Straight-line grammar
A straight-line grammar (sometimes with "straight-line" in scare quotes,[1] also abbreviated as SLG) is a formal grammar that generates exactly one string.[2] Consequently, it does not branch (every non-terminal has only one associated production rule) nor loop (if non-terminal A appears in a derivation of B, then B does not appear in a derivation of A).[2]
SLGs are of interest in fields like Kolmogorov complexity, Lossless data compression, Structure discovery and Compressed data structures.
The problem of finding a context-free SLG of minimal size that generates a given string is called the smallest grammar problem.
Formal Definition
A context-free grammar G is an SLG if:
1. for every non-terminal N, there is at most one production rule that has N as its left-hand side, and
2. the directed graph G=<V,E>, defined by V being the set of non-terminals and (A,B) ∈ E whenever B appears at the right-hand side of a production rule for A, is acyclic.[3]
An SLG in Chomsky normal form is equivalent to a straight-line program.
A list of algorithms using SLGs
- The Sequitur algorithm constructs a straight-line grammar for a given string.
- The Lempel-Ziv-Welch algorithm creates a context-free grammar in a such deterministic way that it is necessary to store only the start rule of the generated grammar.
- Byte pair encoding
See also
- Grammar-based code
- Non-recursive grammar - a grammar that doesn't loop, but may branch; generating a finite rather than a singleton language
References
- ↑ http://www.almob.org/content/1/1/4
- 1 2 Florian Benz and Timo Kötzing, “An effective heuristic for the smallest grammar problem,” Proceeding of the fifteenth annual conference on Genetic and evolutionary computation conference - GECCO ’13, 2013. ISBN 978-1-4503-1963-8 doi:10.1145/2463372.2463441, p. 488
- ↑ Markus Lohrey; Sebastian Maneth; Manfred Schmidt-Schauß (2009). "Parameter Reduction in Grammar-Compressed Trees". Proc. FOSSACS (PDF). LNCS. 5504. Springer. pp. 212–226. Here: p.215, Sect.2