Data Access Language: Difference between revisions

Revision as of 12:29, 25 May 2005

Revision as of 12:36, 25 May 2005

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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 dubious performance. This bit of architechture 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, [[Data Access Manager]] (DAM). OneDAM ofwas ODBC-like in concept, but did not include the moreSQL commonlayers, clientsit was [[HyperCard]].strictly Thea combinationsystem offor HyperCardsending opaque queries and DALreceiving presentedresult asets. seriousDAM challengealso toincluded existingthe vendorsconcept whoof coulda offer"query nothingdocument" withthat aallowed GUI,the andDAL soon(or [[Oracle]]other) purchasedqueries ato HyperCard-clone,be PLUSwritten fromin [[Spinnakeran Software]],authoring tosystem and then easily used in produceany [[Oracleclient Card]]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, Bulter 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]].

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]].

[[Category:Failed Apple initiatives]]