Semantics reveals the meaning of syntactically valid strings in a language
It describes the behavior that a computer follows when executing a program in the language
This behaviour might be disclosed by describing the relationship between the input and output of a program or by a step-by-step explanation of how a program executes on a real or an abstract machine
It has links with other areas of computer science such as programming language design, type theory, compilers and interpreters, program verification and model checking
A semantic error might be required to be spotted by the programmer
An example of semantic error can be usage of an uninitialised variable, which might not be easily detected during parsing
During Semantic analysis, the compiler adds semantic information to the parse tree and builds the symbol table
This phase performs semantic checks such as
Semantic analysis usually requires a complete parse tree, meaning that this phase logically follows the parsing phase, and logically precedes the code generation phase, though it is often possible to fold multiple phases into one pass over the code in a compiler implementation
