Enabling Dissemination of Meta Information in the Usenet Framework
The paper discusses a transparent and flexible way to disseminate meta information within the global conferencing system, Usenet news. Examples of such information are ratings for Usenet articles or information about the behavior of other users. In particular, the paper describes how the Usenet "overview'' mechanism was modified to disseminate meta information to off-the-shelf Usenet clients. Experiences with the modified overview mechanism are discussed by example of two fully working prototype implementations disseminating social navigation information and collaborative filtering ratings to Usenet clients.
The global conferencing system Usenet news is by far the largest online system of its kind, serving the information needs of tens of thousands of users every day. In May 2001, Usenet users were contributing about a million articles every day, producing network traffic of more than a 100 Gbytes per day.
Despite its enormous growth since the early 1980s, Usenet has reached an outstanding level of reliability and fault tolerance. A significant contribution to reaching this reliability can be attributed to the fact that the global conferencing system is built on widely acknowledged standards for all of its key components. Examples are the standard format of Usenet articles [Horton and Adams 1987] and the standard way to disseminate articles based on the Network News Transfer Protocol (NNTP) [Kantor and Lapsley 1986]. Accounting for these technology-independent standards, news servers and news clients running on a variety of operating systems are able to cooperate without interfering with each others' technology.
While efficiency and reliability of news servers have improved significantly over the years, moderate progress in news client technology can be observed. State-of-the-art Usenet clients have reached a high level of reliability but most client interfaces do not appear to have been touched by recent research in information retrieval, information visualization or computer-human interaction. Most Usenet clients still offer little more than keyword-based filtering of discussions and rather primitive visualizations of discussion threads.
This lack of progress in news client technology is astonishing because the global conferencing system has been subject to a variety of research projects ranging from information filtering projects (e.g. [Morita and Shinoda 1994, Lang 1995, Mock 1996, Terveen et al. 1997, Lueg 1998]) to investigations of Usenet communication traffic (e.g. [Whittaker et al. 1998, Smith 1999, Sack 2000, Smith and Flore 2001]). Most of these research projects investigated Usenet's visible "output'' in terms of articles but they rarely fed results back to Usenet in the sense that research results were used to develop the global conferencing system.
Some interesting work in human-computer interaction has also been done in the context of Usenet newsgroups, ranging from early work in virtual newsgroups [Fischer and Stevens 1991] and groundbreaking work in collaborative filtering [Resnick et al. 1994] to more recent work in filtering agents [Sarwar et al. 1998] and social navigation support [Lueg 2000]. See [Lueg and Fisher 2002] for an overview.
Despite limited direct impact, experiences with collaborative filtering, interactive filtering and social navigation in Usenet newsgroups suggest that such approaches indeed provide benefit to Usenet users. Moreover, Usenet has shown to be a huge and fascinating social information space providing an exciting environment for research in information filtering and social navigation. However, experiences also indicate that it may be difficult to incorporate novel technologies into the Usenet framework.
From a research point of view, the question is how the incorporation of novel approaches into the Usenet framework could be made easier. A related, more general question is how the global conferencing system could become more accessible to researchers not familiar with Usenet.
This paper addresses the problem that the Usenet framework does not provide support for the dissemination of meta information in addition to Usenet's own communication traffic. Recent approaches in human-computer interaction, such as social navigation and collaborative filtering, depend on the dissemination of meta information, such as information about the behavior of other users in the case of social navigation or ratings in the case of collaborative filtering.
From a technical perspective, the problem is that Usenet is a large infrastructure consisting of many servers and user agents communicating according to fixed protocols. Such an infrastructure is difficult to change because all components need to be changed at the same time; otherwise, old components may break down if they are provided input they are not able to handle. As it is hardly possible to change Usenet as a whole, we looked at Usenet's technical foundations to find a way to disseminate meta information within the Usenet framework.
First the paper discusses some of the technical issues involved in disseminating meta information within Usenet. Next, it describes how Usenet's "overview'' mechanism was modified so that it can be used to disseminate meta information. Two prototype systems using the modified overview mechanism to disseminate collaborative filtering ratings and social navigation information are discussed. The paper concludes with a discussion of some open issues and future research directions.
In its current form, the Usenet framework does not explicitly support the distribution of meta information, such as collaborative filtering ratings and social navigation information, in addition to Usenet's own information. Accordingly, new ways had to be found to disseminate such information. We found that two of the "standard'' approaches that work well in other domains, such as the Web, do not meet the specific characteristics of the global conferencing system. The two standard approaches are introducing additional meta information distribution channels and adding meta information to documents that are already being disseminated.
