A Survey on Recent Advances in LLM-Based Multi-turn Dialogue Systems

In plain words

Chatbots that must remember what was said several turns earlier are harder to build than one-question systems. This survey looks at how large language models (LLMs) are used for that job. It has two kinds of chatbot in view: bots that finish a specific task, such as booking a hotel, and bots that just chat about anything.

The authors first explain the models and the common ways to adapt them, such as training only a small add-on or writing better prompts. They then go through the task-bot and chat-bot designs, the ways of scoring them, and the datasets used to test them. It ends with open problems: cost, memory over long conversations, robustness in new domains, tool use and privacy. It is a map of the field, not a new system to run.

TL;DR

• A survey, not a method: it sets out LLM architectures, adaptation methods, task-oriented (TOD) and open-domain (ODD) dialogue systems, metrics and datasets §1 fig. 1.
• It runs no experiments of its own. Its tables list methods and dataset statistics taken from the cited papers tab. 2 tab. 3 tab. 4 tab. 5.
• Its main takeaways are the open problems in §7: compute cost, long-context consistency, domain robustness, tool use and privacy §7.
• Several details in the text are unclear or wrong, including a mislabelled model row, a citation that points to the wrong paper and a pair of equations with undefined terms. See "Pitfalls" before relying on any table.
• No official code. Nothing here can be implemented as one algorithm.

Problem

The survey starts from a sequence-to-sequence view of dialogue: the system maps the user's turns and its own earlier turns to the next response §1. Multi-turn systems must keep track of long-range context, stay consistent and handle ambiguity §1. Earlier reviews are said to cover either non-LLM systems or only one kind of system; the authors position their survey as covering both TOD and ODD with LLMs §1.

The paper does not state a quantitative problem or a benchmark gap. Its scope is qualitative: a review of methods, metrics and datasets, plus a list of open problems §1 §7.

Method

Scope and structure. The survey has four parts: LLM architectures and adaptation methods §2; LLM-based TOD systems §3; LLM-based ODD systems §4; metrics and datasets §5 §6. Section 7 discusses open problems. The organisation is shown in a diagram fig. 1.

LLM families by Transformer type §2 tab. 1. Models are grouped as decoder-only (causal or prefix masking), encoder-only and encoder-decoder. Causal decoders use unidirectional attention, so each token attends only to earlier tokens and itself §2.1.1. Prefix decoders allow bidirectional attention over the prefix and unidirectional attention over generated tokens §2.1.2. The survey lists GPT, LLaMA and ChatGLM as decoders, BERT and UNILM as encoders and T5 and BART as encoder-decoders §2.1 §2.2 §2.3 tab. 1.

Adaptation methods §2.4 §2.5.

1. Full fine-tuning updates all parameters of a pre-trained model on a dataset D to minimise a task loss eq. 1 §2.4.1.
2. Adapters insert a down-projection, a non-linearity and an up-projection, with a residual connection, into the layers. Only the adapter parameters are trained eq. 2 eq. 3 eq. 4 §2.4.2.
3. LoRA adds a low-rank update ΔW = BA to a frozen weight matrix W, with B of shape m × r and A of shape r × n and r much smaller than m and n eq. 5 eq. 6 §2.4.2. QLoRA combines LoRA with 4-bit quantisation of the base model §2.4.2.
4. Instruction fine-tuning trains on instruction, input and output triples §2.4.2.
5. Stability methods: R3F and R4F add a regularisation term to the task loss, and R4F also adds a reparameterisation term eq. 7 eq. 8 §2.4.3. SMART and FreeLB use adversarial perturbations of the input or the word embeddings with a penalty weight ρ eq. 9 eq. 10 §2.4.3.
6. Prompting without weight changes: in-context learning §2.5.1, chain of thought (zero-shot with "Let's think step by step", or least-to-most decomposition) §2.5.2, and retrieval-augmented generation in three stages, naive, advanced (pre- and post-retrieval steps) and modular §2.5.3.

Task-oriented systems §3 tab. 2.

Pipeline-based systems have four modules: NLU (intent and slot extraction), dialogue state tracking (DST), policy learning (PL) and NLG. DST and PL together form the dialogue manager §3.1 fig. 2. The table lists one or more LLM-era methods for each module tab. 2. End-to-end systems map user input to a response in one model: fully end-to-end systems train one model on all sub-tasks, and modular end-to-end systems keep module boundaries inside a pre-trained model §3.2 fig. 3.

# Pipeline-based TOD, one user turn  [§3.1]
# Input:  user utterance, dialogue history, previous state
# Output: system response, updated state

def pipeline_turn(utterance, history, state):
    # NLU: intent and slot values from this turn  [§3.1]
    intent, slots = nlu(utterance, history)

    # DST: update the belief state  [§3.1]
    state = track_dialogue_state(state, intent, slots, history)

    # PL: choose the next dialogue action  [§3.1]
    action = policy(state)

    # NLG: turn the action into text  [§3.1]
    response = nlg(action)
    return response, state

Open-domain systems §4 tab. 3. Three families are given: retrieval-based (select an existing response from candidates), generation-based (write a response, with knowledge or personalisation added) and hybrid (combine retrieval and generation) §4.1 §4.2 §4.3. The table lists 21 methods across the three families tab. 3.

