RDF2vec.org

About RDF2vec

RDF2vec is a tool for creating vector representations of RDF graphs. In essence, RDF2vec creates a numeric vector for each node in an RDF graph.

RDF2vec was developed by Petar Ristoski as a key contribution of his PhD thesis Exploiting Semantic Web Knowledge Graphs in Data Mining [Ristoski, 2019], which he defended in January 2018 at the Data and Web Science Group at the University of Mannheim, supervised by Heiko Paulheim. In 2019, he was awarded the SWSA Distinguished Dissertation Award for this outstanding contribution to the field.

RDF2vec was inspired by the word2vec approach [Mikolov et al., 2013] for representing words in a numeric vector space. word2vec takes as input a set of sentences, and trains a neural network using one of the two following variants: predict a word given its context words (continuous bag of words, or CBOW), or to predict the context words given a word (skip gram, or SG):

This approach can be applied to RDF graphs as well. In the original version presented at ISWC 2016 [Ristoski and Paulheim, 2016], random walks on the RDF graph are used to create sequences of RDF nodes, which are then used as input for the word2vec algorithm. It has been shown that such a representation can be utilized in many application scenarios, such as using knowledge graphs as background knowledge in data mining tasks, or for building content-based recommender systems [Ristoski et al., 2019].

Consider the following example graph:

From this graph, a set of random walks that could be extracted may look as follows:

Hamburg -> country -> Germany            -> leader     -> Angela_Merkel
Germany -> leader  -> Angela_Merkel      -> birthPlace -> Hamburg
Hamburg -> leader  -> Peter_Tschentscher -> residence  -> Hamburg

For those random walks, we consider each element (i.e., an entity or a predicate) as a word when running word2vec. As a result, we obtain vectors for eall entities (and all predicates) in the graph.

The resulting vectors have similar properties as word2vec embeddings. In particular, similar entities are closer in the vector space than dissimilar ones, which makes those representations ideal for learning patterns about those entities. In the example below, showing embeddings for DBpedia and Wikidata, countries and cities are grouped together, and European and Asian cities and countries form clusters:

The two figures above indicate that classes (in the example: countries and cities) can be separated well in the projected vector space, indicated by the dashed lines. [Zouaq and Martel, 2020] have compared the suitability for separating classes in a knowledge graph for different knowledge graph embedding methods. They have shown that RDF2vec is outperforming other embedding methods like TransE, TransH, TransD, ComplEx, and DistMult, in particular on smaller classes. On the task of entity classification, RDF2vec shows results which are competitive with more recent graph convolutional neural networks [Schlichtkrull et al., 2018].

RDF2vec has been tailored to RDF graphs by respecting the type of edges (i.e., the predicates). Related variants, like node2vec [Grover and Leskovec, 2016] or DeepWalk [Perozzi et al., 2014], are defined for graphs with just one type of edges. They create sequences of nodes, while RDF creates alternating sequences of entities and predicates.

This video by Petar Ristoski introduces the main ideas of RDF2vec:

Trans* etc. vs. RDF2vec

A lot of approaches have been proposed for link prediction in knowledge graphs, from classic approaches like TransE [Bordes et al., 2013] and RESCAL [Nickel et al. ,2011] to countless variants. The key difference is that those approaches are trained to optimize a loss function on link prediction, which yields a projection of similar entities closely together in the vector space as a by product. On the other hand, the capability to predict links is a by product in RDF2vec, in particular in variants like order-aware RDF2vec. A detailed comparison of the commonalities and differences of those families of approaches can be found in [Portisch et al., to appear]

Extensions and Variants

There are quite a few variants of RDF2vec which have been examined in the past.

Walking RDF and OWL pursues exactly the same idea as RDF2vec, and the two can be considered identical. It uses random walks and Skip Gram embeddings. The approach has been developed at the same time as RDF2vec. [Alsharani et al., 2017]
KG2vec pursues a similar idea as RDF2vec by first transforming the directed, labeled RDF graph into an undirected, unlabeled graph (using nodes for the relations) and then extracting walks from that transformed graph. [Wang et al., 2021] Although no direct comparison is available, we assume that the embeddings are comparable.
Wembedder is a simplified version of RDF2vec which uses the raw triples of a knowledge graph as input to the word2vec implementation, instead of random walks. It serves pre-computed vectors for Wikidata. [Nielsen, 2017]
KG2vec (not to be confused with the aforementioned approach also named KG2vec) follows the same idea of using triples as input to a Skip-Gram algorithm. [Soru et al., 2018]
Triple2Vec follows a similar idea of walk-based embedding generation, but embeds entire triples instead of nodes. [Fionda and Pirrò, 2020]

Initially, word2vec was created for natural language, which shows a bit of variety with respect to word ordering. In contrast, walks extracted from graphs are different.

