News groups and articles

News is distributed by flodding the world with copies of each article, which are held everywhere for a few weeks typically and then discarded.

The news scene is in constant flux. It never looks exactly the same, in terms of which newsgroups and articles are available, ant any two points on the globe. It is tremendously succesfull, partly because it is completely decentralised and redundant.

Any article is allocated to one ro more news group, so news groups, as well as articles are objects for which names are useful. Newsgroup names are well defined,

Examples

		comp.infosystems.www
		alt.hypertext

meaning in these examples, "Coimputing: Information Systems: World-Wide Web and "Uncontrolled Alternative Groups: Hypertext".

For the world-Wide Web, newsgroup names are simply preceded by "news":

		news:comp.infosystems.www
		news:alt.hypertext

Articles

News articles are adderssed (in NNTP) in two ways. One is that they can be retrievd by their message-id. The message-id, as we have seen, has no structure, and so this method only works because an NNTP server keeps articles for a finite time, and so can keep an index of all message-ids which it has. In the event that an article has expired, there is nothing to be done. Even though the article is almost certainly archived semi-officially somewhere on the net, there is no way, from the message-id, of knowing where to find it. Typically, one has to know to which newsgroups it was posted and the date, and then look through archive site for the newsgroup in question (if you know that) for an achive file for the month in question.

Here, then, is an example of a scheme which provides retrieval with no hints, from a name which is persistent, but for which an implementation exists which relies on the objects being transitory.

The world-wide web addresses articles using their message ids, again prefixed with "news". The fact that message-ids must contain at least one "@" character makes them distiunct from newsgroup names.

Unfortunately, some NNTP servers do not in fact support retrieval by message-id evn though it is mandatory in the NNTP specification. In these cases, articles may be retrieved by newsgroup name and article number. Unfortunately, as different NNTP servers get articles at different times, the article numbers vary from server to server. The newgroup/article-numebr approach can only be used as a reference very locally.

(up to existing schemes , on to gopher)

Tim BL