The Database Architectures Research Group at CWI

The Database research group at CWI was established in 1985. It has steadily grown from two PhD students to a group of 17 people ultimo 2011. The group is supported by a scientific programmer and a system engineer to keep our machines running. In this short note, we look back at our past and highlight the multitude of topics being addressed

MonetDB/XQuery - Consistent & Efficient Updates on the Pre/Post Plane

Relational XQuery processors aim at leveraging mature relational DBMS query processing technology to provide scalability and efficiency. To achieve this goal, various storage schemes have been proposed to encode the tree structure of XML documents in flat relational tables. Basically, two classes can be identified: (1) encodings using fixed-length surrogates, like the preorder ranks in the pre/post encoding [5] or the equivalent pre/size/level encoding [8], and (2) encodings using variable-length surrogates, like, e.g., ORDPATH [9] or P-PBiTree [12]. Recent research [1] showed a clear advantage of the former for efficient evaluation of XPath location steps, exploiting techniques like cheap node order tests, positional lookup, and node skipping in staircase join [7]. However, once updates are involved, variable-length surrogates are often considered the better choice, mainly as a straightforward implementation of structural XML updates using fixed-length surrogates faces two performance bottlenecks: (i) high physical cost (the preorder ranks of all nodes following the update position must be modified—on average 50% of the document), and (ii) low transaction concurrency (updating the size of all ancestor nodes causes lock contention on the document root)

MonetDB: Two Decades of Research in Column-oriented Database Architectures

MonetDB is a state-of-the-art open-source column-store database management system targeting applications in need for analytics over large collections of data. MonetDB is actively used nowadays in health care, in telecommunications as well as in scientific databases and in data management research, accumulating on average more than 10,000 downloads on a monthly basis. This paper gives a brief overview of the MonetDB technology as it developed over the past two decades and the main research highlights which drive the current MonetDB design and form the basis for its future evolution

X Python reference manual

This document describes the built-in types, exceptions, and functions of the X windows extension to Python. It assumes basic knowledge about the Python language and access to the X windows documentation. For an informal introduction to the language, see the Python Tutorial. The Python Reference Manual gives a more formal definition of the language. The Python Library Reference describes the built-in and standard modules of Python. This document can be seen as en extension to that document

Adaptive Quality-of-Service Support in Heterogeneous Networks: Results of a Trans-European Experiment

The increasing availability of high-speed networks has served as an enabling technology for applications such as networked multimedia, where a mix of information types can be retrieved from decentralized information stores and presented at a user's workstation. Such transfers work best when a guaranteed amount of network capacity is presented to the application fetching the data. Unfortunately, as the storage of information becomes more decentralized, and as the load on individual information sources and sinks increase, it is often difficult to obtain service guarantees for the duration of a lengthy information exchange-especially when the information access is determined by the dynamic behaviour of users, such as is present in a hypermedia application environment. This project defined an experiment in providing adaptive, runtime control over hypermedia information in a wide-area network. The purpose of the experiment was to determine the adaptive control mechanisms required to provide decentralized access to complex data in an unpredictable networked environment. The unpredictability of the environment may be caused by transient reallocations of network bandwidth, overloading of network servers or reliability problems within the communications infrastructure. In the following sections, we describe the planned and encountered: environment, method and expected results of a series of quality-of-service experiments conducted over moderate-bandwidth links between various European network organizations. We then discuss problems in producing the planned results. We conclude with a travel/expense summary for the project