Jet is the Database Management System (DBMS) which underlies Microsoft Access and also Visual Basic, as well as MS Word and MS Excel.
The Jet engine (Joint Engine Technology) was developed by Microsoft in the early 1990’s as an answer to rapidly shifting needs of database systems users and applications developers. Although still relevant, reliance on the once mighty Jet engine is set to erode as limitations to the technology have become apparent and seemingly more effective alternatives have begun to present themselves. Moves are afoot to replace Jet as the pre-eminent DBMS engine, and these changes will inevitably affect MS Access users and developers throughout the industry as future versions of the product undergo fundamental changes to the back-end.
Just as Jet was the solution to the problems of the eighties and early nineties, the tailored solution to the problems of the next fifteen years will be different. Microsoft have cut back investment in the Jet technology for future products, instead focusing on SQL Server as the future of Database Management.
But for now, Jet remains a first-class technology in terms of the fundamental requirements of a database engine. Indeed, for a great many organisations, the narrower scope of the Jet engine for a limited number of users will remain the most practical, most cost-effective solution in the short to medium term.
Jet is a collection of components, mostly DLLs (dynamic link libraries), which together form a platform for robust, multi-user database generation, editing, and querying. Jet handles all of the database processing for Microsoft Access and Visual Basic. The Jet engine also can provide data to Open DataBase Connectivity (ODBC) client applications using the Microsoft Access 2.0 ODBC driver.
The Jet engine can be said to be comprised of two broad components:- a Data Definition Language to create and edit the data structures, and a Data Manipulation Language used for adding, editing and deleting data, and for querying.
Jet stores data according to ISAM, the ‘Indexed Sequential Access Method’. Queries are performed by the ‘Jet Query Engine’, which uses SQL to read off the ISAM indexed data.
A ‘Replication Engine’ is included, the purpose of which is to replicate database structures on multiple systems, with periodic synchronisation.
Data is stored in the form of .mdb files. A single .mdb file can store data from hundreds of tables, as well as indexes and relations between those tables, and a great deal more besides. Entity integrity and referential integrity of the database is supported at the engine level, making Jet particularly adept in this regard.
Security is built in to the Jet engine, and takes two forms. User and group accounts provide password-protected security and differing levels of access, while security is built into the tables themselves in the form of ‘Object Permissions’, which protect data from malicious would-be users from the inside.
Data from a legacy system can be incorporated into the Jet DBMS, even if that data has to be kept in it’s original format for use with the legacy system. This snazzy feature is also a distinct advantage to those sharing data across multiple non-integrated systems.
Jet, as the brains behind MS Access, has proved to be exceptionally efficient in terms of generating databases quickly and easily - particularly for single users or small teams. Access is the most popular desktop database application in the world today, and it’s popularity is due in no small part to the broad effectiveness of the Jet engine in accomplishing all necessary database handling tasks, from creation to security to multi-user support. The sheer weight of Jet expertise and applications make it still a powerful and relevant tool, and it remains to be seen if future non-Jet powered products will be as broadly effective.