@article{mavrogiannis2023cook2ltl,
title={Cook2LTL: Translating Cooking Recipes to LTL Formulae using Large Language Models},
author={Angelos Mavrogiannis and Christoforos Mavrogiannis and Yiannis Aloimonos},
journal={arXiv preprint arXiv:2310.00163},
year={2023},
}
Overview
Cook2LTL is a system that receives a cooking recipe in natural language form, reduces high-level cooking actions to robot-executable primitive actions through the use of LLMs, and produces unambiguous task specifications written in the form of LTL formulae.
System Architecture
The input instruction $r_i$ is first preprocessed and then passed to the semantic parser, which extracts meaningful chunks corresponding to the categories $\mathcal{C}$ and constructs a function representation $\mathtt{a}$ for each detected action. If $\mathtt{a}$ is part of the action library $\mathbb{A}$, then the LTL translator infers the final LTL formula $\phi$. Otherwise, the action is reduced to a lower-level of admissible actions ${a_1,a_2,\dots a_k}$ from $\mathcal{A}$, saving the reduction policy to $\mathbb{A}$ for future use. The LTL translator yields the final LTL formulae from the derived actions.
Named Entity Recognition
The first step of Cook2LTL is a semantic parser that extracts salient categories towards building a function representation $\mathtt{a}=\mathtt{Verb(What?,Where?,How?,Time,Temperature)}$ for every detected action. To this end, we annotate a subset (100 recipes) of the Recipe1M+ dataset and fine-tune a pre-trained spaCy NER BERT model to predict these categories in unseen recipes at inference. To annotate the recipes we used the Brat annotation tool (installation instructions). To fill in context-implicit parts of speech (POSs), we use ChatGPT or manually inject them into the sentence. The resulting edited recipes can be found in the edited_recipes.csv file. The code to train the NER model is in train_ner.py.
Reduction to Primitive Actions
Action Reduction
If $\mathtt{a}\notin\mathcal{A}$, we prompt an LLM with a pythonic import of the set of admissible primitive actions $\mathcal{A}$ in the environment of our use case, two example function implementations using actions from this set, and the function representation $\mathtt{a}$ in the form of the pythonic function along with its parameters. This is implemented in the action_reduction function by calling gpt-3.5-turbo through the OpenAI API. The new action is added to the pythonic import, enabling the system to invoke it in future action reductions.
Note: An OpenAI API key is required for. You can create an account and set up API access here.
Action Library
Every time that we query the LLM for action reduction, we cache $\mathtt{a}$ and its action reduction policy (in the cache_action function) to an action library $\mathbb{A}$ for future use through a dictionary lookup manner. At runtime, a new action $\mathtt{a}$ is now checked against both $\mathcal{A}$ and $\mathbb{A}$. If $\mathtt{a}\in\mathbb{A}$, which means that $\mathtt{Verb}$ from $\mathtt{a}$ matches the $\mathtt{Verb}$ from an action $\mathtt{a}_\mathbb{A}$ in $\mathbb{A}$ and the parameter types match (e.g. both actions have $\mathtt{What?}$ and $\mathtt{Where?}$ as parameters), then $\mathtt{a}$ is replaced by $\mathtt{a}_\mathbb{A}$ (reuse_cached_action function) and its LLM-derived sub-action policy, and passed to the subsequent LTL Translation step.
Note: A new action library is initialized at runtime but the user can also load and build upon an existing action library (load_action_library function).
LTL Translation
We assume the following specification pattern for executing a set of implicitly sequential actions ${\mathtt{a}_1,\mathtt{a}_2,\dots,\mathtt{a}_n}$ found in a recipe instruction step:
$$\mathcal{F}(\mathtt{a}_1\wedge \mathcal{F}(\mathtt{a}_2\wedge\dots\mathcal{F}\mathtt{a}_n)))$$ The parse_chunks function scans every chunk extracted from the NER module for instances of conjunction, disjunction, or negation, and produces an initial LTL formula $\phi$ using the above equation and the operators $\mathcal{F},\wedge,\vee,\lnot$. Following the action reduction module, the decode_LTL function substitutes any reduced actions to the initial formula $\phi$. For example, if $\mathtt{a}\rightarrow{a_1,a_2,\dots,a_k}$, then $\mathcal{F}\mathtt{a}$ is converted to the formula $\mathcal{F}(a_1\wedge \mathcal{F}(a_2\wedge\dots\mathcal{F}a_n)))$. In cases where the $\mathtt{Time}$ parameter includes explicit sequencing language, the LLM has been prompted to return a $\mathtt{wait}$ function, which is then parsed into the ($\mathcal{U}$ : $\mathtt{until}$) operator and substituted in $\phi$.
