Data Access Language: Difference between revisions

Revision as of 13:44, 21 May 2005

Revision as of 13:56, 21 May 2005

Line 3:

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.

Several "plug-in"s for DAL werewas provided,accessed including one forthrough Apple's own ODBC-like driver layer, as[[Data wellAccess asManager]]. aOne directof plug-inthe more common uses forwas [[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 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.