The role of the data-access component
is central to the n-tier application model. In
the standard client/server model, the components
are divided into the following:
-
A client component, usually residing on local workstations and containing
a user interface and business rules.
-
A server component that implements data access.
In the standard three-tier model,
the components are as follows:
In an n-tier model, the components
are as follows:
-
A client component containing the user interface services
-
One or more business logic components that implement various broad areas of
business rules
-
One or more business data access components that mediate between the business
logic components and the data-services component
-
A data-services component that provides data to the dataaccess components
In the context of VB6 development,
a data-access component will typically be a COM
component exposing one or more data-aware classes,
as either of the following:
- An ActiveX EXE (an out-of-process component) running on a server
or
- An ActiveX DLL (an in-process component) running on a server under Microsoft
Transaction Server
An important consideration for
implementing individual data manipulation facilities
is the decision about whether to locate them
- With the data itself. In a SQL Server environment, for example, this would
take the form of stored procedures or triggers.
or
- In a separate data-access component, as discussed earlier.
