SMW as Lego blocks
Wordpress is like Barbie's Kitchen. You get a kit that lets you do what it shows on the box... blogs, RSS feeds, blog management, with extensions you can create maps, events, and so on.
Semantic Mediawiki (SMW) is like Lego blocks. You can combine the basic blocks to make just about any shape, with extensions you can create your own content types, special views and functions.
Wordpress is easier to use (except when it comes to quick hypertext editing, where wikis, after a quick introduction, rule). But with SMW, you can recreate most typical functions, and also recombine pieces. You can take the pieces of a "table" (a map location embedded in a page) and make a mosaic (a collection of map locations about a topic). The SMW approach is less rounded, but you can re-use the pieces and constantly build on your knowledge.
This is a characteristic of semantic sites. Each piece of content is well defined and re-usable. Also like Lego blocks, the design is obvious, transparent and open (in SMW, using Special:Version and change histories).
Wordpress supports some semantic features now, but I prefer the "Lego" approach, where people can more easily create different components, without resorting to a complex and difficult to maintain low level language.
There is more and more re-usable content and components on the Web; MIT's SIMILE project was created to make it easy to embed interactive views across sites and is supported by SMW and Wordpress, Microformats and RDFa make it possible to aggregate content in one place, whether it's restaurant reviews or departmental budgets.
SMW can support these functions for any site user, in a culture of transparently exchanging knowledge, but users have to learn the markup, which at times is not easy. A SMW site is best represented by a collection of people, some of whom are expert helpers.
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