Subject: [TS] Re: Topic maps
From: Eric Freese (eric@isogen.com)
Date: Fri Mar 03 2000 - 02:06:44 EST
> Here are my thoughts on various aspects of topic maps, particularly
> where they differ from ThoughtStream.
>
> 1: Scopes
> Scopes are essentially a way to resolve name collisions. For example, a
> topic map may have two topics named "Washington", one in the scope of
> "City" and the other in the scope of "State". A user may specify a
> scope while searching a topic map in order to reduce the number of hits
> returned.
> ThoughtStream can currently simulate this by using links. Is it
> necessary to add a special case for this? One argument in favor of
> treating scopes specially is that there may be a large number of "City"
> ideas in a mind, so that the idea named "City" become overwhelmed by the
> number of links. It is a hub linking to each individual city, but any
> information specific to the "City" node is drowned out. On the other
> hand, topic map scopes are used as a filter over search results, while
> link-based scopes could be used to improve the efficiency of the search.
In your example, city and state would probably be topic types rather than
scopes. Topic types could still be used to narrow down searches. This
would also help to differentiate the links between "City" and the cities and
those that are specific to "city".
Scopes can also be used to differentiate between 2 cities with the same name
like Rome, NY and Rome, Italy. Scopes are optional.
> 2: Formally-defined link types
> Currently in ThoughtStream, there are the Parent/Child and Jump/Jump
> link types, and a user-specified label for each end of a link. In Topic
> Maps, a link type is itself a topic. This lets you define attributes of
> a link. For instance, one could declare that "located in" is
> transitive, and then this information could be used in searches or other
> operations.
> I like this concept, but I'm not sure if I want to clutter the idea
> namespace with metadata like this.
The extra info will hopefully add processing power to the links and allow
them to be more useful.
> 3: Out-of-line links
> Associations between topics are stored outside of the <topic> element.
> I think that inline links are preferable whenever possible (i.e.
> whenever it is possible to modify both ends of the link), especially on
> CPU- and memory-limited devices such as Palms. This is an
> implementation detail, but it also matters on a higher level - in
> ThoughtStream, you can[1] arrange links, notes, and other items in any
> order within an idea. In XTM, the order of links and notes relative to
> each other would be lost (order within a class of items could be
> preserved, but is not guaranteed).
I'm assuming (hoping) that you are using a data format optimized to work
within the Palm device rather than the bare XML.
If order is important, you could build links that set the order.
> 4: External data
> Information is stored in a topic map in two ways - associations, which
> link two (or possibly more? the spec wasn't clear on this) topics, and
> occurences, which are links to documents outside the topic map. In TS,
> information can be stored within the idea in the form of notes or other
> data items. There doesn't seem to be any way in the standard topic map
> format to cram this sort of data into the topic map.
Associations can link as many topics as you want, but the semantics of the
link aren't really defined. If you use the basic Topic Map structure, you
could, for example, define a note element that occurs within the topic where
the PCDATA is now. As long as you have topics, associations, themes,
scopes, etc. you should be ok to add additional structure and be compliant.
Interchange of the data may be an issue though since other topic map tools
might not be able to handle the extra data.
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