SVGDoc: A CRDT for Collaborative Vector Graphics Editing

Conflict-free Replicated Data Types (CRDTs) are a class of algorithms that allow decentralized editing of documents as data structures in which concurrent operations are commutative, while there has been extensive research on generic CRDTs which allow CRDTs to be modeled according to application data. Current generic CRDTs use a CRDT map or an operation log which lack a tree structure with support for move operations to represent a vector graphics document or does not preserve updates that are concurrent to deletions. In this paper, a set of concurrent editing scenarios that are frequently made by user's of collaborative vector graphics editing are described. A CRDT for collaborative vector graphics editing which cover these scenarios named SVGDoc is then introduced. The main idea of SVGDoc is to use the UWMap (Update-Wins Map) as described by Preguica to allow updates to be preserved when concurrently made to deletions in combination with the move operation log described by Kleppmann et al to allow move operations among nodes in a tree. SVGDoc is also tested through unit testing and further validated by applying it to a minimal collaborative vector graphics editor.