Consider, for example, the case of creating embedding vectors for bread in sentences such as Tom ate bread yesterday morning and Yesterday morning, Tom ate bread. For walks extracted from graphs, however, it makes a difference whether a predicate appears before or after the entity at hand. Consider the example above, where all three entities in the middle (Angela_Merkel, Peter_Tschentscher, and Germany) share the same context items (i.e., Hamburg and leader). However, for the semantics of an entity, it makes a difference whether that entity is or has a leader.

RDF2vec_oa [Portisch and Paulheim, 2021] tackles this by using an order-aware variant of word2vec [Ling et al., 2015].

RDF2vec always generates embedding vectors for an entire knowledge graph. In many practical cases, however, we only need vectors for a small set of target entities. In such cases, generating vectors for an entire large graph like DBpedia would not be a practical solution.

RDF2vec Light is an alternative which can be used in such scenarios. It only creates random walks on a subset of the knowledge graph and can produce embedding vectors for a target subset of entities fast. In many cases, the results are competitive with those achieved with embeddings of the full graph. [Portisch et al., 2020] Details about the implementation are found here.
LODVec uses the same mechanism as RDF2vec Light, but creates sequences across different datasets by exploiting owl:sameAs links, and unifying classes and predicates by exploiting owl:equivalentClass and owl:equivalentProperty definitions. [Mountantonakis and Tzitzikas, 2021]

One area which has been undergone extensive research is the creation of walks for the RDF2vec algorithm. While the original implementation uses random walks, alternatives have been explored include:

The use of different heuristics for biasing the walks, e.g., prefering edges with more/less frequent predicates, prefering links to nodes with higher/lower PageRank, etc. An extensive study is available in [Cochez et al., 2017a].
Zhang et al. also propose a different weighting scheme based on Metropolis-Hastings random walks, which reduces the probability of transitioning to a node with high degree and aims at a more balanced distribution of nodes in the walks. [Zhang et al., 2022]
A similar approach is analyzed in [Al Taweel and Paulheim, 2020], where embeddings for DBpedia are trained with external edge weights derived from page transition probabilities in Wikipedia.
In [Vandewiele et al., 2020], we have analyzed different alternatives to using random walks, such as walk strategies with teleportation within communities. While random walks are usually a good choice, there are scenarios in which other walking strategies are superior.
In [Saeed and Prasanna, 2018], the identification of specific properties for groups of entities is discussed as a means to find task-specific edge weights.
Similarly, NESP computes semantic similarities between relations in order to create semantically coherent walks. Moreover, the approach foresees refining an existing embedding space by bringing more closely related entities closer together. [Chekol and Pirrò, 2020]
Mukherjee et al. [Mukherjee et al., 2019] also observe that biasing the walks with prior knowledge on relevant properties and classes for a domain can improve the results obtained with RDF2vec.
The ontowalk2vec approach [Gkotse, 2020] combines the random walk strategies of RDF2vec and node2vec, and trains a language model on the union of both walk sets.

Besides changing the walk creation itself, there are also approaches for incorporating additional information in the walks:

[Bachhofner et al., 2021] discuss the inclusion of metadata, such as provenance information, in the walks in order to improve the resulting embeddings.

RDF2vec relies on the word2vec embedding mechanism. However, other word embedding approaches have also been discussed. For example, KGlove adapts the GloVe algorithm [Pennington et al., 2014] for creating the embedding vectors [Cochez et al., 2017b].

While the original RDF2vec approach is agnostic to the type of knowledge encoded in RDF, it is also possible to extend the approach to specific types of datasets.

OWL2vec and its successor OWL2vec* is an extension of RDF2vec which is tailored towards OWL ontologies [Holter et al., 2019, Chen et al., 2020].
onto2vec pursues a similar strategy. It first materializes the ontology (see our comment on materialization below), then performs random walks and feeds them into word2vec. [Smaili et al., 2018]

To materialize or not to materialize? While it might look like a good idea to enrich the knowledge graph with implicit knowledge before training the embeddings, experimental results show that materializing implicit knowledge actually makes the resulting embedding worse, not better.

