Why is PLINTH needed?

PLINTH was originally designed to support the work of the Building Directorate of the Scottish Office on the Building Standards Regulations for Scotland and the associated Technical Standards.

Both hypertext and rule-based systems are well established individually as tools for work on regulations and standards. Hypertext systems provide structured access to technical documents, and can maintain and cross-reference large bodies of text, diagrams and tables. Rule-based expert systems exploit the inherently rule-oriented nature of regulations. However, both approaches have limitations:

cognitive overhead:
Hypertext has the well known problems of disorientation and digression, where readers fail to maintain a mental picture of their location and path in large networks, and get side-tracked or lost.
Expert system rules are limited in expressiveness compared with texts and diagrams. This is especially true with newer, less prescriptive regulatory documents where requirements may be expressed using terms like `adequate means' and `sufficient provision', as well as in precise weights and measures.
Conventional expert systems must reduce all knowledge to rules, whether or not this is appropriate. For example, although following the logical dependencies between clauses in regulatory documents is difficult, the individual clauses are usually expressed in clear, concise language that is quite easy to understand. This distinction can be exploited by focusing the system's intelligence on ensuring the correct and efficient use of documents, and trusting the user's intelligence to interpret their contents.
Creating large rule-bases for regulations, and maintaining the rules as the regulations are revised, is a time-consuming process requiring skilled programmers (this is partly a consequence of the parsimony problem).
design rationale:
Neither conventional hypertext nor rule-based systems are well suited to providing support for handling the design rationale (or "argumentation") underlying the technical documents, i.e. the data from research, discussion and consultation that goes into their production. The ability to structure and manipulate this information easily is very important for authors.

How does PLINTH solve these problems?