Dear Kun,
I am very sorry that it took me so long to answer.
As I remember, when we began working on the schema, we discussed a possibility of using @next and @prev for connecting posts. As far as I know, these attributes are typically used to connect the parts of one complete text, which for some reasons was divided in parts. For example, the pieces of an article in a newspaper: the beginning of an article is on the front page and the end on page 16. In this case I connect them by using @next and @prev. Another typical case of using these attributes is a footnote, which begins on one page and ends on another. So @prev and @next are rather connecting two, three or more parts of one unit, than connecting related texts. As we considered posts as individual, more or less independent texts, which have separate authors, we didn't chose global linking attributes as @prev and @next for connecting them. But I think, that the notion of @ref should also be discussed again, because the semantic of it in TEI is also different from what we need in our case. @ref provides a full definition of a certain entity. I think, that we could put the case of these attributes on a discussion.