  Given that semantic Web realization is based on the critical mass of metadata
accessibility and the representation of data with formal knowledge, it needs to
generate metadata that is specific, easy to understand and well-defined.
However, semantic annotation of the web documents is the successful way to make
the Semantic Web vision a reality. This paper introduces the Semantic Web and
its vision (stack layers) with regard to some concept definitions that helps
the understanding of semantic annotation. Additionally, this paper introduces
the semantic annotation categories, tools, domains and models.