Evaluation §5. Automatic TOD metrics: joint goal accuracy eq. 24, slot accuracy eq. 25, average goal accuracy eq. 26, requested-slot macro F1 eq. 27 eq. 28 eq. 29 eq. 30, BLEU, and entity F1 §5.1.1. Automatic ODD metrics: perplexity eq. 31, BLEU, DIST-n and recall@K eq. 32 §5.1.2. Human evaluation looks at diversity, creativity, grammar, faithfulness, coherence and consistency §5.2.

Datasets §6 tab. 4 tab. 5. TOD: MultiWOZ, RiSAWOZ, CrossWOZ, PersuasionForGood, WOZ 2.0 and Stanford Multi-Domain §6.1. ODD: PersonaChat, MMdialog, DailyDialog, Pchatbot, PersonalDialogue and Douban §6.2.

Hyperparameters

This is a survey. It runs no training or evaluation, so there are no settings of its own. The table lists the numeric values the text states about models and methods. Items marked "not stated" are not given anywhere in the survey.

Results

No new results. The survey does not benchmark any method and makes no author-reported claim of improvement. The values below are dataset statistics it tabulates from the original dataset papers §6.1 §6.2.

Task-oriented datasets tab. 4:

Open-domain datasets tab. 5:

Setup: the survey's tables. The figures are as given there and are not independently checked. Units and counts differ between the table and text for some rows (see Pitfalls).

Paper vs code

No official code. The survey has no code, and its source has no link to a repository for itself. Checks made: the LaTeX source and abstract (no project page or repository for the survey); the GitHub repository search API with two queries ("LLM multi-turn dialogue survey" and "multi-turn dialogue survey LLM"), which returned no repositories. Links to dataset repositories in tab. 4 and tab. 5 are dataset pages, not survey code, and are not used.

Pitfalls

• Table 1 mislabels a row. The row under "BART series" names the model as "BERT". The row describes an encoder-decoder with cross-attention, which matches BART and T5 but not BERT tab. 1.
• Architecture claims are unsourced. The attention type listed for GPT-3.5 and GPT-4 (sparse unidirectional; multi-query unidirectional) has no source in the text tab. 1 §2.1.1. Treat those cells as unverified.
• Wrong citation for the Transformer. Section 2.3 cites the T5 paper for "the traditional Transformer model". The Transformer itself is cited elsewhere to a different reference §2.3 §2.
• Shared citation for three models. GLM-130B, ChatGLM and ChatGLM-6B all cite the same reference, which the bibliography titles as the GLM-130B paper §2.1.2. The ChatGLM entries are not separately sourced.
• Naive RAG cites a query-rewriting paper. The naive RAG description cites a reference whose bibliography title is "Query Rewriting in Retrieval-Augmented Large Language Models" §2.5.3. The citation may not support the sentence.
• Likely BERT error in the text. The BERT paragraph says BERT's "autoregressive prediction limits its effectiveness", in the same paragraph that describes BERT's masked-language-model objective, which is not autoregressive §2.2.1. Read the BERT description with that in mind.
• Equation with an undefined variable. The Recall@K formula eq. 32 has an index x that is not defined. As written it returns 0 or 1 per query, while the prose describes a ratio over relevant items.
• Macro-F1 index mismatch. The per-class formulas use classes i = 1 to 2 eq. 27 eq. 28 eq. 29, but the macro average eq. 30 runs over r classes. r is not defined in the text §5.1.1.
• Odd entries in the ODD method table. The table lists ReProver and LeanDojo, which the text describes as retrieval-augmented theorem proving, under open-domain dialogue methods tab. 3. The text gives no reason for this.
• Pchatbot and PersonalDialogue counts use different units. The text calls Pchatbot's total "dialogue pairs" ("almost 200 million") and the table calls the same number "dialogues" §6.2 tab. 5. PersonalDialogue is "sessions" and "utterances" in the text §6.2 and "dialogues" in the table tab. 5.
• WOZ 2.0 counts differ in the text. The text says the source CamRest has 676 dialogues and that WOZ 2.0 "contains 1,200 dialogues" §6.1. The table agrees with 1,200 tab. 4. The text does not explain how the two relate.
• Uncited claim in the perplexity paragraph. The text says perplexity is used to help diagnose mental disorders. No source is given for that use §5.1.2.
• Section and table numbers are inferred. The survey is an ACM-format LaTeX source. Section numbers here follow the order of \section and \subsection in that source, and table and equation numbers follow the order of appearance. Verify against the rendered PDF before quoting a number in another document.
• Figures are described, not reproduced. Image files are not used here. Figure references in this card point to the survey's figure order.

Lineage

• Builds on: the Transformer §2 and the model families it lists (GPT, LLaMA, ChatGLM, BERT, BART, T5) §2.1 §2.2 §2.3. No paper cards in this wiki.
• Compared against: earlier surveys named in the introduction: Arora et al. (general dialogue frameworks), Chen et al. (TOD and ODD with deep learning), Ni et al. (LLM-based multi-turn systems) and Qin et al. (end-to-end LLM task-oriented dialogue) §1. No paper cards in this wiki.
• Related to the survey's own themes: the agent systems ChatDev and MetaGPT §7. No paper cards in this wiki.
• Superseded by: not stated in this wiki.