Data Access Language: Difference between revisions

Revision as of 17:22, 29 May 2005

Revision as of 20:17, 2 August 2005

Line 1:

'''Data Access Language''', or simply '''DAL''', was a [[SQL]]-like language parser released by [[Apple]] in 1990 to provide unified [[client/server]] access to [[database management system]]s.

==History==

DAL started as a 3rd party product, '''CL/1''' (''Connectivity Language One''), from a small vendor, Network Innovations. Apple purchased the company in 1988, about the time that client/server databases were becoming a hot issue in the industry. They released their first version of the re-branded software in 1989, for [[MVS]], and followed with other versions over the next year or so.

DAL suffered from most Apple problems of the early 1990s, notably a alternating level of support in which Apple would presentaggressively promote the product and then ignore it. DAL's release was also coincident with Apple's fall from grace in the business world, and not coincidentally with [[Microsoft]]'s [[ODBC]] efforts. It

DAL appears to have seen little use, and eventually Apple sold it to tiny Independence Technologies in 1994, during a sell-off of a number of "high-end" packages such as their [[X.400]] server and an [[Systems Network Architecture|SNA]] client. In 1995 [[BEA Systems]] bought the company, and in turn sold it to [[Uniprise]] in late 1996. During this period it was basically a dead product.

==Description==

DAL was essentially a cut-down version of SQL, supporting only the most basic query functionality. It then added clean syntax for cursor operations, logic, and loops -- at that time no real standards existed for this side of SQL programming.

DAL was essentially a cut-down version of SQL, supporting only the most basic functionality, but adding clean syntax for cursor operations, logic, and loops -- at that time no real standards existed for this side of SQL programming. When sent a command the DAL interpreter broke down the statement and re-built it into subqueries for the underlying data sources. This translation took place on the server-side, unlike most similar tools, requiring a fairly expensive "adaptor" program of often dubious performance. This bit of architecture made DAL considerably less appealing than later systems like [[ODBC]], where the translation normally takes place on the client side and is typically "free".

On the client end, DAL was originally accessed directly through a "system extension", but DAL was later rolled into a single ODBC-like driver layer, the [[Data Access Manager]] (DAM). DAM was ODBC-like in concept, but did not include the SQL layers, it was strictly a system for sending opaque queries and receiving result sets. DAM also included the concept of a "query document" that allowed the DAL (or other) queries to be written in an authoring system and then easily used in any client application.

For much of the 1990s a direct-DAL database server was available on the Macintosh, '''Butler'''. However, like any server software on the "classic" MacOS, Butler was seriously hampered by the Mac's file system and could never really deliver the sort of performance the same server would have on [[Windows NT]] or [[Unix]].