Managing peer database transactions

当今的教育、科学、商业和政府所依赖的许多数据源已经产生了越来越多的异构性、网络化和以各种格式存储的海量数据。我们过去的工作有助于建立关系数据库网络(称为对等数据库，或简称为对等数据库)，使如此大量的数据可供共享。对等数据库使用对等(P2P)网络共享数据。P2P网络是点对点的通信基础设施，对等设备在共享数据之前使用它来建立熟人。确保数据以一种具有语义意义的方式跨越异质边界共享一直是我们研究的核心。我们与其他人合作，开发了一个原型对等数据库管理系统(PDBMS)，它使用所谓的映射表来解决异构性问题。映射表是数据值之间以及不同对等点的模式元素之间的对应关系。使用映射表，PDBMS通常与远程对等体建立熟人，使用来自熟知对等体的数据回答查询，并将本地更新传播到远程对等体。我们的研究计划有两个主要目标，一是为PDBMS设置设计高级交易模型，二是在我们现有的PDBMS基础设施上实现这些交易模型。由于PDBMS类似于传统的多数据库系统，其中的本地数据源不是集成的，而是协调的，我们仔细研究了为传统的多数据库系统提出的事务模型，放松了许多假设，并增加了更适合PDBMS环境的新的事务模型。我们处理的主要问题是本地对等交易之间的关系，后者的一致性，跨大量对等交易的并发控制和恢复。*我们的目标是使面向最终用户的互联网数据共享的愿景成为可能。用户将只需要专注于他们的本地数据，而与远程同行的互操作性的错综复杂将在系统级别尽可能自动地处理。

Many of the data sources upon which today's education, science, business, and government depend have been generating increasingly heterogeneous, networked, and vast amounts of data stored in a variety of formats. Our past work has contributed to building networks of relational databases (called peer databases, or simply peers) that make such a gigantic amount of data available for sharing. Peer databases share data using a peer-to-peer (P2P) network. A P2P network is point-to-point  communication infrastructure which is used by peers to establish acquaintances prior to sharing data. Ensuring data sharing across heterogeneous boundaries in a semantically meaningful way has been at the core of our research.  In collaroration with others, we have produced a prototype peer database management system (PDBMS) that uses the so-called mapping tables to solve the heterogeneity problem. Mapping tables are correspondences between data values as well as between schema elements at different peers. Using mapping tables, a PDBMS typically establishes acquaintances with remote peers, answers queries using data originating in acquainted peers, and propagate local updates to remote peers. Our research program has two main objectives which are to design advanced transaction models for the PDBMS setting, and to implement these transaction models on top our existing PDBMS infrastructure. Since PDBMSs are similar to traditional multidatabase systems in which the local data sources are not integrated, but rather coordinated, we closely examine the transaction models proposed for traditional multidatabase systems and relax many of their assumptions, as well as we add new ones that are more suitable for the PDBMS setting. The main issues we deal with are the relationship among local peer transactions, the consistency of the latter, concurrency control and recovery across a large amount of peers.  We aim at making the vision of  end-user oriented Internet data sharing possible. Users will only need to focus on their local data while the intricacies of the interoperability with remote peers will be handled as automatically as possible at the system level.