Which statements about SDD1 and SDD2 are correct in GATE CS 2026 Q22?

Options A and B are correct. SDD2 is S-attributed with only synthesized attributes (A). Both SDDs generate the same language of type declarations (B). Option C is incorrect — SDD1 is L-attributed but contains both synthesized attributes (T.type, D.type) and an inherited attribute (V.type), not only inherited attributes.

What is an S-attributed SDD?

An S-attributed SDD (Synthesized-attributed) contains only synthesized attributes. All attribute values are computed from the children of a node or from the node itself, flowing upward in the parse tree. S-attributed SDDs are always L-attributed as well.

What is an L-attributed SDD?

An L-attributed SDD allows both synthesized attributes and inherited attributes, as long as each inherited attribute of a symbol on the right-hand side depends only on attributes of symbols to its left in the production or on inherited attributes of the head (parent) symbol.

In SDD1, what type of attribute is V.type?

In SDD1, V.type is an inherited attribute. It is passed down from the parent production D → TV, where V.type receives the value of T.type. This makes V.type an inherited attribute flowing from parent to child.

SDD1 vs SDD2: S-Attributed L-Attributed Syntax Directed Definitions

Computer Sciences > GATE 2026 SET-1 > Syntax Directed Definitions

Consider the following two syntax-directed definitions SDD1 and SDD2 for type declarations.

𝐷 is the start symbol, and 𝑖𝑛𝑡, 𝑓𝑙𝑜𝑎𝑡 and 𝑖𝑑 are the three terminals. The non-terminal 𝑉1 is the same as 𝑉 and the non-terminal 𝐷1 is the same as 𝐷. Here, the subscript is used to differentiate the grammar symbols on the two sides of a production. The function 𝑝𝑢𝑡 updates the symbol table with the type information for an identifier. Let P and Q be the languages specified by grammars G1 and G2, respectively. Which of the following statements is/are true?

SDD2 is an S-attributed SDD and contains only synthesized attributes.

The languages P and Q are the same

SDD1 is an L-attributed SDD and contains only inherited attributes.

The specification of SDD1 and SDD2 are such that the same entries get added to the symbol table.

Correct : a,b

Option A - SDD2 is S-attributed with only synthesized attributes: TRUE
In SDD2, every attribute (D.type, T.type) is computed from the children and flows upward. There are no inherited attributes. This makes SDD2 a classic S-attributed SDD.
Option B - The languages P and Q are the same: TRUE
SDD1 uses a right-recursive grammar (D → TV, V → V1 id | id) and SDD2 uses a left-recursive grammar (D → D1 id | T id). Both describe declarations of the form "type id1, id2, ..." - the same language, just with different parse tree structures.
Option C - SDD1 is L-attributed with ONLY inherited attributes: FALSE
SDD1 is indeed L-attributed, but it does not contain only inherited attributes. T.type and D.type are synthesized attributes. Only V.type is inherited (it receives T.type from the parent). So the claim of "only inherited" is incorrect.
Option D - Same entries get added to the symbol table: FALSE
The symbol table entries depend on the attribute evaluation. Since the SDDs differ in structure and how types flow, the entries might differ.

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