In [Iana and Paulheim, 2020], we have conducted a series of experiments training embeddings on DBpedia as is, vs. training embeddings on DBpedia with implicit knowledge materialized. In most settings, the results on downstream tasks get worse when adding implicit knowledge. Our hypothesis is that missing information in many knowledge graphs is not missing at random, but a signal of lesser importance, and that signal is canceled out by materialization. A similar observation was made by [Alsharani et al., 2017].

Applications

RDF2vec has been used in a variety of applications. In the following, we list a number of those, organized by different fields of applications.

Knowledge Graph Refinement

Knowledge Graph Refinement subsumes the usage of embeddings for adding additional information to a knowledge graph (e.g., link/relation or type prediction), to extend its schema/ontology, or the identification (and potentially: correction) of existing facts in the graph [Paulheim, 2017]. In most of the applications, RDF2vec embedding vectors are used as representations for training a machine learning classifier for the task at hand, e.g., a predictive model for entity types. Applications in this area include:

TIEmb is an approach for learning subsumption relations using RDF2vec embeddings. [Ristoski et al., 2017]
Kejriwal and Szekely discuss the use RDF2vec embeddings for entity type prediction in knowledge graphs. [Kejriwal and Szekely, 2017] Another approach in that direction is proposed by Sofronova et al., who contrast supervised and unsupervised methods for exploiting RDF2vec embeddings for type prediction. [Sofronova et al., 2020] Furthermore, the usage of RDF2vec for type prediction in knowledge graphs is discussed in [Weller, 2021] and [Jain et al., 2021]. [Cutrona et al., 2021] report that using RDF2vec embeddings for type prediction yields similarly scoring results as using BERT embeddings trained on the entities' textual abstracts.
GraphEmbeddings4DDI utilizes RDF2vec for predicting drug-drug interactions [Çelebi et al., 2018]. A similar system is introduced by Karim et al., using a complex LSTM on top of the entity embeddings generated with RDF2vec [Karim et al., 2019]. Since the drug-drug-interactions are modeled as relation in the knowledge graphs used for the experiments, this task is essentially a relation prediction task. [Zhang et al., 2022] also target the prediction of drug-drug-interaction and drug-target-interaction, using a combination of CNN and BiLSTM as a downstream prediction model.
Ammar and Celebi showcase the use of RDF2vec embeddings for the fact validation task at the 2019 edition of the Semantic Web Challenge. [Ammar and Celebi, 2019]. A similar approach is pursued by Pister and Atemezing [Pister and Atemezing, 2019].
Chen et al. show that RDF2vec embeddings can be used for relation prediction and yields results competitive with TransE and DistMult [Chen et al., 2020].
Yao and Barbosa combines RDF2vec and outlier detection for detecting wrong type assertions in knowledge graphs [Yao and Barbosa, 2021].
Egami et al. utilize RDF2vec for clustering activities in a knowledge graph of daily living activities, and discuss the use of those clusters for refining the underlying ontology. [Egami et al., 2021]

Knowledge Matching and Integration

In knowledge matching and integration, entity embedding vectors are mostly utilized to determine whether two entities in two datasets are similar enough to each other to merge them into one. Different approaches have been proposed using RDF2vec for matching and integratino both on the schema as well as on the instance level:

