Complexity-research.org makes use of the an open source content management software: http://www.drupal.org. This software creates multiple access paths for each contribution, via the menu structure and via an URL.
In essence, every page of the site is a node with a unique Node ID (NID) and can always be accessed via complexity-research.org/node/NID. Besides that, one or more URL aliases are automatically created for each node to allow browsing for it by title and its placement in the book hiearchy, the list of events, list of users, and so on. You control the URL alias by choosing the content type and the title of your page. Automatically created links on the web site normally use these intuitive aliases rather then node/NID.
An URL alias can change, for example because a user changes his or her username, or because the title of a top level book page is changed. In that case the automatically created links are updated. But static links that you manually inserted into your pages, or that you used on other domains, are not automatically changed. Unless you are sure that the URL alias will never change you should therefor use the node/NID for static links. You can always learn the NID of a page by hovering over or clicking on the edit button at the top of that page. This will refer you to a new page with URL node/NID/edit.
