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Application Logic

Database architectures can be distinguished by examining the way application logic is distributed throughout the system.  Application logic consists of three components: Presentation Logic, Processing Logic, and Storage Logic. 

The presentation logic component is responsible for formatting and presenting data on the user's screen The processing logic component handlesdata processing logic, business rules logic, and data management logic.  Finally, the storage logic component is responsible for the storage and retrieval from actual devices such as a hard drive or RAM.By determining which tier(s) these components are processed on we can get a good idea of what type of architecture and subtype we are dealing with.

One Tier Architectures

Imagine a person ona desktop computer who uses Microsoft Access to load up a list of personal addresses and phone numbers that he or she has saved in MS Windows' “My Documents” folder.  This is an example of a one-tierdatabase architecture.  The program (Microsoft Access) runs on the user's local machine, and references a file that is stored on that machine's hard drive, thus using a single physical resource toaccess and process information.

Another example of a one-tier architecture is a file server architecture.  In this scenario, a workgroup database is stored in a shared location on a single machine.Workgroup members use a software package such as Microsoft Access to load the data and then process it on their local machine.  In this case, the data may be shared among different users, but all ofthe processing occurs on the local machine.  Essentially, the file-server is just an extra hard drive from which to retrieve files.

Yet another way one-tier architectures have appeared is in that ofmainframe computing.  In this outdated system, large machines provide directly connected unintelligent terminals with the means necessary to access, view and manipulate data.  Even though this is...