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Btrieve is a transactional database (navigational database) software product. It is based on Indexed Sequential Access Method (ISAM), which is a way of storing data for fast retrieval. 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, 32-bit IBM OS/2 and for Novell NetWare. It was originally a record manager published by SoftCraft. Btrieve was written by Doug Woodward and Nancy Woodward and initial funding was provided in part by Doug's brother Loyd Woodward. Around the same time as the release of the first IBM PCs, Doug received 50% of the company as a wedding gift and later purchased the remainder from his brother. After gaining market share and popularity, it was acquired from Doug and Nancy Woodward by Novell in 1987, for integration into their Netware operating system in addition to continuing with the MS-DOS version. The product gained significant market share as a database embedded in mid-market applications in addition to being embedded in every copy of NetWare 2.x, 3.x and 4.x since it was available on every NetWare network. After some reorganization within Novell, it was decided in 1994 to spin off the product and technology to Doug and Nancy Woodward along with Ron Harris, to be developed by a new company known as Btrieve Technologies, Inc. (BTI). Btrieve was modularized starting with version 6.15 and became one of two database front-ends that plugged into a standard software interface called the Micro-Kernel Database Engine. The Btrieve front-end supported the Btrieve API and the other front-end was called Scalable SQL, a relational database product based upon the MKDE that used its own variety of Structured Query Language, otherwise known as SQL. After these versions were released (Btrieve 6.15 and ScalableSQL v4) the company was renamed to Pervasive Software prior to their IPO. Shortly thereafter the Btrieve and ScalableSQL products were combined into the products now known and sold as Pervasive.SQL or PSQL. Btrieve continued for a few years while ScalableSQL was quickly dropped. Customers were encouraged to upgrade to Pervasive.SQL which supported both SQL and Btrieve applications. ==Architecture== (詳細は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 enabled 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, whereas 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 make data recovery easier. The Btrieve file format consists entirely of pages, which are the data that move between memory and storage 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 were used. Logical are mapped to physical pages (pages at a fixed location in the file) on the disk by 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. To avoid database corruption, Btrieve uses two methods of updating records: ''pre-image paging'' in Btrieve versions before 6.0, and ''shadow paging'' in subsequent versions. It was primarily the change-over from pre-image paging to shadow-paging, which necessitated radical file format changes, that caused compatibility issues between version 6 and previous versions. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Btrieve」の詳細全文を読む スポンサード リンク
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