Ning Gu

Consistency maintenance based on the mark & retrace technique in groupware systems

Replicated architecture is widely used for concealing network delay. However, consistency maintenance in fully replicated architecture is a major technical challenge. In this paper, we report a Mark & Retrace based method in replicated groupware systems. Compared with the Operation Transformation technique, it does not adjust the operations position but retraces the documents address space to the state at the time of the operations generation. Then the operation can be executed directly in this address space. Mark & Retrace method can not only achieve the same goal of consistency maintenance but also provide a better support for Undo. This paper provides the proof of the algorithms correctness of consistency maintenance, in which both the orders of character nodes and marks of each node at all sites are kept consistent. Furthermore, the amortized efficiency can reach O(log n).

Interest-based real-time content recommendation in online social communities

The fast-growing popularity of online social communities and the massive amounts of user-generated content pose a critical need for, and new challenges on, content recommender system. The system needs to identify the unique and diverse interests of individual users and deliver content to interested users on a real-time basis. In this work, we propose Farseer, a system for personalized real-time content recommendation and delivery in online social communities. The proposed solution consists of a set of integrated offline and online algorithms that identify and utilize unique item-based interest clusters and cluster-based item rating in order to recommend newly-generated content items to individual users in real time. Our main contributions are (1) a detailed analysis of content popularity distribution and user interest distribution in online social communities; (2) a novel interest-based clustering and cluster-based content recommendation solution; and (3) a complete implementation and deployment in an online social community. Evaluation results gathered from real-world user studies demonstrate that the proposed system outperforms three widely-used collaborative filtering algorithms (kNN, PLSA, SVD) in existing recommender systems. It can effectively identify personal interests and improve the quality and efficiency of real-time personalized content recommendation in online social communities.

PBmice: an integrated database system of piggyBac (PB) insertional mutations and their characterizations in mice

DNA transposon piggyBac (PB) is a newly established mutagen for large-scale mutagenesis in mice. We have designed and implemented an integrated database system called PBmice (PB Mutagenesis Information CEnter) for storing, retrieving and displaying the information derived from PB insertions (INSERTs) in the mouse genome. This system is centered on INSERTs with information including their genomic locations and flanking genomic sequences, the expression levels of the hit genes, and the expression patterns of the trapped genes if a trapping vector was used. It also archives mouse phenotyping data linked to INSERTs, and allows users to conduct quick and advanced searches for genotypic and phenotypic information relevant to a particular or a set of INSERT(s). Sequence-based information can be cross-referenced with other genomic databases such as Ensembl, BLAST and GBrowse tools used in PBmice offer enhanced search and display for additional information relevant to INSERTs. The total number and genomic distribution of PB INSERTs, as well as the availability of each PB insertional LINE can also be viewed with user-friendly interfaces. PBmice is freely available at http://www.idmshanghai.cn/PBmice or http://www.scbit.org/PBmice/.

An algorithm for selective undo of any operation in collaborative applications

Selective undo allows users to undo any operation in the history and is considered a key feature in collaborative applications. Operational transformation (OT) is a powerful tool for implementing selective undo because it can be used to rearrange operations in a history in arbitrary orders. Despite the significant progress over the past two decades, however, there is still a space for improvements. Most existing works take time quadratic or even exponential in the size of the operation history H to undo an operation. Although this might be acceptable for real-time collaboration, it would be suboptimal in mobile and asynchronous collaborative applications in which a long history may accumulate. In addition, it is important to prove an algorithm with regard to the correctness criteria it assumes. This paper proposes a novel OT-based algorithm that provides integrated do and selective undo. The algorithm achieves time complexity of O(|H|) in both do and undo by keeping the history in a special operation effects relation order. Its correctness is formally proved with regard to formalized, provable conditions that are extended from a recent theoretical framework.

