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Subject: Re: [xtm-wg] parallel development of syntax and concept models
Ben, Thanks for this. I include your comments, as well as a paragraph from Michel, to provide a context for further questions... Jim BEN SAID... >This took me a while to grasp too. Basically, topics are nodes in >topic-map space which contain links to things *outside* of >topic-map space. They are the endpoints of association links, which >cannot point outside the topic map. MICHEL SAID The Hyperlink Perspective ===================== The "Hyperlink perspective", also (abusively) called "syntax", says basically: Topic maps are made of 2 hyperlinks: one is called topic, another one is called an association. The topic hyperlink has a supplementary property: it has name(s). The association hyperlink has a supplementary constraint: it can only connect topic links. Both hyperlinks can be scoped. That's basically it. JIM ASKS.... So, from the Hyperlink Perspective then, there are only three types of animals being talked about? things, qualifications of things, and links (also, I guess, a certain kind of thing). 1) Things are either topics (verbalizations of ineffable subjects) or (topic) occurrences - the real-world "realizations" that are relevant to a given topic; 2) Qualifications of things are statements or rules or constraints that apply to things or to links. So, for instance, the supplemental property that a topic (usually) has a name is a qualification of a thing. So, too, would be the supplemental constraint that an association (a certain kind of link, see below) must link a topic with a topic. And the ability of topics and association to be "scoped" is also perhaps a qualification. 3) A link is, for lack of a better description, that which connects two things. The two things can be (topic, topic), which are connected by a link called an association, or the two things can be (topic, occurrence ?) Is there a link that connects occurrences with occurrences? If not a direct one, can this done indirectly? Does it make sense to link occurrence with occurrence? 4) According to what Ben said above, it seems accurate to speak of a topic (possibly) "having" two kinds of links: a link to another topic inside the Topic Maps space (that is, an association), or a link from a topic (inside the Topic Map space) to something, not a topic, that lives outside the Topic Maps space. It seems that this other end of this second kind of link is an occurrence, since the standard says at one point, "Occurrences are the anchors of the topic link." THE STANDARD SAYS .... The standard gives two definitions for topic: An aggregate of topic characteristics, including zero or more names, occurrences, and roles played in associations with other topics, whose organizing principle is a single subject. also... A topic link element. The standard further says: The topic link (topic) element form is used to assign topic name characteristics and topic occurrence characteristics to a topic. and ... A valid topic link must have at least one of the following: a topic name, a topic occurrence, or a role played in an association with at least one other valid topic. So, ... JIM ALSO COMMENTS AND ASKS ... 5) There seem to be two particular ways to talk about just what a topic is: one is the familiar refrain that a topic must have at least one of the following: a name, an occurrence, or a role played in association with another topic. The other is the notion that a topic is in some sense both a "node" and a "link" between nodes, which is what Michel and Ben seemed to be suggesting today in their responses to my original questions. (Below I refer to the former as "the first way" of understanding what a topic is, and to the latter as "the second way" ....) I think it is worthwhile to keep these two ways of understanding a topic in mind, and perhaps come up with an elegant synthesis of these two ways of looking at things. Just a thought. 6) Is it fair to say that, in some sense, the topic link element form is, informally speaking, the abstract box that houses only one of the three pieces that make up a topic (in the sense of the first way of understanding mentioned above)? Specifically, one can find a topic name in the topic link element form. 7) Also, in considering the dual nature of topic as both node and link, (the second way of understanding what a topic is), is it fair to say that the topic link element form, by itself, deals with only the notion of "topic as node", and that it deals with this via the topic id or name ? That is, within the topic link element form, there is no mention of linking (between topics and topics or between topics and occurrences). Instead, the two ways to think of "topic as link" are actually specified elsewhere. Specifically, the link that connects topics with topics is specified in the association link element form, and the link that connects topics with occurrences is specified within the topic occurrence architectural form. Is this accurate? If so, it helps explain why this seems confusing (that there is no linking done or specified within the topic link element form). 8) And so, in summarizing these last thoughts, we can consider a topic either as being made up of at least one of name, occurrence, role played .... or as a "node/link" duality. When we look in the spec at the topic link element form, we can see just one piece of each of these ways of understanding topic: we can see the (optional) name in the first way of understanding, or we can see, say, the topic id as representing the node in the node/link way of understanding topic. But we can't see, *in the topic link element form itself* any of these other pieces of these two ways of understanding. Specifically, in the first way of understanding, we don't find in the topic link element form any mention of "topic as occurrence or role played ..."; and in the second way of understanding, we don't find the notion of topic as link. To complete the picture of both understandings we need to look outside the topic link element form itself. Is all this accurate? 9) The notion of "topic as link" in the "node/link" duality way of understanding topics, seems to be partly dealt with in the topic occurrence [element form?]. It is here where one kind of link is treated - the link between a topic and its occurrence. This same topic occurrence [element form] seems also to deal with the second of the three pieces (i.e., occurrence) in the first way of understanding a topic - that a topic consists of a name, an occurrence, or a role played ..... Is this accurate? 10) The rest of the "topic as link" in the "node/link" duality way of understanding topics, seems to be dealt with in the association link element form. (I have some questions about just how such a link is established between topics using this form, but ...) What is still dangling for me is the missing piece of "role played in association with other topics" in the first way of understanding what a topic is. 11) What is the key insight behind the association role that makes it, in the first way of understanding what a topic is, such a key component? And how does an association role relate to the "node/link" way of understanding topics, if at all? So, in thinking of a topic as both a node and a (topic) link (element form), we note the following (this should all be understood as a question; please correct me where I'm wrong): *) a topic as node can be seen as an id or name, via the topic link element form *) a topic as link can be seen partly in the topic occurrence [element form??]. This link connects topics (inside the topic map) to occurrences (things outside the topic map). A topic as link can also been seen partly in the association link element form. This kind of link connects topics to topics. *) The topic's name will live in the topic link element form, but the (description of a) topic occurrence will be treated in its own area, in the topic occurrence [element form?]. The "role played in association with other topics" also lives outside the topic link element form, in the association role element form. For those who've read this far, ... first, thanks. Second, ... I'm trying to understand things. Please comment on whether what I wrote makes sense and whether it actually sheds any light on things, or whether there are better ways of getting a grip on just what a topic is. Finally, does any of this help the discussion of "one model, two perspectives?" I suspect it may not contribute directly to that, since it seems preoccupied with the Hyperlink perspective. But maybe those who know, will see some distinctions worth making in the Foundation Perspective. Thanks for any light you care to shed. Jim -------------------------- eGroups Sponsor -------------------------~-~> GET A NEXTCARD VISA, in 30 seconds! Get rates of 2.9% Intro or 9.9% Ongoing APR* and no annual fee! Apply NOW! http://click.egroups.com/1/7872/4/_/337252/_/967501234/ ---------------------------------------------------------------------_-> To Post a message, send it to: xtm-wg@eGroups.com To Unsubscribe, send a blank message to: xtm-wg-unsubscribe@eGroups.com
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