How does PLINTH solve these problems?

• create, manipulate and browse design rationale (DR) using hypertext networks based on typed node-and-link based DR models like IBIS and DRL;

• connect document nodes to their underlying DR structures with ordinary hypertext links;

• show multiple structural, logical and rhetorical views of a single document by activating or suppressing different sets of node and link types, thus reducing the perceived complexity of the network and the reader's cognitive overhead of understanding it.

free browsing:

Here the navigator follows basic structural links like next and part-of in response to commands from the reader like next, previous, up, back, and so on, displaying the text of each node visited. Where a DR node is attached to a document node, the navigator can dip into the DR network and browsing rules for exploring this will be activated.

consultation:

The consultation facilities of conventional expert systems for regulations are achieved using navigation based on logical typing of nodes and links, e.g. requirement, scope, necessary, sufficient, applies-to and so on. In this case the navigator follows the links in logical order, assigning truth values to nodes by asking the reader whether or not the conditions expressed in the node text are met. These truth values are combined according to the link types in order to decide which requirements apply and advise the reader on how to satisfy them. This method alleviates the expressiveness, parsimony and maintenance problems:

• The texts of individual clauses need not be expressed as rules. There is no expressiveness problem with high-level functional concepts like `adequate' and `sufficient' which are difficult to represent, neither is there a parsimony problem of having to formalise clear, concise statements which do not benefit from it. However, it is sometimes useful to be able to break down clauses further, e.g. to do a calculation expressed in the text as a table or formula. For this purpose, PLINTH allows local rules to be attached to nodes and activated when the node is visited;

• Different documents with the same node and link types can use the same set of basic consultation rules (augmenting them with local rules where necessary), thus reducing the size and complexity of the rule-base and the problem of maintenance. Once those rules are written, an author without programming skills can write a new document and `program' the required logical breakdown simply by assigning types to the nodes and inserting links between them.

design rationale processing:

The process of building a DR network can be supported by navigation rules which not only traverse existing parts of the network but also allow the author to extend it in a principled manner.