Preface to the Special Issue on Graph Data Management in Online Social Networks.

We are delighted to present this special issue of World Wide Web on Graph Data Management in Online Social Networks. The purpose of this special issue is to bring together some recent and significant results in analysing OSNs with novel graph data management techniques in a timely fashion. In "Dolha - an Efficient and Exact Data Structure for Streaming Graphs" the authors present a new memory efficient graph data structure called Dolha to support massive graph storage and frequent update in modern applications. [Extracted from the article]