cayleygraph/cayley

Cayley is an open source database for what is called Linked Data. Most databases people meet first, like MySQL or PostgreSQL, store information in tables of rows and columns. A graph database like Cayley instead stores facts as small connected pieces, with each fact saying that one thing is related to another thing in some way. That shape is well suited to questions about how items connect, for example which films star a given pair of actors. The project was inspired by the graph database behind Google's Knowledge Graph, which itself grew out of an earlier project called Freebase. The code is written in Go. According to the README, Cayley comes with a built-in query editor, a visualizer, and a REPL, so a user can run queries and see the results without setting up a separate front end. It supports more than one query language. Gizmo is inspired by Gremlin, which is a query language used in other graph databases. There is also a query language modelled on GraphQL, and MQL, a simplified language carried over from Freebase. The README highlights three other properties. Cayley is described as modular, meaning it can be connected to different programming languages and to different storage back ends rather than being tied to one. It is described as production ready and as used by several companies for real workloads. The maintainers also include a rough performance note: on 2014 consumer hardware with an average disk, 134 million quads stored in LevelDB are handled without trouble, and a two-hop intersection query, such as films starring two given people, takes about 150 milliseconds. The project documentation lives on GitBook, with a link from the README. There is also a Snap Store badge for installing Cayley on Linux through the Snap package system. Community channels listed include the cayley.io website, a Slack workspace, a Discourse forum that can be used as a mailing list, a Twitter account, and a contributing guide for people who want to send patches. The README itself is short and acts mostly as a starting page that points at those other resources.