Data Access Language: Difference between revisions

Revision as of 20:17, 2 August 2005

Revision as of 12:45, 9 August 2005

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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.

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.