Knowledge Graph to Text

Knowledge graph to text is the NLP task of generating natural language from knowledge graph structures — converting entities, relationships, and triples (subject-predicate-object) stored in knowledge graphs into fluent, coherent text that expresses the same information in human-readable form.

What Is Knowledge Graph to Text?

• Definition: Generating natural language from knowledge graph data.
• Input: KG triples (entity-relation-entity), subgraphs, or paths.
• Output: Fluent text expressing the graph information.
• Goal: Verbalize structured knowledge into readable narratives.

Why KG-to-Text?

• Accessibility: Knowledge graphs are for machines — text is for humans.
• Dialogue Systems: Generate informative responses from KG backends.
• Content Creation: Auto-generate descriptions from knowledge bases.
• Data Augmentation: Create training data from KGs for NLP tasks.
• Question Answering: Verbalize KG query results as natural answers.
• Education: Explain KG contents to non-technical users.

Knowledge Graph Basics

Triples:
- Format: (Subject, Predicate, Object).
- Example: (Albert_Einstein, birthPlace, Ulm).
- Example: (Ulm, country, Germany).

Subgraphs:
- Connected set of triples about an entity or topic.
- Example: All triples about Albert Einstein.

Knowledge Graphs:
- Wikidata: General knowledge (100M+ items).
- DBpedia: Structured data from Wikipedia.
- Freebase: Google's knowledge graph (deprecated, data available).
- Domain KGs: Medical (UMLS), biomedical (DrugBank), scientific.

KG-to-Text Approaches

Template-Based:
- Method: Pre-defined sentence templates for each relation type.
- Example: "[Subject] was born in [Object]" for birthPlace relation.
- Benefit: Guaranteed accuracy and grammaticality.
- Limitation: Limited to known relation types, repetitive output.

Neural Generation:
- Method: Encode graph structure, decode to text.
- Graph Encoding: GNN, graph transformers, or linearized triples.
- Decoder: Autoregressive language model.
- Benefit: Natural, varied text generation.

LLM-Based:
- Method: Provide triples in prompt, generate text.
- Format: List triples or structured representation in prompt.
- Benefit: Strong generation quality without fine-tuning.
- Challenge: May add information not in input triples.

Graph Encoding Methods

Linearization:
- Convert triples to text: "Subject | Predicate | Object."
- Concatenate all triples with separators.
- Simple but loses graph structure.

Graph Neural Networks:
- Encode entities as nodes, relations as edges.
- Message passing captures structural information.
- Output node/graph embeddings for decoder.

Graph Transformers:
- Self-attention over graph nodes with structure-aware attention masks.
- Capture both local (neighbors) and global (distant) relationships.
- State-of-the-art for many KG-to-text benchmarks.

Challenges

• Faithfulness: Only express information present in input triples.
• Aggregation: Combine multiple triples into coherent sentences.
• Ordering: Determine natural order to present information.
• Referring Expressions: Use pronouns and references naturally.
• Complex Relations: Multi-hop paths and nested relationships.
• Rare Entities: Handle unseen entities and relations.

Evaluation

• BLEU/METEOR/ROUGE: Surface text similarity metrics.
• BERTScore: Semantic similarity using contextual embeddings.
• Faithfulness: Check all triples are expressed, none fabricated.
• Human Evaluation: Fluency, adequacy, grammaticality.

Key Datasets

• WebNLG: DBpedia triples → text (15 categories, widely used).
• AGENDA: Scientific KG → paper abstracts.
• GenWiki: Wikidata triples → Wikipedia sentences.
• TEKGEN: Large-scale Wikidata → text.
• EventNarrative: Event KG → narratives.

Applications

• Virtual Assistants: Verbalize KG query results naturally.
• Wikipedia Generation: Auto-generate articles from Wikidata.
• Healthcare: Verbalize patient knowledge graphs for clinicians.
• E-Commerce: Generate product descriptions from product KGs.
• Education: Explain concepts from educational knowledge graphs.

Tools & Models

• Models: T5, BART, GPT-4 for generation; GAT, GCN for encoding.
• Frameworks: PyG (PyTorch Geometric) for graph encoding.
• Datasets: WebNLG Challenge for standardized evaluation.
• KG Tools: Neo4j, RDFLib, SPARQL for KG querying.

Knowledge graph to text is essential for making structured knowledge human-accessible — it bridges the gap between machine-readable knowledge representations and human-readable text, enabling knowledge graphs to serve not just algorithms but people.