Service Registration and Discovery in a Domain-Oriented UDDI Registry

As a part of Web services triangle architecture, UDDI registry takes on the task of service registration and discovery, which plays an important role in the open, distributed and dynamic Web services environment. However, the current UDDI registries cannot meet the needs of practical applications. This paper proposes a domain-oriented UDDI registry architecture and addresses some new concepts such as service property schema, service relationship and service constraint. Compared with other extended UDDI registries, this architecture can improve the usability and operability of UDDI registry a great deal, fulfill the requirements of some applications more friendly and thus is very suitable for some specific domains

An operational transformation based synchronization protocol for web 2.0 applications

Current Web 2.0 services are making mass collaboration a reality. Using a Web browser, people can participate in cooperative work anytime, anywhere from any computing device as long as there is an Internet connection. Lying in the heart of some well-known services is an optimistic consistency control technique called operational transformation (OT). This paper proposes TIPS, a novel sync protocol that adapts OT for Web 2.0 applications. Based on a recent theoretical framework called ABT, it ensures not only convergence but also the right object order for linear documents. Designed to address the HTTP style of communication, TIPS allows clients to sync with the server by independent time intervals and dynamically join and leave at any time. When processing do operations, its time complexity is linear in the total number of operations generated by all clients during one server interval and independent of the size of history. TIPS is efficient for supporting a spectrum of (near-)realtime to asynchronous collaboration editing tasks.

A sequence transformation algorithm for supporting cooperative work on mobile devices

Operational transformation (OT) is a promising technique for supporting collaboration using mobile devices because it allows users to work on local data replicas even in a disconnected mode. However, as work goes mobile, a large number of operations may accumulate, defying the capacity of current OT algorithms that are mostly designed for real-time group editing. Since their assumption is that operations are propagated frequently, they generally only address how to integrate one remote operation at a time. As a consequence, most algorithms take O(|H|2) to integrate one operation and thus O(|H|3) to integrate a long sequence, where H is the operation history. This paper proposes a novel algorithm that provides optimized transformation of long sequences, improving the time complexity to O(|H|). Our experiments will show that it takes 59 minutes in a recent algorithm versus 1.5 seconds in this work to integrate two long sequences on a mobile device. The performance improvement is critical towards achieving desired responsiveness and group productivity in a class of mobile collaborative applications.

Lock-free consistency control for web 2.0 applications

Online collaboration and sharing is the central theme of many web-based services that create the so-called Web 2.0 phenomena. Using the Internet as a computing platform, many Web 2.0 applications set up mirror sites to provide large-scale availability and to achieve load balance. However, in the age of Web 2.0, where every user is also a writer and publisher, the deployment of mirror sites makes consistency maintenance a Web scale problem. Traditional concurrency control methods (e.g. two phase lock, serialization, etc.) are not up to the task for several reasons. First, large network latency between mirror sites will make two phase locking a throughput bottleneck. Second, locking will block a large portion of concurrent operations, which makes it impossible to provide large-scale availability. On the other hand, most Web 2.0 operations do not need strict serializability - it is not the intention of a user who is correcting a typo in a shared document to block another who is adding a comment, as long as consistency can still be achieved. Thus, in order to enable maximal online collaboration and sharing, we need a lock-free mechanism that can maintain consistency among mirror sites on the Web. In this paper, we propose a flexible and efficient method to achieve consistency maintenance in the Web 2.0 world. Our experiments show its good performance improvement compared with existing methods based on distributed lock.

Reliving the Past & Making a Harmonious Society Today: A Study of Elderly Electronic Hackers in China

This paper tells a story of DIY (do it yourself) making that does not neatly fit more familiar narratives of making: as individual empowerment, as a democratizing force, and as technoscientific innovation. Drawing on ethnographic research with a collective of elderly electronic hackers in China, we provide insights into the socio-technical and politico-economic processes of hacking and making. This paper examines how the activity of making functioned for elderly DIY enthusiasts as way of remaking and reliving the past and as a means for expressing class belonging and citizenship. We show that making and hacking is not practiced in a void independent of social, political or economic forces. Rather, making unfolds in relation to, and is contingent on, societal norms and specific techno-cultural histories. As much as hacking empowers certain people, it excludes others and functions as a site for the exercise of power and social distinction making.

A Fast Operational Transformation Algorithm for Mobile and Asynchronous Collaboration

In a mobile collaboration environment, the shared files are often replicated so that the users can work in parallel during periods of disconnection. When reconnected, sequences of updates made by different users are merged to produce a consistent view of shared files. This paper presents a novel transformation-based merging algorithm for supporting mobile collaboration. Compared to alternative optimistic consistency control methods, it can merge any updates to the same file automatically at the finest granularity without causing loss of work. Moreover, it improves the time complexity of the state-of-the-art transformation-based merging algorithms from O(n3) to O(n), where n is the size of either sequence when their sizes are comparable. This improvement is drastic and important especially for mobile devices that run on batteries and have limited processing power.