Introducing additional distribution channels, such as additional augmented protocols (e.g. [Maltz 1994]), involves the problem that tools used to access modified information sources must be capable of using the additional capabilities. Experiences made in the context of collaborative filtering of Usenet articles [Resnick et al. 1994] suggest that it is hard to introduce modified versions of existing tools to a large and diverse group of users. Experiences made in the context of groupware also indicate that it is unlikely that many users are willing to adapt to new tools if the benefit of using them is unclear (e.g. [Grudin 1988]).
The second approach, i.e., adding meta information to documents that are already being disseminated, is discouraged in the realm of Usenet newsgroups. While modifying documents works fine in uni-directional domains like the Web (e.g. [Barrett et al. 1997]), it is likely to cause consistency problems in the multi-directional Usenet environment. It is a specific characteristic of the global conferencing system that articles are being disseminated among news servers on a ``flood-fill'' basis. Flood fill means that all servers offer all newly arrived articles to all other news servers they are exchanging articles with. In order to avoid inconsistencies, strict rules exist as to which party is allowed to make changes to Usenet articles. Roughly, only the server first accepting an article for distribution, i.e., where an article ``enters'' Usenet, is allowed to add certain information, such as Path:, Message-ID:, and Date: headers, to an article. Transit news servers are only allowed to add their own identity to the Path: header to indicate that the article has passed through their sites. Listing server identities in the Path: header is used to prevent that the same article is being offered multiple times to a server. Modifying articles by adding meta information would cause inconsistencies as different articles with the same unique Message-ID: identifier would be around.
Any approach to disseminate meta information in the Usenet framework should be in line with current Usenet standards. Furthermore, the information should be available even to off-the-shelf clients which means that being able to access the information should not require in-depth modifications.
The global conferencing system Usenet is based on a client-server model in which one or more news clients request articles from a dedicated news server (Figure 1). News servers are central repositories where news articles are collected and stored. To disseminate new articles, clients have to submit articles to a news server that then disseminates the articles to peer news servers.
Figure 1. Usenet's client-server model involving one or more news clients requesting articles from a news server. Apart from serving clients, the server exchanges articles with other news servers that are not included
When a user wants to read a particular newsgroup, his or her news client has to connect to a news server and request a list of the articles available in that newsgroup. Once received, the list of articles is presented to the user (see Figure 2 for an example). The user then selects a single article which is in turn requested by the client from the server. Finally the article is displayed to the user.
Figure 2. The news client Knews visualizes the discussions available in a particular newsgroup (Knews is courtesy of Karl-Johan Johnsson)
Most current news servers maintain a dedicated "overview'' database in which only selected article properties, such as article titles (Subject: headers), author identifications (From: headers), and unique article identifiers (Message-ID: headers) along with some other information (so-called "overview data''), rather than full articles, are stored. When a client requests the list of articles in a newsgroup from a news server, the server uses its overview database to provide the information requested. The benefit of using overview data is that the size of an article's overview data is much smaller than the size of the full article. This means that although maintaining an overview database implies additional processing overhead for news servers, it is still a quick and resource-friendly way to provide clients with an overview of a newsgroup. Neither the news server nor the news client have to scan the full articles in order to collect the information required.
Our research indicates that the "overview data'' concept is flexible enough to be used for the dissemination of meta information in addition to Usenet's regular information. Moreover, meta information transported as part of the overview data should be accessible by all clients that are in line with current Usenet standards (see below for experimental verification).
When a user starts to read a particular newsgroup, roughly the following communication between the user's news client and the news server takes place (Figure 3):
- The client requests overview data describing the articles available in the currently selected newsgroup by issuing an xover command to the server.
- The server returns the overview data as requested.
Figure 3. Most clients request "overview data'' from a news server in order to provide users with an overview of the articles available in a newsgroup. Full articles are only requested on the user's selection
Clients can request a description of the overview data format by issuing a list overview.fmt command to the news server. The following listing of a telnet session shows the format description as returned by the news server news.ifi.unizh.ch. The news client requesting the data is emulated by manually connecting to the server's NNTP port, which is the standard port to be used by news servers and news clients.
