Data Access Language: Difference between revisions

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'''Data Access Language for the Macintosh''', or simply '''DAL''', was a [[SQL]]-like language parserand [[application programming interface]] released by [[Apple Computer]] in the early 1990s1990 to provide unified [[client/server]] access to [[database management system]]s. AppleIt purchasedwas theknown systemfor frompoor aperformance smalland vendorhigh costs, whosomething calledApple did little to address over its short lifetime, before it '''CL/1'''was (''commandsold languageoff 1'')in prior1994. toDAL is used as the purchasenative SQL dialect of the [[PrimeBase]] SQL server, as well as the now-defunct [[Butler SQL]].

== History ==

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. When sent a command the DAL interpreter broke down the statement and re-built it into subqueries for the underlying data sources. For instance, DAL users could write a single SQL query that would be applied to two physically separate databases, DAL would then produce smaller subqueries for each server, and combine the results on the way back. This is similar in nature to how [[Microsoft Access]] works, but provided at a system-wide level. In this respect DAL is much higher level in concept than systems like [[ODBC]] or [[JDBC]], which essentially define the "pipe" to the data source and little more.

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.

Several "plug-in"s for DAL were provided, including one for Apple's ODBC-like layer as well as a direct plug-in for [[HyperCard]]. The combination of HyperCard and DAL presented a serious challenge to existing vendors who could offer nothing with a GUI, and soon [[Oracle]] purchased a HyperCard-clone to produce Oracle Card.

DAL appears to have seen little use, and eventually Apple sold it to Independence Technologies in 1994, during a sell-off of a number of "high-end" packages such as their [[X.400]] server and an [[Systems Network Architecture|SNA]] client.<ref>[http://www.xcbronline.com/news/apple_divests_data_access_language_snaps_takes_bedrock "Apple Divests Data Access Language, SNAps, take Bedrock"]{{Dead link|date=July 2019 |bot=InternetArchiveBot |fix-attempted=yes }}, ''Computer Business Review'', 26 January 1994</ref> Independence Technologies was a [[middleware]] vendor, better known as a major reseller of the [[Tuxedo (software)|Tuxedo]] product for [[Unix]]. In 1995 [[BEA Systems]] bought the company, and in turn sold it to [[UniPrise Systems]] in late 1996. No releases took place during this period.

DAL suffered from most Apple problems of the early 1990s, notably a alternating level of support in which Apple would present the product and then ignore it. DAL's release was also coincident with Apple's fall from grace in the business world, and not coincidentially with [[Microsoft]]'s ODBC efforts (while almost certainly led to Apple's efforts). It appears to have seen little use, and the product was eventually sold off again in the mid-90s, never to be seen again.

== Description ==

[[Category:Failed Apple initiatives]]

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 ==

SeveralOne "plug-in"sof forthe DAL were provided,more includingcommon oneclients for Apple'sDAM ODBC-like layer as well as a direct plug-in forwas [[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, [[WinPlus|PLUS]] from [[Spinnaker Software]], to produce [[Oracle Card]].

For much of the 1990s a direct-DAL database server was available on the Macintosh, [[Butler SQL]]. However, like any server software on the "classic" Mac OS, Butler was seriously hampered by the Mac's single-user [[file system]] and limited [[Computer multitasking|multitasking]] and could never really deliver the sort of performance the same server would have on [[Windows NT]] or [[Unix]].

The [[PrimeBase]] division of German software developer SNAP Innovation GmbH continues to support DAL in their cross platform SQL database server (originally known as P.INK SQL). Their extended version of DAL is called PrimeBaseTalk (PBT) and is fully backward compatible with DAL. Their architecture does not include Data Access Manager and the resulting performance gains are considerable.

IBM made available a DAL Server for the [[IBM i|AS/400 platform]] in 1995.<ref>[https://www.ibm.com/common/ssi/cgi-bin/ssialias?infotype=DD&subtype=SM&htmlfid=897/ENUS5733-CSR IBM AS/400 Client Series End User Products], IBM</ref>

== References ==

{{reflist}}

[[Category:Macintosh operating systems development]]

[[Category:Classic Mac OS programming tools]]