MERGILO is a tool for merging structured knowledge extracted from text. A refinement of MERGILO using RDF2vec embeddings on FrameNet is discussed in [Alam et al., 2017].
EARL is a named entity linking tool which uses pre-trained RDF2vec embeddings. [Dubey et al., 2018]
ALOD2vec Matcher is an ontology matching system which uses pre-trained embeddings on the WebIsALOD knowledge graph to determine the similarity of two concepts. [Portisch and Paulheim, 2018]. The approach has later been extended to DBpedia, WordNet, Wikidata, Wiktionary, and BabelNet in [Portisch et al., 2021]. A similar approach is pursued by the DESKMatcher system, which uses domain specific embeddings from the business domain, e.g., the FIBO ontology [Monych et al., 2020].
AnyGraphMatcher is another ontology matching system which leverages RDF2vec embeddings trained on the two input ontologies to match [Lütke, 2019].
Azmy et al. use RDF2vec for entity matching across knowledge graphs, and show a large-scale study for matching DBpedia and Wikidata [Azmy et al., 2019]. A similar approach is introduced by Aghaei and Fensel, who combine RDF2vec embeddings with clustering and BERT sentence embeddings to identify related entities in two knowledge graphs [Aghaei and Fensel, 2021].
DELV is an entity matching approach for matching multiple knowledge graphs built on top of RDF2vec. It first embeds a central knowledge graph using RDF2vec, and then performs an RDF2vec embedding of satellite knowledge graphs with a slightly modified word2vec loss function, taking the minimization of the distance of already matched anchors into account.[Ruppen, 2018].
In a showcase for the MELT ontology matching framework, Hertling et al. show that by learning a non-linear mapping between RDF2vec embeddings of different ontologies, ontology matching can be performed at least for structurally similar ontologies [Hertling et al., 2020]. This is particularly remarkable since that metric measures similarity, not relatedness, which is actually needed for the task at hand.

Applications in NLP

In natural language processing, knowledge graph embeddings are particularly handy in setups that already exploit knowledge graphs, for example, for linking entities in text to a knowledge graph using named entitiy linking and named entity disambiguation. Applications of RDF2vec in the NLP field include:

TREC CAR is a benchmark for complex answer retrieval. The authors use pre-trained RDF2vec embeddings as one means to represent queries and answers, and for matching them onto each other. [Nanni et al., 2017a]
Inan and Dikenelli demonstrate the usage of RDF2vec embeddings in named entity disambiguation in the entity disambiguation frameworks DoSeR and AGDISTIS. [Inan and Dikenelli, 2017]
In a later work, Inan and Dikelli propose the use of RDF2vec embeddings together with a BiLSTM and a CRF layer for entity disambiguation. [Inan and Dikenelli, 2018]
Wang et al. have used RDF2vec embeddings for analyzing entity co-occurence in tweets [Wang et al., 2017].
Nanni et al. showcase the use of RDF2vec embeddings for entity aspect linking in [Nanni et al., 2018].
Nizzoli et al. use RDF2vec, among other features, to perform named entity linking of geographic entities, in particular for scoring candidates. [Nizzoli et al., 2020]
KGA-CGM is a system for describing images with captions. It uses RDF2vec embeddings for handling out-of-training entities [Mogadala et al., 2018].
Türker discusses the use of RDF2vec for text categorization by embedding both texts and categories [Türker, 2019].
Vakulenko demonstrates the use of RDF2vec in dialogue systems [Vakulenko, 2019].
G-Rex is a tool for relation extraction from text which leverages RDF2vec entity embeddings [Ristoski et al., 2020].
El Vaigh et al. show that using cosine similarity in the RDF2vec space creates a strong baseline for collective entity linking [El Vaigh al., 2020]. This is particularly remarkable since that metric measures similarity, not relatedness, which is actually needed for the task at hand.
FinMatcher is a tool for named entity classification in the financial domain, developed for the FinSim-2 shared task. It uses pre-trained RDF2vec embeddings on WebIsALOD [Portisch et al., 2021]
[Eingleitner et al., 2021] use RDF2vec embeddings to provide semantic tags for news articles.

Information Retrieval

In information retrieval, similarity and relatedness of entities can be utilized to retrieve and/or rank results for queries for a given entity. Examples for the use of RDF2vec in the information retrieval field include:

Nanni et al. describe a system for harvesting event collections from Wikipedia, where RDF2vec is used internally for entity ranking. [Nanni et al., 2017b]
Ad Hoc Table Retrieval using Semantic Similarity describes the use of pre-trained RDF2vec embeddings for retrieving Wikipedia tables. [Zhang and Balog, 2018] In a later extension, they distinguish two kinds of retrieval tasks (using either keywords or tables as queries), and show that entity embeddings with RDF2vec can be used for both scenarios. [Zhang and Balog, 2021] Table annotation with RDF2vec is also discussed in [Cutrona et al., 2021] and [Shigarov et al., 2021].
Cyber-all-intel is an application in the computer security domain. It uses RDF2vec vectors for retrieving information on security alerts [Mittal et al., 2019].
The COVID-19 literature knowledge graph is a large citation network of CoViD-19 related scientific publications, derived from the CORD-19 dataset. In [Steenwinckel et al., 2020], the authors exploit RDF2vec embeddings on that graph for facilitating the retrieval of related articles, as well as for clustering the large body of literature.
In the context of the Data Set Knowledge Graph, the retrieval of similar datasets has been discussed as a use case for RDF2vec. [Färber and Lamprecht, 2021]
Kim et al. discuss the use of RDF2vec on top of knowledge graphs created using open information extraction from text, in particular for retrieving similar entities to support situation awareness in combat situations. [Kim et al., 2021]

