A comparative study of six French-language Web directories

Houssem Assadi and Thomas BeauvisageFrance Télécom R&D – DIH/UCE, FranceA Comparative Study of Six French-language Web DirectoriesAbstract: This paper presents a comparative study of six French-language Web directories (MSN, Nomade, Open Directory, Voila, Voila Pages Perso and Yahoo). The study focuses on the quantitative and qualitative aspects of the organization of these directories, and on the way in which they describe sites. It reveals a wide variety of structures, content and organizational principles. In this respect, Web directories do not correspond to classic theories of classification. They highlight the difficulty of proposing a structured representation of the heterogeneous content of the Web.1. IntroductionWeb directories, lists of web sites classified into categories, are extensively used by Internauts. They are particularly useful for novices since they facilitate navigation and provide particularly relevant links, especially compared to "full text" search engines with their problems of complexity of queries, noise, etc. The creation of Web directory categories and the classification of sites are done manually, which contributes to an acceptable organization of information: categories are created "rationally" and systematically, and the relevance of listed sites is generally guaranteed.We undertook a comparative study of six Web directories partially or totally dedicated to the French-language Web: MSN, Nomade, Open Directory, Voila, Voila Pages Perso and Yahoo. This study concerned data available in these Web directories in February 2001. We first developed a specific software package in order to explore the structure and content of directories (hierarchical links and cross-references between categories, listed addresses and site descriptions). On the basis of these data we then performed a qualitative analysis of the organizational principles of each directory, followed by quantitative investigations consisting of: 1) calculation of statistical indicators representing the structure and complexity of each directory; 2) calculation of the specific characteristics of each directory, based on the content and presentation of the indexed sites. Our study included other analyses based on a formal exploitation of directories as graphs, but the limited scope of this article does not enable us to include those aspects as well.2. What is a Web directory?A Web directory offers users lists of sites grouped into hierarchically structured categories forming a "tree". These categories contain the indexed sites or pages (identified by their URL, i.e. their Internet address), along with a brief description of their content.Directories differ not only in size and number of URLs presented and indexed, but also in structure. The structure of a directory can be defined by the combination of three elements: - Multi-indexing: some directories index the same URL in different categories; thus, the same address sometimes appears several times in different places in a directory.Position of the URLs indexed in the tree: some directories propose URLs in all their categories, while others classify them only in terminal categories (i.e. those which do nothave sub-categories).- Use of cross-references: directories such as Yahoo propose links, within categories, to other categories which may be situated anywhere in the directory and not necessarily directly beneath them in the tree.Structurally, each directory is thus a combination of these three elements, as presented in Table 1.Multi-indexing URLs are indexed onlyin terminal categoriesUse of cross-references MSNNomadeOpen DirectoryVoilaVoila PPYahooTable 1 - Structural description of directories3. Differences of size and structureThe first difference we observe is in the coverage of directories, calculated in terms of the number of indexed URLs. This calculation must take into account multi-indexing: if a directory lists the same URL in several places, it will present more addresses than individual URLs actually indexed. That is why it is important to distinguish between the number of URLs presented and the number of individual URLs indexed (cf. Table 2). For example, whereas Nomade is the directory with the broadest coverage (139,000 indexed URLs), Yahoo presents the highest number of URLs to the user and thus has the highest repetition rate.Directories also vary highly in terms of depth. Yahoo, with its 18-level depth tree, has the most depth. The smallest directory, Voila Pages Perso, has a maximum depth of only 5. But depth does not systematically correlate with the number of URLs (see Table 2). We furthermore found wide variability in terms of density (mean number of URLs per category). Whereas Nomade and Voila