Datasheet

Displaying Data on the Web
17
In the recent past, most applications communicated with data stores through the software objects
provided by ADO, which made use of the lower-level technologies OLE DB and ODBC. In order for
this to happen, ADO (and its replacement, ADO.NET) rely on a database conforming to an underlying
set of standards. A significant difference between old and new is that ADO.NET has a less demanding,
more flexible set of rules, allowing for a greater variety of data sources.
To allow applications to make connections to their databases, database vendors have to implement
some common sets of functionality (interfaces) that have been devised for this purpose. One such
interface is the highly successful ODBC, which is still supported by the vast majority of databases you'll
come across. Another technology, OLE DB, was designed as the successor to ODBC, and was the
cornerstone of Microsoft's Universal Data Access strategy. It too has become highly successful, and has
gained broad support.
The diagram below shows a simplified version of how the various pre-.NET data access technologies
connect to databases – and even in this diagram you can see that it was all getting a bit complicated! As
well as ADO, OLE DB, and ODBC, technologies like RDO and DAO were getting involved too:
SQL ServerOracle
SQL-Compatible data-stores
Exchange
Other data-stores
OLE DB
ADO RDO
ODBC
Application
DAO
Application
Data Access Layer
Database