<lueg@padma><514 ist>telnet news.ifi.unizh.ch NNTP Trying 22.214.171.124... Connected to sifnos.ifi.unizh.ch. Escape character is '^]'. 200 news.ifi.unizh.ch InterNetNews NNRP server INN 2.2.1 25-Aug-1999 ready (posting ok). list overview.fmt 215 Order of fields in overview database. Subject: From: Date: Message-ID: References: Bytes: Lines: Xref:full . quit 205 . Connection closed by foreign host. <lueg@padma><515 ist>
Internally, the format is kept in a regular file:
<news@sifnos><45> cat overview.fmt ## $Revision: 1.3 $ ## overview.fmt - format of news overview database ## Format ## <header> ## <header>:full ## header is a news article header, known by innd. If ":full" appears, ## then header name will be prepended. Order of lines is important! Subject: From: Date: Message-ID: References: Bytes: Lines: Xref:full <news@sifnos><46>
The description of the overview format lists the elements of the overview data as well as their particular sequence. The sequence is important as only the Xref header is sent along with an unique identifier (indicated by the additional full keyword). After parsing the format description, clients know about the structure and the semantics of the data that will be returned when requesting overview data for a newsgroup.
The following listing of a telnet session shows overview data returned by the news server news.ifi.unizh.ch. The command group ifi.general was used to enter the newsgroup ifi.general and the command xover 1246 was used to retrieve the overview data describing article 1246. As described by the overview data format, overview data returned after the 224 data follows notification in line 8 consists of the internal number, the Subject: header ([Brownbag] ... ), the From: header (Verena Vanessa Hafner ...), the Date: header (Tue, 10 Apr 2001 ...), the Message-ID: header (<Pine ... @ludwig.ifi.unizh.ch>), and some more information (C: denotes what the client requests, S: denotes what the server returns).
C: telnet news.ifi.unizh.ch NNTP S: Connected to sifnos.ifi.unizh.ch. S: Escape character is '^]'. S: 200 news.ifi.unizh.ch InterNetNews NNRP server INN 2.2.1 25-Aug-1999 ready (posting ok). C: group ifi.general S: 211 4 1244 1247 ifi.general C: xover 1246 S: 224 data follows S: 1246 [Brownbag] Thursday, April 12, 12:30, Minoru Asada Verena S: Vanessa Hafner <firstname.lastname@example.org> Tue, 10 Apr 2001 13:59:32 +0200 S: <Pine.SOL.email@example.com> S: 2218 39 Xref: news.ifi.unizh.ch ifi.general:1246 ethz.general:333 S: unizh.general:149 de.sci.informatik.ki:5043 S: . C: quit S: 205 . S: Connection closed by foreign host.
Based on the overview data received, a news client can generate a list of articles currently available in the newsgroup (see Figure 2 for an example). Before presenting the list to the user, the client may apply user-defined actions, such as highlighting or removing certain articles. In addition, most clients consider the articles already read by the user so that only new articles are listed.
The next step is that the news client waits for the user to select a specific article for further reading. Only upon selecting a particular article does the client fetch the full article:
- The client issues an article command along with some other information to the server to request a full article.
- The server returns the full article as requested.
Finally, the client presents the full article to the user. The process of selecting and fetching articles continues until the user decides to change to another newsgroup or to quit the news reading session.
A commonly used news server was modified to implement extended overview data, i.e. overview data that may be used to disseminate additional meta information. First, the modification of the overview mechanism itself is described. Then, compatibility of the extended overview implementation to the standard overview mechanism is discussed. Finally, the paper describes how the modified news server has been extended to be able to retrieve meta information from external information sources, such as a collaborative filtering system providing ratings for Usenet articles.
The regular overview mechanism along with its separation of data and data format description is flexible enough to be extended to include additional data fields. The use of specific headers allows news clients to distinguish regular overview data from overview data belonging to other application contexts. For example, an advanced news client may look for Navigation: headers providing information that is useful for social navigation purposes while Recommendation: headers providing collaborative filtering ratings are ignored by the client.
