Knowledge Graphs

“Knowledge Graphs”
Communications of the ACM, March 2021, Vol. 64 No. 3, Pages 96-104
Review Articles
By Claudio Gutierrez, Juan F. Sequeda

“Tracking the historical events that lead to the interweaving of data and knowledge.”

“Those who cannot remember the past are condemned to repeat it.”
—George Santayana

The notion of Knowledge Graph stems from scientific advancements in diverse research areas such as Semantic Web, databases, knowledge representation and reasoning, NLP, and machine learning, among others. The integration of ideas and techniques from such disparate disciplines presents a challenge to practitioners and researchers to know how current advances develop from, and are rooted in, early techniques.

Understanding the historical context and background of one’s research area is of utmost importance in order to understand the possible avenues of the future. Today, this is more important than ever due to the almost infinite sea of information one faces everyday. When it comes to the Knowledge Graph area, we have noticed that students and junior researchers are not completely aware of the source of the ideas, concepts, and techniques they command.

The essential elements involved in the notion of Knowledge Graphs can be traced to ancient history in the core idea of representing knowledge in a diagrammatic form. Examples include: Aristotle and visual forms of reasoning, around 350 BC; Lull and his tree of knowledge; Linnaeus and taxonomies of the natural world; and in the 19th. century, the works on formal and diagrammatic reasoning of scientists like J.J. Sylvester, Charles Peirce and Gottlob Frege. These ideas also involve several disciplines like mathematics, philosophy, linguistics, library sciences, and psychology, among others.

This article aims to provide historical context for the roots of Knowledge Graphs grounded in the advancements of the computer science disciplines of knowledge, data, and the combination thereof, and thus, focus on the developments after the advent of computing in its modern sense (1950s). To the best of our knowledge, we are not aware of an overview of the historical roots behind the notion of knowledge graphs. We hope that this article is a contribution in this direction. This is not a survey, thus, necessarily does not cover all aspects of the phenomena and does not do a systematic qualitative or quantitative analysis of papers and systems on the topic.

This article is the authors’ choice of a view of the history of the subject with a pedagogical emphasis directed particularly to young researchers. It presents a map and guidelines to navigate through the most relevant ideas, theories, and events that, from our perspective, have triggered current developments. The goal is to help understand what worked, what did not work, and reflect on how diverse events and results inspired future ideas.

For pedagogical considerations, we periodized the relevant ideas, techniques, and systems into five themes: Advent, Foundations, Coming-of-Age, Web Era, and Large Scale.

They follow a timeline, although with blurry boundaries. The presentation of each period is organized along two core ideas—data and knowledge—plus a discussion on data+knowledge showing their interplay. At the end of each section, we sketched a list of “realizations” (in both its senses—of becoming aware of something, as well as achievements of something desired or anticipated), and “limitations” (or, impediments) of the period. The idea is to motivate a reflection on a balance of the period. At the end of each section we include a paragraph indicating references to historical and/or technical overviews on the topics covered.

[Sections covered include:

Advent of the Digital Age

Data and Knowledge Foundations

Coming-of-Age of Data and Knowledge

Data, Knowledge, and the Web

Data and Knowledge at Large Scale

Where Are We Now?]

Where Are We Now?

A noticeable phenomenon in the history we have sketched is the never-ending growth of data and knowledge, in both size and diversity. At the same time, an enormous diversity of ideas, theories, and techniques were being developed to deal with it. Sometimes they reached success and sometimes ended in failure, depending on physical and social constraints whose parameters most of the time were far out of the researcher’s control.

In this framework, historical accounts can be seen as a reminder that absolute success or failure does not exist, and that each idea, theory, or technique needs the right circumstances to develop its full potential. This is the case with the notion of Knowledge Graphs. In 2012, Google announced a product called the Google Knowledge Graph. Old ideas achieved worldwide popularity as technical limitations were overcome and it was adopted by large companies. In parallel, other types of “Graph” services were developed, as witnessed by similar ideas by other giants like Microsoft, Facebook, Amazon and Ebay. Later, myriad companies and organizations started to use the Knowledge Graph keyword to refer to the integration of data, given rise to entities and relations forming graphs. Academia began to adopt this keyword to loosely designate systems that integrate data with some structure of graphs, a reincarnation of the Semantic Web, and Linked Data. In fact, today the notion of Knowledge Graph can be considered, more than a precise notion or system, an evolving project and a vision.

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