SoK: Exploring Blockchains Interoperability

Distributed ledger technologies like blockchain have gained great attention in both academia and industry. Blockchain as a potentially disruptive technology can advance many different fields, e.g., cryptocurrencies, supply chains, and the industrial Internet of Things. The next-generation blockchain ecosystem is expected to consist of various homogeneous and heterogeneous distributed ledgers. These ledger systems will inevitably require a certain level of proper cooperation of multiple blockchains to enrich advanced functionalities and enhance interoperable capabilities for future applications. The interoperability among blockchains will definitely revolutionize current blockchain design principles, like the emergence of Internet. The development of cross-blockchain applications involves much complexity regarding the variety of underlying cross-blockchain communication. The way to effectively enable interoperability across multiple blockchains is thus essential and expecting to confront various unprecedented challenges. For instance, due to different transaction structures, ensuring the properties of ACID (Atomicity, Consistency, Isolation, Durability) in transactions processing and verification processes across diverse blockchain systems remains a challenging task in both academia and industry. This paper provides a systematic and comprehensive review of the current progress of blockchain interoperability. We explore both general principles and practical schemes to achieve interoperable blockchain systems. We then survey and compare the state-of-the-art solutions to deal with the interoperability of blockchains in detail. Finally, we discuss several critical challenges and some potential research directions to advance the research on exploring blockchain interoperability

DBMS Architecture -- Still an Open Problem

More than two decades ago, DB researchers faced up to the question of how to design a data-independent database management system (DBMS), that is, a DBMS which offers an appropriate application programming interface (API) to the user and whose architecture is open for permanent evolution. For this purpose, an architectural model based on successive data abstraction steps of record-oriented data was proposed as kind of a standard and later refined to a five-layer hierarchical DBMS model. We review the basic concepts and implementation techniques of this model and survey the major improvements achieved in the system layers to date. Furthermore, we consider the interplay of the layered model with the transactional ACID properties and again outline the progress obtained. In the course of the last 20 years, this DBMS architecture was challenged by a variety of new requirements and changes as far as processing environments, data types, functional extensions, heterogeneity, autonomy, scalability, etc. are concerned. We identify the cases which can be adjusted by our standard system model and which need major extensions or other types of system models