The following example shows how a news server informs clients about additional information available when a description of its overview format is requested. As in previous examples, communication between client and server is emulated by using telnet to talk to the server (C: is what the client requests, S: is what the server returns):
<lueg@padma><42> C: telnet news.ifi.unizh.ch NNTP S: Trying 126.96.36.199... S: Connected to sifnos.ifi.unizh.ch. S: Escape character is '^]'. S: 200 news.ifi.unizh.ch InterNetNews NNRP server INN 2.2.1 25-Aug-1999 ready (posting ok). C: list overview.fmt S: 215 Order of fields in overview database. S: Subject: S: From: S: Date: S: Message-ID: S: References: S: Bytes: S: Lines: S: Xref:full S: SELECT-Rating:full S: . C: quit S: 205 . S: Connection closed by foreign host. <lueg@padma><43>
The following example of actual overview data shows specific rating information that is stored in the SELECT-Rating: header:
<lueg@padma><43> C: telnet news.ifi.unizh.ch NNTP S: Connected to sifnos.ifi.unizh.ch. S: Escape character is '^]'. S: 200 news.ifi.unizh.ch InterNetNews NNRP server INN 2.2.1 25-Aug-1999 ready (posting ok). C: group ifi.general S: 211 5 1233 1247 ifi.general C: xover 1246 S: 224 data follows S: 1246 [Brownbag] Thursday, April 12, 12:30, Minoru Asada Verena S: Vanessa Hafner <firstname.lastname@example.org> Tue, 10 Apr 2001 13:59:32 +0200 S: <Pine.SOL.email@example.com> S: 2218 39 Xref: news.ifi.unizh.ch ifi.general:1246 ethz.general:333 S: unizh.general:149 de.sci.informatik.ki:504 SELECT-Rating: high S: . C: quit S: 205 . S: Connection closed by foreign host. <lueg@padma><44>
News clients looking for SELECT-Rating: meta information may use the additional information provided. For example, a SELECT-Rating:-aware client may filter all articles that received low ratings while highlighting all articles that received a SELECT-Rating: high rating. Other clients would simply ignore the information.
Extended overview data should not require modifications of clients to cope with the additional information as modifying the overview data format is in line with the current NNTP standard. Additional information should not cause problems with clients that are compatible with the NNTP standard. In general, clients should simply ignore any fields they do not know.
To implement "extended overview data'' an InterNetNews (INN) news server, probably the most widely used news server today, was modified. A technical problem was that in the case of INN, the overview.fmt file is not only used to provide information to clients but the file also determines the structure of the server's internal overview database. Adding an additional overview header to this file would therefore affect the structure of the server's overview database, which would be an unwanted side-effect. The server's NNRPD daemon, which is responsible for communication with clients, was therefore modified in such a way that the extended overview format is only propagated to clients. In the case discussed above, the SELECT-Rating: header is transparently "inserted'' when sending the overview data format to clients. Figure 4 shows at what point the header is inserted into the communication between news clients and news server.
Figure 4. Most clients request "overview data'' from a news server in order to provide users with a brief overview of the articles currently available in a newsgroup. We use overview data to disseminate meta information to news clients
When investigating compatibility of "extended overview'' to existing installations, two cases were distinguished. First, we investigated whether currently available news clients are able to handle extended overview at all (e.g. whether they crash when receiving extended overview data instead of regular overview data). Tests with a variety of news clients, such as Knews and the most popular Netscape Messenger, suggest that sending additional meta information as part of the overview data does not present problems with current implementations.
Second, we wanted to know to what extent current clients are able to make use of additional information provided as extended overview data. Providing additional overview headers is in line with current Usenet standards but we were unsure how many clients would actually notice the additional information. Tests suggest that few clients consider the format of a server's overview data even though changing the format is in line with the current NNTP standard. Most clients do not retrieve the overview.fmt file in order to check a server's overview format. The reason is probably that overview data has not yet been used to distribute application-specific data. However, the fact that many news clients actually provide mechanisms to deal with overview data, such as article filtering based on overview data, suggests that being able to handle extended overview data is just a question of becoming aware of the information.
To make use of information sources, such as databases or recommender systems, external to the news server, we implemented a generic Perl-based interface. The interface is accessed whenever dedicated clients request overview data. Whether a client needs access to external information sources at all is determined when authenticating to the news server.
Adding a Perl interface is in line with the current INN design as the server already offers several Perl interfaces that allow for customized news filtering and client access verification. During our experiments (see below for a brief description), we did not experience significant performance problems. This is a subjective assessment and is not based on performance measurements. The point is that accessing news often involves some kind of delay and we did not notice additional delays.
Two fully implemented systems that use "extended overview data'' to disseminate social navigation information and collaborative filtering ratings to news clients are discussed below.
The idea of social navigation is roughly to support users in navigating information spaces by providing information about the activities of other users. Behaving in a particular way influenced by the activity of others would then be an instance of social navigation [Dourish and Chalmers 1994]. Concrete examples of social navigation are selecting a specific Web page or a particular Usenet article for reading because others made similar selections. A broad overview of the social navigation field can be found in [Munro et al. 1999].
