Semantic annotation is one of the useful solutions to enrich target's (systems, models, meta-models, etc.) information. There are some papers which use semantic enrichment for different purposes (integration, composition, sharing and reuse, etc.) in several domains, but none of them provides a complete process of how to use semantic annotations. This paper identifies three main components of semantic annotation, gives a formal definition of semantic annotation method and presents a survey of current semantic annotation methods which include: languages and tools that can be used to develop ontology, the design of semantic annotation structure models and the corresponding applications. The survey presented in this paper will be the basis of our future research on models, semantics and architecture for systems interoperability.