Re: PLink availability/feature requests

From: Eric Armstrong (
Date: Mon Apr 23 2001 - 16:48:22 PDT

Eugene Eric Kim wrote:
> On Fri, 13 Apr 2001, Murray Altheim wrote:
> > If an editor adds a third paragraph to section four, what was,
> > say, "D3 (12)" now becomes "D4 (13)". Links made to this
> > paragraph in earlier versions of the document now point to
> > the newly added paragraph.
> Nope. The proper behavior should be that "D3 (12)" becomes "D4 (12)".

The existence of static, unique IDs makes the linking problem
as easy as "possible" to solve in the face of evolving documents.

There are a number of corollaries:
  1) The ID should ideally be globally unique.
     That requirement allows me to modify a document, while you
     do likewise, and merge our additions with a minimum of
     overlap problems. (The fact that we both created nodes in
     the same place creates a decidable problem: Should your
     change come before or after mine. But if we both create a
     node with the same ID, the issue is realistically
     undecidable: Who gets the original ID, who gets a different
     ID, and what happens as a consequence of changing the ID
     you *thought* you had created, if you are the loser.

  2) A hierarchical link may be *displayed* as A.1.B.4, but it
     can be internally *stored* as a root document (to define
     the context) and a unique ID (for the node). When that link
     is transmitted, it is the root and ID which is transferred.
     At display time, the hierarchical path is *constructed* from
     the root to the uniquely-specified node, and that path is

  3) The alternative is nasty, but possible: The hierarchical
     link is stored, along with the unique ID. Every change to
     the organizational structure causes a ripple of:
       a) All nodes affected by the change in a given document
       b) All links that reference those nodes

     The hierarchical paths are then modified in all of the
     links which reference affected nodes. Ugly, ugly, ugly.
     Especially in a distributed environment. But possible.

This archive was generated by hypermail 2.0.0 : Tue Aug 21 2001 - 17:58:05 PDT