We developed support for social navigation in Usenet newsgroups. The social navigation tool CollabNews [Lueg 2000] helps users find interesting discussions by indicating which discussions were read by other newsgroup participants. Usually this information is unavailable as reading articles, as opposed to posting new articles, is a hidden activity in the realm of newsgroups. Visualizations of these hidden activities provide valuable insights into the social dynamics within newsgroups as well as into the particular interests of individual newsgroup users who are willing to share information about their news reading behavior with other newsgroup users.
Figure 5 shows how social navigation information is provided to clients by propagating the information as part of the overview data. In this particular implementation, the news server queries a trace database where information about the news reading behavior of individual users is collected. At the end of every single news reading session, the news server submits collected reading data to the trace database. Upon request, the database returns the information
(typically, if a specific article was read by a particular user) and the server inserts the information into the overview data to be sent to clients, as shown in Figure 4. Clients can then use the information according to their built-in filtering and visualization capabilities. For example, articles could be highlighted in different colors according to who reads the articles.
Figure 5. Providing social navigation information to regular news clients by injecting the information into the overview data that is sent to the clients. In this example, the news server uses the Perl interface to access an external database containing social navigation information
Collaborative filtering [Goldberg et al. 1992] aims to provide users with specific information that helps them choose among available alternatives. The idea is that users help each other to distinguish between high quality and low quality items by providing ratings for items they have investigated. These ratings are collected and can then be used by others to focus on those items collectively rated best (or at least rated acceptable). Collaborative filtering has been implemented for various domains ranging from Usenet articles to music and videos (see [Resnick and Varian 1997] for a broad overview).
Figure 6 shows how rating information requested from a collaborative filtering system is provided to news clients by propagating the information as part of the overview data. In this implementation, the news server connects to the SELECT collaborative filtering system [Alton-Scheidl et al. 1999] and sends a list of message-IDs generated from overview data describing the articles in the current newsgroup. The SELECT server generates ratings for the articles and returns a list of ratings for the message-IDs. This information is then inserted by the news server into the overview data sent to clients, as shown in Figure 4. Clients can then use the information, for example, to filter all articles that received low ratings and to highlight articles that received reasonably good ratings.
To generate the collaborative filtering information, the SELECT server processes trace data describing the news reading behavior of individual users. The trace data is collected by the news server and is delivered to the SELECT server at the end of single news reading sessions. In the current implementation, the news server submits information indicating how much time the user spent reading specific articles, as reading time has been identified as a good indicator of user interests [Morita and Shinoda 1994].
Figure 6. The news server uses the Perl interface to request rating information from a SELECT collaborative filtering server. Communication is based on HTTP
The paper has presented a transparent and flexible means to provide off-the-shelf news clients with user-specific information. A specific characteristic of the approach is that it builds on existing Usenet standards while offering further opportunities for application-specific extensions.
The examples discussed show that using overview data to distribute meta information to news clients is a promising direction. Clearly, there is still a long way to go from a couple of prototypical implementations to a widely used method for distributing meta information to news clients from news servers. However, increasing interest social navigation and collaborative filtering can be expected to foster interest in such an extension.
Clearly, a server-centered approach such as the one discussed has certain limitations. Users have to use a particular news server as information from external sources are not propagated to peer news servers (for good reasons). This also means that users participating in a social navigation setting have to access the same news server. We consider these limitations to be reasonable as NNTP allows users to access remote servers independently of their physical location. The only design alternative would be to introduce a whole infrastructure similar to the Better Bid Bureaus developed by [Resnick et al. 1994]. Then again, significant modifications of clients would be required, which is exactly what we wanted to avoid.
Future work includes investigating what kind of information is most useful when browsing Usenet newsgroups, and how this information could be encoded in such a way that most off-the-shelf clients can act on the information using built-in filtering capabilities. Related to this is an investigation of the benefit of providing templates for inserting user-specific information into the overview data and the preparation of a well documented reference implementation.
The technical work reported in this paper was done while the author was with the AI-Lab, Department of Information Technology at the University of Zurich, Switzerland. Funding was provided in part by the Swiss Federal Office for Education and Science under contract BBW No. 98.0065 (SELECT project in the EU Framework IV / Telematics Programme). The author is grateful to Rolf Pfeifer for providing a stimulating research environment in Zurich, to Jim Underwood for his ongoing support in Sydney, and to Jacob Palme, Igor Hawryszkiewycz and the anonymous reviewers for helpful comments on draft versions of this paper. Some of the figures were originally published in the Proceedings of the Annual Conference of the Computer Human Interaction Special Interest Group of the Ergonomics Society of Australia (OZCHI 2000) and are reproduced with permission.
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