So-called "breadcrumbs" (as defined in "Designing Web Usability" by Jakob Nielsen) are a feature of webpages that allow the user to see logical context and navigate. Breadcrumbs are really an ancestor path - a list of parent, grandparent, etc. showing the logical subtree in which the current page lives. Decorating all the pages of a website correctly and consistently is a tricky and boring task. Furthermore, the overall tree logically implicit in the paths may not be shown explicitly, even though such an overview might be valuable as a sitemap or table of contents.

All the information necessary for breadcrumb processing can be represented as a single tree structure. The main purpose of TreeDec is to allow website authors and designers to maintain the logical tree structure of their website in a single file and to use that file to control the systematic addition of breadcrumbs to the webpages of the site.

It should be emphasized that the logical organization of the pages of a website into a tree is independent of other organizational structures, in particular:

• The directory structure: the physical location of files may mirror the logical structure, but it need not do so. In general, physical location matters only to the developer, not to the end-user of the site.
• The link structure of a website is determined by the static links from one page to another. Several systems exist which detect and manipulate this structure (see Analyzing the Website). Note that the link structure typically is not hierarchical, but rather a directed graph. TreeDec's GenTree utility program uses the link structure as a basis for creating a tree.
• The chronological context is simply the sequence of pages recently visited by the user; it is typically the basis for a browser's BACK button and/or its history feature. The "breadcrumb" metaphor more properly applies to this context than to the ancestor path of a logical tree.

Finally, if the location of a webpage in the logical tree is important, then perhaps the user would want to see not only ancestors, but other nearby nodes, namely siblings and children. Thus the user can go anywhere within the immediate vicinity of the current page. Since this information is implicit in the tree structure anyway, sibling and child links are available as options.

For a more detailed overview of TreeDec, see this article.

The TreeDec system includes pre-processing utility programs called td-convert-ll and GenTree to help the website developer create a file representing the tree structure. TreeDec itself accepts as input the tree file (however created) and applies it to the website. The result is a consistent labelling of all the webpages, plus an HTML skeleton of the hierarchy to be used as a table of contents. Here is an example of the output of TreeDec: the root page and table of contents of a geography oriented decorated website (with no actual content).

See NIST Web Metrics disclaimer.