An online system uses a task async engine to coordinate task execution, such as for phased content creation, where the system enables content providers to efficiently create and publish sponsored content in multiple phases. Each phase of the content creation is represented by a draft of the content. Multiple drafts of the content are stored in a repository of the online system for optimizing content delivery and publication, such as quick identification of conflicts in a draft based on analysis of draft fragments of the draft. Objects associated with the sponsored content are stored in an object model. The connections amongst the various draft segments of a draft are stored in a hierarchy structure. Each user associated with a draft has a role, where all of the roles can contribute to the draft. The online system efficiently publishes the drafts and presents the sponsored content to its target users.