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Like Oracle's [[PL/SQL]] or Microsoft's [[Transact-SQL]], DAL is essentially an extended version of SQL supporting basic query functionality and adding clean syntax for cursor operations, logic, and loops.
When sent a command, early 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]], just like PL/SQL and Transact-SQL, but required a fairly expensive "adaptor" program of often dubious performance. This adaptor 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 ODBC approach is that, theoretically at least, more network bandwidth is used up to pull the "raw data" to the client machine for processing back into a standard format.
On the client end, DAL was originally accessed directly through a [[Extension (Mac OS)|system extension]] (named simply "DAL" in System 7), but it 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.
== Servers and clients ==
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