Syntax-Directed Translation Schemes (SDTS): Integrating Semantics into Parsing

Explore Syntax-Directed Translation Schemes (SDTS), a method for embedding semantic actions directly into grammar rules during compiler design. This guide explains how SDTS combines grammar and code execution for efficient source-to-machine code translation.

Syntax-Directed Translation Schemes (SDTS)

What is a Syntax-Directed Translation Scheme?

A Syntax-Directed Translation Scheme (SDTS) is a formal mechanism used in compiler design to integrate semantic actions (code that performs operations on the program’s data) directly into the grammar rules. It combines the power of context-free grammars for describing the structure of a programming language with the capability to execute code as part of the parsing process. This allows compilers to perform actions as the code is parsed, which enables more efficient translation from source code to machine code. The actions are typically embedded within the grammar’s production rules to specify precisely when they should occur.

How SDTS Works

In an SDTS, semantic rules (actions) are embedded within a context-free grammar’s production rules. The placement of an action within a production rule is typically indicated by enclosing the action in curly braces {}. The actions define the operations performed during the translation process, and their position within the grammar ensures they execute at the appropriate stage of parsing. This approach enhances efficiency by performing actions as part of the parsing process.

Example SDTS

Here's an example SDTS that evaluates arithmetic expressions. The semantic rules calculate the value of an expression.

E.VAL represents the value of the expression; I.VAL represents the integer value; and LEXVAL represents the value of the digit token.