propose a mean of close to 20 URLs per category containing at least one URL, Open Directory, Yahoo and MSN offer a mean of between 5 and 10.NumberofcategoriesMaximumdepthTotalnumber ofURLspresentedNumber ofindividualURLsMean rate ofURLrepetitionNumber ofcategorieswhich indexat least oneURLMeannumber ofURLs percategorywith at leastone URL MSN 6,875 7 62,523 46,137 1.35 6,507 9.61 Nomade 9,165 10 183,590 138,832 1.32 8,754 20.97 Open Dir. 5,244 10 32,496 32,496 1 4,201 7.73Voila 8,967 10 134,502 59,744 2.25 7,854 17.12 Voila PP 601 5 50,794 27,923 1.81 564 90.06 Yahoo 44,137 18 192,160 106,832 1.8 37,178 5.17 Table 2 - Indicators of size, depth and multi-indexingFinally, cross-references strongly influence the directory structure. They facilitate navigation for the user and enable the creators of directories to compensate for the rigidity of the overall organization of the tree. The four directories that use cross-references (Nomade, Open Directory, Voila and Yahoo) do so differently (see Table 3). While Nomade and Voila make little use of them (only 1.6% of Voila categories use cross-references, with a mean of1.4 cross-references proposed), Open Directory and Yahoo use them on a big scale (20% of the Yahoo categories, with a mean of 4 cross-references per category).Total number of categoriesNumber ofcategories with across-referenceTotal number ofcross-referencesMean number ofcross-referencesper category withcross-referenceProportion ofcategories withcross-referenceMSN 6,875 - - - - Nomade 9,165 586 997 1.70 6.3%Open Dir. 5,244 526 1,660 3.15 10.0%Voila 8,967 142 202 1.42 1.6%Voila PP 601 - - - -Yahoo 44,137 8,806 34,840 3.95 19.9%Table 3 - Use of cross-references4. Web directories have different organizational principlesIn this section we consider the principles governing the organization and structuring of directories. Several models can be used for the organization of data and knowledge, derived from fields as varied as knowledge representation in Artificial Intelligence, the compilation of thesauruses (e.g. in libraries) or the creation of indexes and other "paper" directories (e.g. yellow pages, professional directories). These different models have been adopted by the publishers of Web directories, in some cases intentionally, in others less so. Three modes of organization can be distinguished:- Systematic categorization of domains of human activities, objects of daily life, etc. in an ontological approach.- Less systematic and more practical cataloguing, focused on human activities (e.g.business, recreation, various forms of sociability), in a "yellow pages" approach.- Categorization of the "Internet world": mapping of sites and services available on the Internet, without any precise criteria for classification of objects of the world, human activities, etc.Note that Internet directories, at least those that we studied, do not correspond strictly to any one of these approaches; they combine the principles of usual classificatory objects: ontologies, thesaurus, etc. In the six directories that we studied, very different organizational models were identified.For example, if we compare Yahoo and Voila, Yahoo has a systematic classification approach evident in a large number of categories (44,000 compared to 9,000 in Voila) organized in an 18-level tree structure (compared to 10 levels in Voila). Yahoo also has a very dense network based on a system of cross-references between categories (34,000 cross-references, compared to 200 in Voila). The main first-level categories in Yahoo are "Regional" (Exploration géographique) and "Business and economy" (Commerce et économie). This reveals a systematic classification approach. The encyclopaedic aspect of the Yahoo directory is also evident in the presence of categories such as "Social science" (Sciences humaines) at the top of the tree. By contrast, Voila has a pragmatic approach, focused on services related to human activities: business, social activities and recreation. This practical aspect of Voila is strengthened by the existence of a first-level category "Shopping, daily life" (Achat, vie pratique) which accounts for 13% of all indexed sites and has no equivalent at the top level in Yahoo France directory.The six directories studied index a total of 283,000 distinct URLs. We found that in general the directories overlap very little and have only 25 URLs in common; 70% of all the indexed URLs are in only one directory and 89% in one or two directories.Each directory has its specific characteristics, confirmed by a low two-to-two overlap. Since the sizes of directories differ, the calculation of two-to-two overlaps between directories is asymmetrical and must be analysed for each pair of directories (Table 4).