OpCit e-Services

Simon Kampa


The e-Services framework was constructed under the OpCit project with the purpose of providing advanced services over literature data. OpCit provides extensive citation linking over a large collection of papers in the physics discipline (as well as some citation-based services with citebase), which provide scholars with a unique method of efficiently browsing related literature. The e-Services framework extends this functionality by enabling researchers to further understand the relationships between literature, by, for example, requesting the significant papers or a visualisation of their relationships.

Like citebase, the e-Services framework uses the OAI interface to contact various e-print services and download the literature metadata. It then provides advanced services, such as simple visualisations (e.g. number of e-print deposits each year), co-citation visualisations (uses the co-citedness of papers as a proximity measure when plotting papers on a graph), and knowledge services (e.g. most significant papers).

The Software

The e-Services software runs as a collection of Perl scripts and a mySQL database. It is accessed through a Web interface (with the CGI protocol). The knowledge services are presented as text (and links), the simple visualisations as GIF images and SVG documents, and the co-citation visualisation as interactive SVG graphs. Figure 1 illustrates the general architecture of the e-Services framework.

Figure 1: e-Services architecture

How it was used

The e-Services framework was populated with the entire collection of papers in the arXiv archive (currently over 200,000). This provided a large base for which to test the service and, importantly, create large and detailed co-citation maps. However, this size also caused several problems. Firstly, the large dataset caused computation to slow significantly. Secondly, due to erroneous or missing citations, some of the co-citation visualisations failed to portray a convincing or useful pattern.


The e-Services administrator decides which e-print archives the e-Services framework contacts and collects metadata from. When the metadata has been collected, the archive is listed and users can select it to explore it further. In Figure 2, the user selects one of the known archives to explore.

Figure 2: Select an archive to explore

Once an archive has been selected, the user can select general (overview) services about it (Figure 3). These services provide answers and graphs on the entire archive, rather than just a single instance.

Figure 3: Overview Facilities available

Figure 4 illustrates a graph of the publications (deposited) each year for the archive.

Figure 4: Publications per year

Figure 5 illustrates a graph of the highest publishing researchers in the archive.

Figure 5: Highest publishing researchers

The significant papers (based on citation impact) have been computed for the current archive and presented as a list of linked papers (Figure 6). By selecting a paper, further information on the paper can be retrieved (e.g. author, abstract, co-citations).

Figure 6: Significant papers

The green-coloured menu on the left of the screen provides links to all instances of a particular type. In Figure 7, all instances of literature in the archive are presented.

Figure 7: List of literature

When a particular literature instance is selected, further information on that paper is presented (Figure 8)

Figure 8: Services available for a paper

When a particular researcher instance is selected, further information on that researcher is presented (Figure 9)

Figure 9: Services available for a researcher

When the collaborators for the researcher listed in Figure 9 are requested, five peers are suggested (Figure 10).

Figure 10: Collaborators

Figure 11 illustrates a small view of a co-citation map for the current archive. Each node represents a paper. An arc between two nodes indicates that these two papers are highly co-cited. A node can be clicked on to enable the user to find out more about a particular paper (e.g. Figure 8).

Various options are available for presenting these graphs. The refinement level determines the number of iterations of the co-citation algorithm. A higher level results in a more "tree-like" (and therefore more effective) graph. The threshold level determines which co-cited papers are included. A level of 10, means that only those papers that have been co-cited at least 10 times are included in the computation. A lower level results in more nodes on the graph, at the expense of greater computational overhead. The graph can also be viewed inside the e-Services interface, or full-screen in its own browser window. Finally, papers that have been recently highly cited, can be marked in red, to help researchers spot active research areas.

Figure 11: Co-Citation (small view)

A full-screen co-citation map is presented in Figure 12.

Figure 12: Co-citation (large view)

A full-screen co-citation map of the entire arXiv collection is illustrated in Figure 13. Unfortunately, due to the imperfect citation data, as well as the incredible computation power required to produce highly refined graphs, the map is less than perfect.

Figure 13: Co-citation (large view) - all of arXiv

A more refined and lower threshold (full-screen) co-citation map of the entire arXiv collection (Figure 14).

Figure 14: Co-citation (large view) - all of arXiv

When a co-citation map is produced by selecting the co-citation icon from a literature instance page (e.g. Figure 8), then the resulting map provides a beacon to display where in the map the literature instance is located (Figure 15).

Figure 15: Co-citation (context beacon)

As part of the simple visualisation services, a citation network can be produced (Figure 16). This interactive SVG map presents cited and citing articles. The user can specify the depth to which these articles are presented.

Figure 16: Citation Network

A further citation network example is presented in Figure 17.

Figure 17: Citation Network

For further information please contact Simon Kampa or the OpCit project.