For users, this is what it means to be at the center: to be unaware of anything outside it. User-Centric Design means obscuring more than it surfaces.

Example 10

Essential features flow seamlessly between online and offline modes; examples include cross-references, user annotations, access to online databases, as well as licensing and rights management.

A very fundamental property to maintain in ontologies are the identity criteria. There is fundamental work by Nicola Guarino et al. about making ontological distinctions based on identity criteria, which led to the DOLCE ontology. For the Semantic Web, we must try ensure two things: a) that different parties see one thing as one, both at the same time and diachronically b) that things have well-defined properties.

all representations have essentially the same information content. And what we mean by "essentially" allows in fact some wriggle room, and in the end it rests on a common understanding between publisher of the information and quoter of the URI. The sameness we are after is the sameness of information content. That is what is identified by the URI. That is why we say that the URI identifies that conceptual information content, irrespective of its particular representation: the conceptual work. Without that common understanding, the web does not work. Some people have said, "If we say that URIs identify people, nothing breaks". But all the time they, day to day, rely on sameness of the information things on the web, and use URIs with that implicit assumption. As we formalize how the web works, we have to make that assumption explicit.

I'm sticking with the machine-processable languages as examples because human-processable ones like HTML have a level of ambiguity traditional in human natural language but quite out of place in the WWW infrastructure -- or the Semantic Web.

we must either distinguish or be hopelessly fuzzy. And is this bad, is it an inhibition to have to work our way though documents before we can talk about whatever we desire? I would argue not, because it is very important not to lose track of the reasons for our taking and processing any piece of information. The process of publishing and reading is a real social process between social entities, not mechanical agents. To be socially responsible, to be able to handle trust, and so on, we must be aware of these operations. The difference between a car and what some web page says about it is crucial - not only when you are buying a car. Some have opined that the abstraction of the document is nonsense, and all that exists, when a web page describes a car, is the car and various representations of it, the HTML, PNG and GIF bit streams. This is however very weak in my opinion. The various representations have much more in common than simply the car. And the relationship to the car can be many and varied: home page, picture, catalog entry, invoice, remote control panel, weblog, and so on. The document itself is an important part of society - to dismiss its existence is to prevent us being aware of human and aspects of information without which we are impoverished. By contrast, the difference between different representations of the document (GIF or PNG image for example) is very small, and the relationship between versions of a document which changes through time a very strong one.

It demonstrates the ambiguity of natural language that no significant problem had been noticed over the past decade, even though the original author or HTTP , and later co-author of HTTP 1.1 who also did his PhD thesis on an analysis of the web, and both of whom have worked with Web protocols ever since, had had conflicting ideas of what the various terms actually mean.

an HTTP URI may identify something with a vagueness as to the dimensions above, but it still must be used to refer to a unique conceptual object whose various representations have a very large a mount in common. Formally, it is the publisher which defines the what an HTTP URI identifies, and so one should look to the publisher for a commitment as to the exact nature of the identity along these axes.