Maintaining consistency in collaboration over hierarchical documents

Abstract

Collaboration is a key requirement of teams of individuals working together towards some common goal. Computer-supported collaboration is an increasingly common occurrence, driven by the evolving global nature of business, science and engineering and enabled by improvements in computing and communication technologies. Collaborative editing systems have been developed to support a group of people editing a document collaboratively over a computer network. Since not all user groups have the same conventions and not all tasks have the same requirements, it is important to support collaboration for various types of documents. Moreover, since a task has a set of development stages that require various forms of activity, customisation of the collaborative environment should be offered to support different modes of working between different sub-communities of users at different points in time. The goal of this thesis was to investigate different settings for collaboration over the most common types of documents, such as textual, graphical and XML, with the aim of building a general theoretical framework to support the development of a range of collaborative editors. A key issue for a general framework for collaboration is a common model that abstracts a large class of documents. The hierarchical model encompasses a wide range of documents and offers support for semantically structured documents. XML documents conform to a hierarchical structure by definition. We modeled text documents using a tree, where the document consists of a sequence of paragraphs, each paragraph of a sequence of sentences, each sentence as a sequence of words and each word as a sequence of characters. Graphical documents are also modeled by a hierarchical structure: groups are represented as internal nodes, while simple objects are represented as leaves. In order to work in a uniform way with different semantic units of the document, we adopted a multi-level editing approach where we associated with an element of the document the editing operations targeting that element. Operational transformation is a suitable mechanism for maintaining