Blogs are documents that have a fluid format, both in terms of content as well as design. There are several systems of classifying blogs. In A taxonomy of blogs (2008), blogs are categorized as pamphleteering, digest, advocacy, popular mechanics, exhibition, gatewater, diary, advertisement and news.
Many of these functions overlap, for example a blog could be a diary as well as exhibition blog. To me these functions are for a more sophisticated blogging culture, where many niches and sub-themes can exist.
For example, in politics, for Australia with its shadow government, liberal, left wing and right wing variants of political blogs can exist. In Malaysia, a division between government and opposition is probably enough so as not to confuse voters.
Wikipedia (2008) classifies blogs according to five categories, which are personal, corporate, genre, media type and device. These also can overlap in function. In terms of differentiation, the media type blogs stand apart from the rest due to their popularity and branding.
These include vlogs (video sharing) and photoblogs (photo sharing). Personal microblogs such as Twitter also stand out due to the ability to record specific moments in time.
Wikipedia 2009, Blog, wikipedia.org, viewed 17 November 2009 http://en.wikipedia.org/wiki/Blog
The Media Report, 2008, A taxonomy of blogs, www.abc.net.au, viewed 17 November 2009 http://www.abc.net.au/rn/mediareport/stories/2008/2372882.htm#transcript)