Yet another unofficial help page!
Note: This entry refers to the old DNA (Ripley) system, not Barlesque or Pliny. The structure of URLs on the new h2g2 is different.
A companion entry to A23908205.
A-numbers. These are articles. On h2g2, the oldest DNA subsite, articles are known as Guide Entries. A-numbers are unique across all DNA subsites. Unlike all other alphanumeric page types, only certain numbers are valid. The checksum is explained by Jim Lynn. Valid A-numbers will automatically become links in conversations and plain-text articles.
B-numbers. These are blobs. Older pictures on the DNA system were stored as blobs. A picture may be inserted into a GuideML article with code of the style <PICTURE EMBED="right" SHADOW="none" ALT="A dinosaur holding an egg on which is written, 'h2g2 researcher'" BLOB="B361736"/>. Newer images are stored differently, and have names instead of numbers. B-numbers are unique across all DNA subsites. B-numbers do not automatically become links in conversations and plain-text articles.
C-numbers. These form the categorisation system. Articles may be put into categories, with each article potentially being included in many different categories. C-numbers are independent across DNA subsites, with /dna/hub/C1, /dna/h2g2/C1, and /dna/actionnetwork/C1 being unrelated pages. The categorisation system for one site may contain articles located on another site. This is technologically possible, but unlikely to happen very often. C-numbers will automatically become links in conversations and plain-text articles, even on sites which do not have categorised articles. In this case, they will form broken links.
F-numbers. These are conversation fora. Each forum may contain a number of conversations. F-numbers are unique across all DNA subsites. F-numbers will automatically become links in conversations and plain-text articles. More information on conversation fora is found in the companion article, A23908205.
G-numbers. These are used for campaigns on the Action Network. G-numbers will automatically become links in conversations and plain-text articles. On sites other than Action Network, they form broken links.
T-numbers. These form threads or conversations. T-numbers are unique across all DNA subsites. T-numbers will not automatically become links in conversations and plain-text articles. More information on conversations is found in the companion article, A23908205.
U-numbers. These form user pages. Each registered member of the DNA system has a unique user number (on h2g2, these are called Researcher numbers). Each member has a page on each DNA community, but not on the DNA message boards. These numbers are thus related across DNA subsites, but not exactly the same. /dna/collective/U612575, /dna/hub/U612575, and /dna/h2g2/U612575 are all different pages, but all belong to the same person. (It's worth noting that a change was recently made in the way U-numbers work. Previously, they always had the same content across the DNA subsites, but would look different, in a manner similar to the difference between h2g2 skins. This change has had interesting effects for the attached journals and message centres, but this is getting more complicated than necessary so I'll stop.) U-numbers will automatically become links in conversations and plain-text articles, even on messageboards, where they form broken links.
The article content of each Personal Space also has an A-number (since the changes, now that Personal Spaces are different articles on different subsites, each Personal Space has several A-numbers, one for each DNA community). These A-numbers will redirect to the U-number. The Alabaster skin shows these pages in the list of guide entries (MA-page).
No double-digit articles will form auto links.
MA-numbers. These list a member's articles. The number following the MA- prefix is the same as that following the U- prefix for the same user. An extract from the user's MA- page appears on the user page (personal space).
MJ-numbers. These are members' journals. The simple MJ-number (with the same number as that following U- or MA-) will show only a link to return to the personal space (U-number page). (Example: MJ612575.) To actually display the journal, it must be followed by ?Journal=###, where ### is the forum number (F-number) of the user's journal. (Example: MJ612575?Journal=1749279.) An extract from the user's MJ- page appears on the user page (personal space).
MP-numbers. These list a member's postings. Actually, they list the conversations to which a user is subscribed. The number following the MP- prefix is the same as that following the U- prefix for the same user. An extract from the user's MP- page appears on the user page (personal space).
RF-numbers. These are review fora. A simple RF-number will display an article much the same as for an A-number. (See, for example, Peer Review, The Flea Market, and The Alternative Writing Workshop.) At the bottom of an RF-page will be, not a conversation forum, but a list of articles in that review forum. An RF-number followed by certain commands, such as RF1?entry=0&skip=0&show=25&order=lastposted&dir=0, will show only entered articles, and not the text of the RF-page itself1. RF-numbers are unique across all DNA subsites. (I've just checked all the RF-numbers from RF1 to RF29, and the only active ones are on h2g2. RF30 is not a valid id.)
TestUserPage-numbers. Replacing U with TestUserPage shows the code underlying a Personal Space.
UserEdit-numbers. Replacing A (or P) with UserEdit allows you to edit the page (if you have editing rights for that page).
Named Entries are just alphabetic, with no numbers. Named Entries are specific to each DNA subsite. Some of these are special pages, such as Info, Index, and Search. Browse is identical to C1 (and, for some reason, C889). The Logout page tells you that you've been logged out of h2g2, but doesn't actually work. The Login page directs you to the sign-in page.
Most Named Entries, though, point directly to certain A-numbers. For example, the page of Named Entries has the A-number A692903, but can equally well be produced by the name NamedEntries. Of course, /dna/mbradio4/A692903 will also work, whereas /dna/mbradio4/NamedEntries will not.
In fact, for each subsite, there is an independent list of names and the A-numbers to which they point. And those A-numbers do not have to belong to the site in question. h2g2 has some names which point to A-numbers of DNA Hub articles. One example is Versions, which points to A397343, which is a Hub article.2
Named Entries can be useful for other reasons. h2g2's newspaper, The Post, has a different front page, with a different A-number, for each issue. The name ThePost is changed by the Editors to point to the latest issue each time.