Mirroring a Pan-Crystallography Server

The IUCr Executive Committee approved in 1996 the establishment of a pan-crystallography server, combining the functions of the existing IUCr web services, the Crystallography World Wide pages maintained in Geneva, and the SINCRIS software pages maintained in Paris, together with future contributors of large collections of other crystallographic information. The complete set of information services was to be mirrored at appropriate sites worldwide, to provide convenient access to the most suitable network access points.

The project is more complex than the straightforward mirroring of static files or html pages, since the IUCr information services include access to databases that should not be mirrored, for technical reasons or on grounds of confidentiality. The following working proposals have been adopted for the initial implementation of the pan-crystallography system.

• Each major contributor to the project shall make available a set of html pages and ancillary files as the sole contents of a single directory or a hierarchy of directories with a single root.
• Mirror sites must be able to present the various root directories of these contributions as top-level nodes from a public http server. That is, the IUCr web pages should be visible from the URL
  http://mirror.site.name/iucr-top/
  while the Crystallography World Wide pages should be visible from the URL
  http://mirror.site.name/cww-top/
  The purpose of this is twofold:
  • URLs are identical across all mirror sites with the exception of the server host name.
  • Links within the directory hierarchy can be maintained within a known naming structure. This is important because the IUCr directory hierarchy can run very deep, and the maintenance of correct relative URL's of the form <IMG SRC="../../../../../../../icons/icon.gif"> becomes very difficult. Reference to a standard root directory on each host makes it much easier to maintain correct links of the form <IMG SRC="/iucr-top/icons/icon.gif">, while ensuring that all such links are served by the same host.
  The administrator of the mirror site may introduce top-level nodes to his web server either by making symbolic links from the top of the pan-crystallography directory trees, or by adding their locations as aliases in the appropriate httpd configuration files.
• The http server should be configured to serve a file of name index.html as the index page for the directory in which it resides, so that a request for a directory is served with the corresponding index.html file.
• So far as is possible, each web page accessible on the pan-crystallography service should include at its top one or more icons, of size 85x35 pixels, identifying it as a component of the service, and acting as navigational hyperlinks to related pages within the service. While the various participants in the pan-crystallography scheme have a reasonable degree of freedom over their style of presentation of information, they are recommended to conform to a small set of stylistic guidelines to impose a certain house style across the entire service.