsing, allowing, for example to pass arguments between visited pages (and allowing the pages to adapt to the current status of the browsing session---adaptive browsing [1]).

5. External Interface Some additional interfaces are necessary in order to allow connection (CCI, Plug-in) of W-KLIC to existing applications which are necessary to support the execution in all the other layers.