In this explanation ‘thin client’ means web-application.

Application layer or presentation layer:

Internet explorer or browser is the application layer client software that handles the http requests for the user who is using thin client.

What the presentation layer does:1. It accesses the server software of thin client (ie the server.dll files) to the user’s interface that is the web

browser through IE. It basically presents the application to the user who wants to use thin client2. Application layer uses the http or https protocol to handle the requests from the user to the server and

then resend the result back from the server to the user.Example:User enters a login name and pwd and clicks on loginPresentation layer handles this http request by verifying this login name and pwd by sending this request via the API’s to the database via the database engineOnce the API which is in the business logic layer verifies this login is correct, it will resend the serviced http request to the browserHence the user will be able to login

3. if the application does not support the presentation layer then the user cannot use a web browser to talk to the application

4. presentation layer basically handles the data representationExample: the pwd is stored in an encoded format in the database. That is the reason why a pwd appears in asterisk when a user enters his pwdExample: the RTF data might be stored in a non readable format in the database, but to the user in the presentation layer it appears as a readable text

5. sql management studio, internet explorer, db visualizer, crystal reports - these are some examples of presentation layer softwares.

Business logic layer:

This basically deals with how the application will behave when a user is performing some action. The main logic behind how the application behaves is coded in this business logic layer.For example: if u want the administrator to add a new user only with a min of 5 characters length login name then the API associated with this new ‘user adding’ functionality is coded in this business logic layer only

Example: this is the layer which will service the user requests coming form the presentation layer and then processing the request as per the API functions that are built in the business logic layer. Like for example if a user is trying to add a new record for which he has no permission, then it is the business login layer which will determine if the user really has permission to add a record or no.

What ever you do in the application, the main logic for the behavior of the application is determined by the business login layer

Another example:When you search for records in the thin client, the logic behind how to search the records is coded in this business login layer only.

Another example: suppose I want to add rules, lists, and permissions on a table. Then all this logic is defined in this layer.

Our schema wizard rules, lists, security, schema options, CDX, external tables are all part of the business logic layer.

LDAP, windows authentication, RDB users, by pass security – all this work because of the business logic layer only

Without business logic layer no application can work

Database layer:

Requests coming from presentation layer go to business logic layer via the API or inbuilt functions in the code.Now the business logic layer will talk to the database layer by validating the data entered by the user with the data already stored in the database layer.

For example: a user adds a record. The business logic layer will process this request and then send a database create request to the database layer via the database engine to add this record in the database.

Example: if a user wants to run a report, then the business logic layer will send the database query request like select * from account; to the database layer. Then the business logic layer will send the records of the query to the presentation layer to present it to the user.

Basically database layer is the database server of our application. The database server handles the requests of the presentation and the business logic layer via the database engine.

If the schema wizard is adding a new table, then it the database layer which is doing the job of adding the new table.

DSN connection is used by Saratoga to talk to the database layer.

Note:Application server can expose the business logic layer API’s to the developers, so that the developers can build the application like how ever they want.This is one of the main features of the application server like IIS.