Mentioned under hardliners (some parts of which could be incorporated here).
In linguistics, formal semantics is the business of modeling the meaning of utterances in terms of lower-level units; for example, modeling the meaning of sentences in terms of the meanings of their words. "Formal" means that the models should ideally be rigorous and mathematical.
A complete formal semantics for a language would have to model both individual word meanings (or morphemes, or some other low-level unit) and the language's compositional semantics, which is how bigger meanings are built up out of the small ones. In practice, I get the impression that linguists in this area largely concentrate on the compositional semantics. But it's a big biz in linguistics, and I'm sure there are all kinds.
A complete formal semantics is far beyond the state of the art for any natural language. I also happen to believe that it is far beyond the state of the art for Lojban. If it can be done at all with current knowledge, I think it would be necessary to design a new language starting from scratch for the purpose. On the other hand, partial semantic models can still be cool. The book provides some, here and there, and we may be able to discover or retrofit others into Lojban. But I also believe that too much bending and cutting to retrofit a formal semantic model, no matter how cool, would risk breaking the language. mi'e jezrax