Data Access Language: Difference between revisions

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== History ==

DAL started as a 3rd-party product, '''CL/1''' (''Connectivity Language One''), from a small vendor, Network Innovations. Apple purchased the company in 1988,<ref>[https://books.google.com/books?id=jspVAAAAMAA "Apple Acquires Network Innovations"]{{Dead link|date=January 2024 |bot=InternetArchiveBot |fix-attempted=yes }}, ''Wheels for the Mind'', Boston College, 1988</ref> during a time that client/server databases were becoming a hot issue in the industry. They released their first version of the re-branded software in 1989, for [[MVS]], and followed with other versions over the next year or so.

DAL suffered from most Apple problems of the early 1990s, notably an alternating level of support in which Apple would aggressively promote the product and then ignore it. Throughout, the company struggled with promoting the system as a cross-platform standard, or as a Mac-only technology.<ref>Jeff Moad, [https://books.google.com/books?id=uRlJAQAAIAAJ "Apple Says Yes to SQL"], ''Datamation'', 1990</ref> DAL's release was also coincident with Apple's fall from grace in the business world, and not coincidentally with [[Microsoft]]'s [[ODBC]] efforts.

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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 ==