Lock-based Protocols for Cooperation on XML Documents

The eXtensible Markup Language (XML) is well accepted in several different Web application areas. As soon as many users and applications work concurrently on the same collection of XML documents - e.g. on an XML database via a Web interface - isolating accesses and modifications of different transactions becomes an important issue. We discuss four different core protocols for synchronizing access to and modifications of XML document collections. These core protocols synchronize structure traversals and modifications. They are meant to be integrated into a native XML base management System (XBMS) and are based on two phase locking. We also demonstrate the different degrees of cooperation that are possible with these protocols by various experimental results. Furthermore, we also discuss extensions of these core protocols to full-fledged protocols. Further, we show how to achieve a higher degree of concurrency by exploiting the semantics expressed in Document Type Definitions (DTDs)

Isolation in XML Bases

The eXtensible Markup Language (XML) is well accepted in many different application areas. As a consequence, there is an increasing need for persistently storing XML documents. As soon as many users and applications work concurrently on the same collection of XML documents - i.e. an XML base - isolating accesses and modifications of different transactions becomes an important issue. We discuss six different core protocols for synchronizing access to and modifications of XML document collections. These core protocols synchronize structure traversals and modifications. They are meant to be integrated into a native XML base management System (XBMS). Four of the six core protocols are based on two phase locking, one uses time stamps, and the last one uses a novel dynamic commit-ordering approach. The latter two protocols achieve a higher degree of concurrency by a novel implicit representation of multiple versions. We also discuss extensions of these core protocols to full-fledged protocols. Further, we show how the two phase locking based protocols can achieve a higher degree of concurrency by exploiting the semantics expressed in Document Type Definitions (DTDs)

Developing Collaborative XML Editing Systems

In many areas the eXtensible Mark-up Language (XML) is becoming the standard exchange and data format. More and more applications not only support XML as an exchange format but also use it as their data model or default file format for graphic, text and database (such as spreadsheet) applications. Computer Supported Cooperative Work is an interdisciplinary field of research dealing with group work, cooperation and their supporting information and communication technologies. One part of it is Real-Time Collaborative Editing, which investigates the design of systems which allow several persons to work simultaneously in real-time on the same document, without the risk of inconsistencies. Existing collaborative editing research applications specialize in one or at best, only a small number of document types; for example graphic, text or spreadsheet documents. This research investigates the development of a software framework which allows collaborative editing of any XML document type in real-time. This presents a more versatile solution to the problems of real-time collaborative editing. This research contributes a new software framework model which will assist software engineers in the development of new collaborative XML editing applications. The devised framework is flexible in the sense that it is easily adaptable to different workflow requirements covering concurrency control, awareness mechanisms and optional locking of document parts. Additionally this thesis contributes a new framework integration strategy that enables enhancements of existing single-user editing applications with real-time collaborative editing features without changing their source code