Definition
A prefix-tree data structure used in AI to optimize token-level searching and enforce constrained decoding by mapping valid sequences, ensuring an LLM only generates outputs that match a predefined schema or vocabulary. It trades high memory consumption for O(L) lookup time, where L is the sequence length, providing a deterministic path for token selection.
In AI agents, this is not a general search index but a structural constraint used to prune invalid next-token candidates during inference.
"A predictive texting keyboard that only highlights the next possible letters based on a dictionary, graying out all invalid keys."
- Constrained Decoding(Primary Use Case)
- Tokenization(Prerequisite)
- Logits Processor(Component)
- Finite State Machine (FSM)(Alternative Implementation)
Conceptual Overview
A prefix-tree data structure used in AI to optimize token-level searching and enforce constrained decoding by mapping valid sequences, ensuring an LLM only generates outputs that match a predefined schema or vocabulary. It trades high memory consumption for O(L) lookup time, where L is the sequence length, providing a deterministic path for token selection.
Disambiguation
In AI agents, this is not a general search index but a structural constraint used to prune invalid next-token candidates during inference.
Visual Analog
A predictive texting keyboard that only highlights the next possible letters based on a dictionary, graying out all invalid keys.