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Logical Architecture
The logical architecture looks at the application in terms of components. Physically, all of the tiers could be located on one computer, but logically each component of the application will be divided into separate files. The n-tiered approach will allow for all of these files to be separated into executable and dynamic link library (DLL) files which will allow for the simplification of the application as well as the maintenance and enhancements that will go along with it in the future.

Component Diagram

The following is a Component Diagram that was produced for my Visual Basic Virtual Placement Agency  project. 
 

 
Active Server Pages
  • The Active Server Pages (ASPs) are the interfaces for accessing the program over the web.  In my project, ASPs were created for the following:  a Login with a user name and password, a Home Page for the Virtual Placement Agency, Viewing a List and a Profile of Available Positions, Adding and Editing a Company Profile, Editing an Applicant Profile, and Applying for a Position (with a confirmation page).
The User Services Tier
  • The user services tier will logically be in the form of an executable file (.exe) and will be located on the user's computers. All of the users will be able to execute this file from their own computer location. In my project, this included the Login form, the Multiple Document Interface (MDI), the Companies, Positions, Applicants, and Skills forms, and the Place Applicant form.
The Business Services Tier
  • Also known as the business rules or the business logic, the business services tier will be set up as a dynamic link library file (.dll) and will be logically located on another computer even though physically it will be located on the user's computer. Because it is set up as a separate file, logically it could be anywhere. The business services tier works in the same manner no matter where it is logically located. The user services tier still has to communicate to the business services tier first in order to be able to get information passed back and forth from the data services tier. This includes the login, company, position, applicant, and skill objects, as well as a collection of skills.
The Data Services Tier
  • The data services tier will physically be located on another computer and will be set up as a dynamic link library file (.dll) This is where the actual database will be located. The Access database will be located within the data tier as well. It includes login, company, position, applicant, and skill data brokers as well as the data access object.

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The N-Tier Diagram

The diagram below refers to the logical software design of a “User Services” tier, a “Business Services” tier and a “Data Services” tier. The User Services tier is made up of the applications with which the user will directly interact. These can include custom applications, web browsers, report generators, etc. The Business Services tier contains the business logic of the application in one or more components. The Data Services tier consists of any data sources that need to be accessed by the application.
User Services Tier

Business Services Tier                   

Data Services Tier        

 

 

     




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