Data Access Language: Difference between revisions

Revision as of 02:42, 7 September 2005

Revision as of 14:08, 29 October 2005

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'''Data Access Language''', or simply '''DAL''', was a [[SQL]]-like language parser released by [[Apple Computer]] in 1990 to provide unified [[client/server]] access to [[database management system]]s. It was known for poor performance and high costs, something Apple did little to address over it's short lifetime.

==History==

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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.

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 included for free with the database engine. The downside to the later approach is that more network bandwidth is used up to pull the "raw data" to the client machine for processing.

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 single-user [[file system]] and [[multitasking]] and could never really deliver the sort of performance the same server would have on [[Windows NT]] or [[Unix]].

One of the more common clients for DAM was [[HyperCard]]. The combination of HyperCard and DAL presented a serious challenge to existing vendors who could offer nothing with a GUI. Apple gave a series of demos of HyperCard/DAL, and soon [[Oracle]] purchased a HyperCard-clone, PLUS from [[Spinnaker Software]], to produce [[Oracle Card]].