Tuesday, February 24, 2009

Database -A collection of information

A collection of information organized in such a way that a computer program can quickly select desired pieces of data. You can think of a database as an electronic filing system.

Traditional databases are organized by fields, records, and files. A field is a single piece of information; a record is one complete set of fields; and a file is a collection of records. For example, a telephone book is analogous to a file. It contains a list of records, each of which consists of three fields: name, address, and telephone number.

An alternative concept in database design is known as Hypertext. In a Hypertext database, any object, whether it be a piece of text, a picture, or a film, can be linked to any other object. Hypertext databases are particularly useful for organizing large amounts of disparate information, but they are not designed for numerical analysis.

To access information from a database, you need a database management system (DBMS). This is a collection of programs that enables you to enter, organize, and select data in a database.

Friday, February 13, 2009

DEC Alpha

Alpha, originally known as Alpha AXP, was a 64-bit reduced instruction set computer (RISC) instruction set architecture (ISA) developed by Digital Equipment Corporation (DEC), designed to replace the 32-bit VAX complex instruction set computer (CISC) ISA and its implementations. Alpha was implemented in microprocessors originally developed and fabricated by DEC. It was used in a variety of DEC workstations and servers, eventually forming the basis for almost their entire mid-to-upper-scale lineup. Several third-party vendors also produced Alpha systems, as well as PC compatible form factor motherboards.

Alpha supports both the OpenVMS (previously known as OpenVMS AXP) operating system and Tru64 UNIX (previously known as DEC OSF/1 AXP and Digital UNIX). Open source operating systems also run on the Alpha, notably Linux and BSD UNIX flavors (FreeBSD support ended as of 7.0). Microsoft supported the processor in Windows NT until NT 4.0 SP6 but did not extend Alpha support beyond RC1 of Windows 2000.

Monday, February 09, 2009


In computer science, a B-tree is a tree data structure that keeps data sorted and allows searches, insertions, and deletions in logarithmic amortized time. Unlike self-balancing binary search trees, it is optimized for systems that read and write large blocks of data. It is most commonly used in databases and file systems.

In B-trees, internal (non-leaf) nodes can have a variable number of child nodes within some pre-defined range. When data is inserted or removed from a node, its number of child nodes changes. In order to maintain the pre-defined range, internal nodes may be joined or split. Because a range of child nodes is permitted, B-trees do not need re-balancing as frequently as other self-balancing search trees, but may waste some space, since nodes are not entirely full. The lower and upper bounds on the number of child nodes are typically fixed for a particular implementation. For example, in a 2-3 B-tree (often simply referred to as a 2-3 tree), each internal node may have only 2 or 3 child nodes.

Monday, February 02, 2009


XQuery is a query language (with some programming language features) that is designed to query collections of XML data. It is semantically similar to SQL.

XQuery 1.0 was developed by the XML Query working group of the W3C. The work was closely coordinated with the development of XSLT 2.0 by the XSL Working Group; the two groups shared responsibility for XPath 2.0, which is a subset of XQuery 1.0. XQuery 1.0 became a W3C Recommendation on January 23, 2007.

"The mission of the XML Query project is to provide flexible query facilities to extract data from real and virtual documents on the World Wide Web, therefore finally providing the needed interaction between the Web world and the database world. Ultimately, collections of XML files will be accessed like databases".