Predictive Modeling

Predictive modeling was the original use case for which RDF2vec was developed. Here, external variables (which might be continuous or categorical) are predicted for a set of entities. By linking these entities to a knowledge graph, entity embeddings have been shown to be suitable representations for the downstream predictive modeling tools. Examples in this field include:

Hascoet et al. show how to use RDF2vec for image classification, especially for classes of images for which no training data is available, i.e., zero-shot-learning. [Hascoet et al., 2017]
evoKGsim* combines similarity metrics and genetic programming for predicting out-of-KG relations. The framework implements RDF2vec as one source of similarity metrics. [Sousa et al., 2021]
Biswas et al. discuss the use of RDF2vec as a signal for predicting infobox types in Wikipedia articles [Biswas et al., 2018].
Egami et al. show the use case of geospatial data analytics in urban spaces by constructing a geospatial knowledge graph and computing RDF2vec embeddings thereon [Egami et al., 2018].
Hees discusses the use of pre-trained RDF2vec models for predicting human associations of terms [Hees, 2018].
The utilization of RDF2vec for content-based recommender systems is discussed in [Saeed and Prasanna, 2018], [Ristoski et al., 2019], and [Voit and Paulheim, 2021]. [Palumbo et al., 2019] report that RDF2vec performs better in terms of recommending novel items than other competitors.
Jurgovsky demonstrates the use of RDF2vec for data augmentation on the task of credit card fraud detection [Jurgovsky, 2019].
Hoppe et al. demonstrate the use of RDF2vec embeddings on DBpedia for improving the classification of scientific articles [Hoppe et al., 2021].
[Nunes et al., 2021] show how graph embeddings on biomedical ontologies can be utilized for predicting drug-gene-interactions. They train classifiers such as random forests over the concatenated embedding vectors of the drugs and genes.
[Sousa et al., 2021] use embeddings on the Gene ontology for various predictive modeling tasks in the biomedical domain, including the prediction of proteins and the interaction of diseases and genes.
Wang et al. use embeddings, including RDF2vec, to assess the similarity of proteins in the Gene Ontology [Wang et al., 2022].

Other Applications

No matter how sophisticated your categorization schema is, you always end up with a category called "other" or "misc.". Here are examples for applications of RDF2vec in that category:

REMES is an entity summarization approach which uses RDF2vec to select a suitable subset of statements for describing an entity. [Gunaratna et al., 2017] Another work proposing the usage of RDF2vec for entity summarization is discussed in [Li et al., 2020].
Similar to that, Shi et al. propose an approach for extracting semantically coherent subgraphs from a knowledge graph, which uses RDF2vec as a measure for semantic distance to guarantee semantic coherence. [Shi et al., 2021]
Jurisch and Igler demonstrate that utilization of RDF2vec embeddings for detecting changes in ontologies in [Jurisch and Igler, 2018].

References

These are the core publications of RDF2vec:

Petar Ristoski, Heiko Paulheim: RDF2Vec: RDF Graph Embeddings for Data Mining. International Semantic Web Conference, 2016
Petar Ristoski, Jessica Rosati, Tommaso Di Noia, Renato De Leone, Heiko Paulheim: RDF2Vec: RDF Graph Embeddings and Their Applications. Semantic Web Journal 10(4), 2019

Further references used above:

