The Data Model

There are four important concepts that form the data model used throughout S2Graph; services, serviceColumns, labels and properties.

Service, the top level abstraction, act like databases in traditional RDBMS in which all data are contained. At Kakao, a service usually represents one of the company's actual services and is named accordingly, e.g. "KakaoTalk", "KakaoStory".

ServiceColumn are names for vertices and a service can have multiple serviceColumns. For example, a service "KakaoMusic" can have serviceColumn "user_id" and "track_id".

Label, represent relations between two serviceColumns. Think of it as a name for edges. The two serviceColumns can be the same (e.g. for a label representing friendships in an SNS, the two serviceColumns will both be "user_id" of the service). Labels can connect serviceColumns from two different services. For example, one can create a label that stores all events where KakaoStory posts are shared to KakaoTalk.

Properties, are metadata linked to vertices or edges that can be queried upon later. For vertices representing KakaoTalk users, date_of_birth is a possible property, and for edges representing similar KakaoMusic songs their similarity_distance can be a property.

Using these abstractions, a unique vertex can be identified with its (service, column, vertex id), and a unique edge can be identified with its (service, label, source vertex id, target vertex id). Additional information on edges and vertices are stored within their properties.