Ðshares n % of its URL with ÎMSN NomadeOpenDirectoryVoila VoilaPP YahooMSN 100.0% 33.8% 13.2% 22.7% 1.5% 35.7%Nomade 11.2%100.0%9.3%19.7%3.4%30.4%OpenDirectory 18.8% 39.9% 100.0% 22.9% 2.4% 33.6% Voila 17.6% 45.8% 12.4% 100.0% 3.8% 37.7%VoilaPP 2.4% 16.6% 2.7% 8.0% 100.0% 8.7% Yahoo 1.4% 39.5% 10.2% 21.1% 2.3% 100.0%Key: 11.2% of URLs of Nomade are also indexed by MSN, while 33.8% of the URLs of MSN are inthe Nomade base.Table 4 - Overlaps between directoriesThe particularity of the Voila Pages Perso personal sites directory is strongly confirmedby the very low level of overlap with other directories, especially from Voila Pages Perso toother directories, even though Voila Pages Perso is the smallest directory of all.The mean overlap rate between the different directories is 18.1% and 22.8% if we exclude the very specific Voila Pages Perso. As in the case of Voila Pages Perso, size doesnot seem to be the decisive factor in overlaps between directories. For example, MSN andOpen Directory, both small, share less than a third of their URLs, on average, with other directories up to four times bigger – an overlap equivalent to that between Nomade and Yahoo, the two biggest. It thus appears that each directory indexes sites peculiar to it. This is confirmed by the proportion, in each directory, of URLs indexed in no other directory (see Table 5).Directory Number of sites indexed Number of sites peculiarto the directoryPercentage of sites peculiar to the directoryMSN 46,223 21,17445.8% Nomade 139,051 74,089 53.3% Open Directory 32,496 12,292 37.8%Voila 59,801 21,482 35.9% Voila PP 28,330 20,614 72.8%Yahoo 107,052 48,899 45.7% Table 5 - Proportion of indexed URLs peculiar to each directoryWith the exception of Voila Pages Perso, which has a particular content (73% of URLs peculiar to it), we note that Nomade, the biggest directory, is also the one with the most particular characteristics (53.3%). This result was expected. Less predictable were the rates of particularity of MSN (45.8% of URLs peculiar to it), which is three times smaller than Nomade, and Yahoo, which has few particularities despite its size. It thus seems that there is a twofold effect contributing to the particularity of directories: their size, which statistically increases their chances of indexing sites that others exclude, and their content, determined bytheir choice of indexed sites.In this part we examined the particularity of each directory in terms of content and style. We first wished to establish whether, on a given topic (e.g. art, sport or politics), different directories have marked differences in choice of content and, if so, to what extent? We excluded Voila Pages Perso from this analysis, because of its intrinsic particularity, and retained only the five general-interest directories.We qualified the content of the directories on the basis of the short descriptions they give of indexed Web sites on a given theme. The following method was applied:1. We first choose topics present at the first level, for the five directories studied;2. We then extracted, for each directory and for all the sites classified under the chosentopic, the directories' descriptions of those sites;3. The corpus thus constituted was processed with a lexicometric tool, Alceste (Reinert1993). This enabled us to identify the specific vocabulary used by each directory to describe sites on a given topic.The first topic selected was "Art and Humanities" (Art et culture ) present at the top level of the five directories. At this level MSN focuses on North American museums (specific vocabulary: "US", "Canada", "Montreal", "New York", etc.), Open Directory gives priority to downloading of music ("MP3", "server", "free", etc.), Nomade emphasizes the accessibility of art ("consult", "invite", "share", etc.), Voila is more business-oriented ("bargains", "shopping", "catalogue", "order", etc.) and Yahoo seems to be more eclectic, with a slight preference for cinema ("scenario", "critique", "synopsis", etc.).The same analysis was applied to the category "Business and economy" (Commerce et économie ), also found at the first level of the five general-interest directories. Here again, MSN focuses largely on North American sites, with particular emphasis on financial topics ("financial", "bank", "investment", "shares", etc.). Nomade seems to be oriented more towards the tourism industry ("visit", "restaurant", "rating", "hotel", etc.). Yahoo and Open Directory tend to favour international trade and the manufacturing sector ("truck", "rubber", "development", "international", etc.). Lastly, Voila's position appears to be less specific although it has a slight tendency towards local business (place names are over-represented).MSN Nomade Open Dir.Voila Voila PP Yahoo Nouns 78.5% 66.9% 73.8% 74.0% 70.6% 78.9% Verbs 5.1% 16.4% 8.4% 9.8% 