Data Access Language: Difference between revisions

Revision as of 16:47, 26 May 2006

Revision as of 00:22, 22 November 2006

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==Description==

Like Oracle's [[PL/SQL]] or Microsoft's [[Transact-SQL]], DAL wasis essentially aan cut-downextended version of SQL, supporting only the most basic query functionality. Itbut then addedadding clean syntax for cursor operations, logic, and loops. --A atnumber that timeof novendor realspecific standards existedexist for this side of SQL programming.

When sent a command, theearly versions of Apple's 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, unlikejust mostlike similarPL/SQL toolsand Transact-SQL, requiringbut required a fairly expensive "adaptor" program of often dubious performance. This bit of architectureadaptor 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 laterODBC 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.

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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 Corporation]] purchased a HyperCard-clone, PLUS from [[Spinnaker Software]], to produce [[Oracle Card]].

The PrimeBase division of German software developer SNAP Innovation GmbH continues to support DAL in their cross platform SQL database server. Their extended version of DAL is called PrimebaseTalk and is fully backward compatible with DAL. Their architecture does not include Data Access Manager and the resulting performance gains are considerable.

[[Category:Mac OS development]]