Sareh Aghaei, Anna Fensel: Finding Similar Entities Across Knowledge Graphs. International Conference on Advances in Computer Science and Information Technology, 2021.
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Faisal Alshargi, Saeedeh Shekarpour, Tommaso Soru, Amit Sheth: Concept2vec: Metrics for Evaluating Quality of Embeddings for Ontological Concepts. Spring Symposium on Combining Machine Learning with Knowledge Engineering, 2019
Ahmad Al Taweel, Heiko Paulheim: Towards Exploiting Implicit Human Feedback for Improving RDF2vec Embeddings. Deep Learning for Knowledge Graphs Workshop, 2020
Ammar Ammar, Remzi Celebi: Fact Validation with Knowledge Graph Embeddings. International Semantic Web Conference, 2019
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Stefan Bachhofner, Peb Ruswono Aryan, Bernhard Krabina, Robert David: Embedding Metadata-Enriched Graphs. International Semantic Web Conference, Posters and Demos, 2021.
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Matthias Jurisch, Bodo Igler: RDF2Vec-based Classification of Ontology Alignment Changes. Workshop on Deep Learning for Knowledge Graphs and Semantic Technologies, 2018
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Enrico Palumbo, Alberto Buzio, Andrea Gaiardo, Giuseppe Rizzo, Raphael Troncy, Elena Baralis: Tinderbook: Fall in Love with Culture. Extended Semantic Web Conference, 2019.
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Maria Angela Pellegrino, Michael Cochez, Martina Garofalo, Petar Ristoski: A Configurable Evaluation Framework for Node Embedding Techniques. Extended Semantic Web Conference, 2019
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Jan Portisch and Heiko Paulheim: ALOD2vec Matcher. International Workshop on Ontology Matching, 2018
Jan Portisch, Michael Hladik, Heiko Paulheim: KGvec2go - Knowledge Graph Embeddings as a Service. International Conference on Language Resources and Evaluation, 2020
Jan Portisch, Michael Hladik, Heiko Paulheim: RDF2Vec Light – A Lightweight Approach for Knowledge Graph Embeddings. International Semantic Web Conference, Posters and Demos, 2020.
Jan Portisch, Michael Hladik, Heiko Paulheim: FinMatcher at FinSim-2: Hypernym Detection in the Financial Services Domain using Knowledge Graphs. Workshop on Financial Technology on the Web (FinWeb), 2021.
Jan Portisch, Michael Hladik, Heiko Paulheim: Background Knowledge in Schema Matching: Strategy vs. Data. International Semantic Web Conference, 2021.
Jan Portisch, Heiko Paulheim: Putting RDF2vec in Order. International Semantic Web Conference, Posters and Demos, 2021.
Jan Portisch, Nicolas Heist, Heiko Paulheim: Knowledge Graph Embedding for Data Mining vs. Knowledge Graph Embedding for Link Prediction - Two Sides of the same Coin?. Accepted for publication in Semantic Web Journal.
Petar Ristoski, Stefano Faralli, Simone Paolo Ponzetto, Heiko Paulheim: Large-scale taxonomy induction using entity and word embeddings. International Conference on Web Intelligence, 2017
Petar Ristoski: Exploiting Semantic Web Knowledge Graphs in Data Mining. IOS Press, Studies on the Semantic Web (38), 2019
Petar Ristoski, Anna Lisa Gentile, Alfredo Alba, Daniel Gruhl, Steven Welch: Large-scale relation extraction from web documents and knowledge graphs with human-in-the-loop. Semantic Web Journal (60), 2020
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Bram Steenwinckel, Gilles Vandewiele, Ilja Rausch, Pieter Heyvaert, Ruben Taelman, Pieter Colpaert, Pieter Simoens, Anastasia Dimou, Filip De Turck, Femke Ongenae: Facilitating the Analysis of COVID-19 Literature Through a Knowledge Graph. International Semantic Web Conference, 2020.
Rima Türker: Knowledge-Based Dataless Text Categorization. Extended Semantic Web Conference, 2019
Gilles Vandewiele, Bram Steenwinckel, Pieter Bonte, Michael Weyns, Heiko Paulheim, Petar Ristoski, Filip De Turck, Femke Ongenae: Walk Extraction Strategies for Node Embeddings with RDF2Vec in Knowledge Graphs, arxiv.org, 2020.
Svitlana Vakulenko: Knowledge-based Conversational Search. TU Wien, 2019.
Michael Matthias Voit, Heiko Paulheim: Bias in Knowledge Graphs - an Empirical Study with Movie Recommendation and Different Language Editions of DBpedia. Conference on Language, Data and Knowledge, 2021
Yiwei Wang, Mark James Carman, Yuan Fang Li: Using knowledge graphs to explain entity co-occurrence in Twitter. ACM Conference on Knowledge and Information Management, 2017
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