12.8% 5.6% Adjectives 14.9% 12.3% 15.1% 13.2% 12.2% 14.2% P O Sm a i n c a t .Adverbs 1.5% 4.4% 2.7% 3.0% 4.4% 1.3% 1 SG 1.3% 0.9% 0.9% 0.2% 8.8% 1.0% 2 SG 9.0% 0.9% 9.6% 2.3% 3.7% 26.0% 3 SG 79.7% 51.2% 60.6% 54.3% 46.8% 57.2% 1 PL 1.0% 1.3% 2.9% 0.2% 3.6% 0.9% 2 PL 2.2% 38.3% 15.5% 34.6% 30.1% 3.5%V e r b s a np r o n o u n sp e r s o n /n u m b e r 3 PL 6.7% 7.4% 10.5% 8.5% 7.0% 11.5%Table 6 - Distribution of main POS categories and person/number for each directoryIn addition to this, we performed a part-of-speech tagging of all the site descriptions for each Web directory in order to see its stylistic specificities. We thus analyzed the distribution of main POS categories and of verbs and pronouns person/number for each directory (see Table 6). This analysis raised an opposition between two presentational attitudes: on the one hand, directories as "helpful guides", with an over-representation of verbs and the 2nd person plural (typically: "You will find on this site…"): Nomade, Voila, Voila Pages Perso; on the other hand, directories as "neutral information relay", with very few verbs and a dominance of nouns, adjectives and the 3rd person singular: MSN, Yahoo and Open Directory.7. DiscussionMost earlier studies on Web directories were undertaken by researchers and specialists in library science and documentation (Bertonèche 2001) (Chan, Xia et al. 1999) (Van der Walt 1998) (Vizine-Goetz 1996). Other studies have focused on directories as systems of reference classification, and have used them as a resource for automatic classification of documents (Mladenic 1998), (Labrou and Finin 1999). Two studies in particular attracted our attention in so far as they present a comparison of several Web directories (Bertonèche 2001), (Van der Walt 1998). In both cases the approach is purely qualitative and the findings are very close to our own, i.e. wide diversity, even heterogeneity, among the directories studied.Our study has the particularity of combining a qualitative approach ("manual" analysis of directories and critical analysis of their modes of organization), and a quantitative approach based on statistical and formal processing: exploitation of the textual content of site descriptions in directories and of the structure of the directory as a graph.Specialists in cataloguing and library science recommend taking into account the different classificatory and methodological theories developed by their disciplines, and applying them to the cataloguing of Internet sites. Our view is that this classificatory approach cannot be transposed as such to the Internet world, for at least two reasons. The first is that the Web is not an encyclopedia of knowledge and is not comparable to a library. It offers content, services and, more generally, resources of all kinds, with a very wide variety of topics and quality. The second reason lies in the diversity of contexts in which the Internet is used, and of user profiles and needs. This is a very different situation from readers in a library or other documentary resource center, whose needs can be determined a priori and whose profiles have been defined on the basis of a long history of practice.We agree with library science specialists on the need for more rigor in the construction of Web directories. We also think that general-interest Web directories, like those that currently exist, have possibly reached their limits. The management of a large number of sites and categories seems to pose problems manifested in a lack of coherence. Two areas appear to be emerging for further development of Web directories suited to current trends in their use: "regional" directories, specialized by sector of activity, geographic or cultural domain, etc., and systems based on collaborative evaluation and cataloguing of web sites within "interest communities".8. ReferencesBertonèche, J. (2001). “L'Internet-bibliothèque : accéder au savoir ou se l'approprier?” SPIRALE - Revue de Recherches en Education(28): 195-214.Chan, L. M., L. Xia, et al. (1999). Structural and multilingual approaches to subject access on the web. 65th IFLA Council and General Conference, Bangkok, Thailand.Labrou, Y. and T. Finin (1999). Yahoo! as an Ontology Using Yahoo! Categories to Describe Documents. CIKM.Mladenic, D. (1998). Turning Yahoo to Automatic Web-Page Classifier. European Conference on Artificial Intelligence.Reinert, M. (1993). “Les "mondes lexicaux" et leur logique.” Langage et société(66): 5-39. Van der Walt, M. (1998). The Structure of Classification Schemes Used in Internet Search Engines. Fifth International ISKO Conference, Lille, France, Ergon Verlag.Vizine-Goetz, D. (1996). Using Library Classification Schemes for Internet Resources. OCLC Internet Cataloging Project Colloquium, San Antonio (Texas).。