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The Alto parser

Welcome to Alto, the Algebraic Language Toolkit.

Alto is a parser and decoder for Interpreted Regular Tree Grammars (IRTGs). Its main features are:

Represents grammars from a wide variety of popular grammar formalisms as IRTGs, including:
- Context-free grammars
- Tree-adjoining grammars (TAG)
- Tree automata and bottom-up tree transducers
- Synchronous context-free grammars, TAG, etc.
- Tree-to-string and string-to-tree transducers
- Synchronous Hyperedge Replacement Grammars (HRG): Alto is the fastest published HRG parser in the world
- and many more
Implements chart-based algorithms for
- parsing
- synchronous parsing (with inputs from multiple sides of a synchronous grammar)
- decoding (to another side of a synchronous grammar)
- maximum likelihood and expectation maximization (EM) training
- binarization
Supports weighted/PFCG-style and log-linear probability models for all of these grammar formalisms.
Built for easy extensibility: implement your own grammar formalism by adding an Algebra class, and use any of the Alto algorithms directly.
Comes with a GUI that provides access to most of these algorithms and visualizes parsing results.

The basic theory of IRTGs is explained in Koller & Kuhlmann, IWPT 2011. You can find more details on the Literature page.

Alto is implemented in Java and can be downloaded here.