NOV (computers)
Encyclopedia
NOV, or News Overview, is a widely deployed indexing method for Usenet
articles, also found in some Internet
email
implementations. Written in 1992 by Geoff Collyer
, NOV replaced a variety of incompatible indexing schemes used in different client programs
, each typically requiring custom modifications to each news server
before they could be used. In modern NNTP
implementations, NOV is exposed as the XOVER command.
. Tab (ASCII
code 9) characters and line breaks within the headers are converted to spaces (ASCII code 32), and the header fields within each overview line are then delimited by tab characters.
The first seven fields in a NOV line are fixed and unlabeled:
The header lines are those defined in either RFC 2822 or RFC 1036. If data for any of these fields is missing, a tab alone is put in its place. The value of the size field is approximate, as servers may count line endings as one or two characters. Additionally, the lines value may be calculated by the server, supplied by the message sender, or omitted altogether.
An arbitrary number of additional fields may be added to any NOV line. The eighth and later fields must be labeled in the form "Header-Name: contents", again delimited by tabs. The order and presence of additional fields are allowed to vary from line to line, and from server to server. Some server provide a schema of what is recorded to new overview lines in the form of an NNTP LIST OVERVIEW.FMT command, but this cannot be relied upon to be accurate for older entries.
In practice, most servers supply only one optional field, the contents of the Xref: header, to allow crosspost
management.
software employs NOV, it has also found its way into other applications such as email clients. One prominent example is Gnus
, which can take advantage of overview files for faster access to large mail folders.
Many newer news servers store NOV data in a variety of formats. A specialized database
is frequently used in favor of the original flat file arrangement.
Usenet
Usenet is a worldwide distributed Internet discussion system. It developed from the general purpose UUCP architecture of the same name.Duke University graduate students Tom Truscott and Jim Ellis conceived the idea in 1979 and it was established in 1980...
articles, also found in some Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
Email
Electronic mail, commonly known as email or e-mail, is a method of exchanging digital messages from an author to one or more recipients. Modern email operates across the Internet or other computer networks. Some early email systems required that the author and the recipient both be online at the...
implementations. Written in 1992 by Geoff Collyer
Geoff Collyer
Geoff Collyer is a Canadian computer scientist. He is the senior author of C News, a protocol-neutral news transport, and the designer of NOV, the News Overview database used by all modern newsreaders....
, NOV replaced a variety of incompatible indexing schemes used in different client programs
Client (computing)
A client is an application or system that accesses a service made available by a server. The server is often on another computer system, in which case the client accesses the service by way of a network....
, each typically requiring custom modifications to each news server
News server
A news server is a set of computer software used to handle Usenet articles. It may also refer to a computer itself which is primarily or solely used for handling Usenet. A reader server provides an interface to read and post articles, generally with the assistance of a news client. A transit...
before they could be used. In modern NNTP
Network News Transfer Protocol
The Network News Transfer Protocol is an Internet application protocol used for transporting Usenet news articles between news servers and for reading and posting articles by end user client applications...
implementations, NOV is exposed as the XOVER command.
Operation
In its original implementation, the header lines of each incoming message are examined, and a single line of text is appended to the overview files, with one overview file present for each newsgroupNewsgroup
A usenet newsgroup is a repository usually within the Usenet system, for messages posted from many users in different locations. The term may be confusing to some, because it is usually a discussion group. Newsgroups are technically distinct from, but functionally similar to, discussion forums on...
. Tab (ASCII
ASCII
The American Standard Code for Information Interchange is a character-encoding scheme based on the ordering of the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that use text...
code 9) characters and line breaks within the headers are converted to spaces (ASCII code 32), and the header fields within each overview line are then delimited by tab characters.
The first seven fields in a NOV line are fixed and unlabeled:
- Subject: header contents
- From: header contents
- Date: header contents
- Message-ID: header contents
- References: header contents
- Size of the article in octetOctet (computing)An octet is a unit of digital information in computing and telecommunications that consists of eight bits. The term is often used when the term byte might be ambiguous, as there is no standard for the size of the byte.-Overview:...
s - Lines: header contents
The header lines are those defined in either RFC 2822 or RFC 1036. If data for any of these fields is missing, a tab alone is put in its place. The value of the size field is approximate, as servers may count line endings as one or two characters. Additionally, the lines value may be calculated by the server, supplied by the message sender, or omitted altogether.
An arbitrary number of additional fields may be added to any NOV line. The eighth and later fields must be labeled in the form "Header-Name: contents", again delimited by tabs. The order and presence of additional fields are allowed to vary from line to line, and from server to server. Some server provide a schema of what is recorded to new overview lines in the form of an NNTP LIST OVERVIEW.FMT command, but this cannot be relied upon to be accurate for older entries.
In practice, most servers supply only one optional field, the contents of the Xref: header, to allow crosspost
Crossposting
Crossposting is the act of posting the same message to multiple information channels; forums, mailing lists, or newsgroups. Crossposting is perceived as inconsiderate, poor etiquette and is banned from Usenet newsgroups and virtually all email lists...
management.
Variations
While virtually all modern news server and newsreaderNews client
A newsreader is an application program that reads articles on Usenet . Newsreaders act as clients which connect to a news server, via the Network News Transfer Protocol , to download articles and post new articles...
software employs NOV, it has also found its way into other applications such as email clients. One prominent example is Gnus
Gnus
Gnus is a message reader running under GNU Emacs and XEmacs. It supports reading and composing both news and e-mail.Gnus blurs the distinction between news and e-mail, treating them both as "articles" that come from different sources. News articles are kept separate by group, and e-mail can be...
, which can take advantage of overview files for faster access to large mail folders.
Many newer news servers store NOV data in a variety of formats. A specialized database
Database
A database is an organized collection of data for one or more purposes, usually in digital form. The data are typically organized to model relevant aspects of reality , in a way that supports processes requiring this information...
is frequently used in favor of the original flat file arrangement.
External links
- Original NOV software distribution (mirror at Funet, formerly hosted at ftp.std.com)
- RFC 2980 describes the XOVER command.