blojsom has the unique capability where you can map the default category as either a category itself or as an aggregator of a subset or all of the categories on your blog. The default category as defined in blojsom is the "/" category or the top-most category. Looking at it another way, if the URL to your blog is http://your.blog.com/blojsom/blog/john/, that last "/" in the URL is specifying to blojsom that it should retrieve the top-most category.

Aggregating all categories on your blog for the default category

The following screenshot from the administration console shows you what the default category mapping for the various flavors defined for blojsom when it is first installed.

In this scenario, since no categories are defined for the default category mapping, blojsom will aggregate entries from all your categories for any of the requested flavors.

Aggregating a subset of the categories on your blog for certain flavors for the default category

The following screenshot from the administration console shows a scenario where all requested flavors except for the RSS 2 flavor will show entries from the general, java, and osx categories if the request is made for the default category. If there is not an overriding set of categories for a particular flavor, blojsom will fallback to the blog default category mapping. For the RSS 2 flavor, blojsom will show entries from the general, osx, and music categories if the request is made for the default category.

Creating specific flavors for aggregating categories under a particular topic area

Finally, you can get creative and define specific flavors on your blog to aggregate categories, for example, falling under a particular topic area. In the following screenshot from the administration console, a macintosh flavor is defined, let's say it uses the HTML template, where the osx, netnewswire, pulpfiction, and expose categories are aggregated for the default category.