In many instances, the logical layer is a physical layer, but it is not
always true. Let me give you an example:
1. You build a large EXE project. Inside the project, you build individual
classes to encapsulate your business objects, as well as classes for data
access. Logically, you have three layers (presentation, business and data),
but physically, you only have one: MyApp.exe.
2. You start selling MyApp and find that some of the data needs to reside on
your server, as it is aggregate data that makes your app have market value.
You move the data classes to a data server. You now have two physical layers,
but still three logical.
3. You experience huge growth at MyApp corporation and you now need to move
the data access classes off of your SQL Server, to an application server. You
now have three physical layers and three logical layers, but the logical data
layer now spans two physical layers.
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Gregory A. Beamer
MVP; MCP: +I, SE, SD, DBA
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Think Outside the Box!
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