Games - Btrieve

	Games - Btrieve

In computing, Btrieve is a transactional database based on Indexed Sequential Access Method (ISAM), a way of storing data for fast retrieval. Btrieve was modularised in version 6.15 and became one of two database backends that plugged into a standard software interface called the Micro-Kernel Database Engine (the other product is Scalable SQL, a relational database product that uses Structured Query Language, otherwise known as SQL). There have been several versions of the product for DOS, Linux, older versions of Microsoft Windows, Windows 98, Windows NT, Windows 2000, Windows XP, Windows Server 2003 and for Novell Netware.

It was originally a record manager that was shipped by SoftCraft at around the same time as the release of the first IBM PCs. After gaining market share and popularity, it was purchased by Novell for integration into their Netware operating system. The product failed to gain significant market share and, after some reorganisation within Novell, the product was spun off to be developed by a new company known as Btrieve Technologies, Inc. (or BTI). After several new versions were released the company was renamed to Pervasive Software and they now sell a product called Pervasive PSQL that can use both Btrieve and SQL.

Architecture

Btrieve is not a relational database management system (RDBMS). Early descriptions of Btrieve referred to it as a record manager (though Pervasive initially used the term navigational database but later changed this to transactional database) because it only deals with the underlying record creation, data retrieval, record updating and data deletion primitives. It uses ISAM as its underlying indexing and storage mechanism. A key part of Pervasive's architecture is the use of a MicroKernel Database Engine, which allows different database backends to be modularised and integrated easily into their DBMS package, Pervasive.SQL. This has allowed them to support both their Btrieve navigational database engine and an SQL-based engine, Scalable SQL.

Current versions of Btrieve support system transactions and user transactions, where system transactions are a bundle of non-transactional operations and/or user transactions, while user transactions are transactions that work on actual data in the database. System transactions were developed to allow multiple transactions to be done in a batch and to allow the ability to recover data more easily.

The Btrieve file format consists entirely of pages, which are the data that moves between memory and storage media when the engine performs an I/O operation. Versions prior to 6.0 merely used data pages, index pages and a file control record (FCR). The file had an index for searching that linked to physical pages. Beginning with version 6.0 logical pages started to be used, which are pages that are mapped to physical pages (pages at a fixed location in the file) on the disk through the use of a set of page allocation tables (PATs). The FCR is a record that contains important information about Btrieve files, such as the number of pages in current use. In order to avoid corruption in the database Btrieve uses two methods of updating records: pre-image paging in Btrieve versions before 6.0 and shadow paging in subsequent versions. It was mainly the change-over from pre-image paging to shadow-paging that caused radical file format changes that broke compatibility between previous versions of Btrieve and version 6.x of the product.

History

Btrieve has been owned and developed by three different companies: SoftCraft, Novell and Btrieve Technologies, Inc. (later renamed Pervasive Software). They have a committed and loyal developer-base and in all the company's literature they remain fully committed to the product; in fact, Pervasive have even set up a that recognises existing developers.

SoftCraft years

The product was launched in February 1982 by SoftCraft, a firm located in Austin, Texas, by Doug and Nancy Woodward. Doug became the vice-president and handled software development, and Nancy became the president of the company. They released a number of versions over the next few years: in February 1983 they released the Btrieve 2.x series, and when MS-DOS 2.x developed support for file and directory handles they released Btrieve 3.0. When MS-DOS 3.1 standardised its internal interfaces in March 1985 they released Btrieve 3.1 C/S one month later, which had network and client/server support. In February 1986 Btrieve 4.0 was released, and when the 4.1 upgrade was released it gained support for extended key types and supplemental indexes.

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