N-Tier Architecture: The Business Rules Layer

Business Rules Layer in N-Tier Architectures

The Business Rules Layer in an N-Tier architecture is that layer that contains the Business logic and / or Business rules of the application. Reserving a separate layer strictly for Business logic in an N-Tier architecture is a major advantage, in that any changes that need to be made to Business rules can be made here without having any effect on other applications.

Assuming that the interface among the different layers stays the same, changes that are made to the functionality / processing logic in the Business Rules Layer can be readily made without having any affect on the others. In the past, many client server applications failed to implement because the changing of the Business rules or logic was such a difficult process.

The Business Rules Layer in an N-Tier system is where all the application’s brainpower resides. It contains data manipulation, Business rules, and all the other important components that your Business needs to survive. If you happen to be creating a search engine and have the need to weight or rate every matching item according to some sort of custom criteria – let us say the number of times a keyword was found in the result of a quality rating – then the Business rules layer should be placed on this layer. The Business Logic Layer does not know anything about HTML – it does not out put HTML, either.

Nor does the Business Logic Layer care about things like SQL or ADO. The Business Logic Layer should not contain any code that enables it to access the database. Such tasks should be assigned to corresponding layers above and below it.

Business Rules Layer in Three Tier Architectures

While N-Tier architecture typically refers to three or more levels, the fact is that three level architectures are the most common. The three levels consist of the user interface, the Business rules layer, and the data. It used to be, in classic ASP, that the user interface level would consist of HTML tags alongside VBScript, which was used to construct the page layout. The data level would be a database, such as SQL server.

The Business rules layer was oftentimes underused in a really horrible fashion – with detrimental results. A lot of times the Business rules layer in Classic ASP Web applications would not even have any Business rules in it. It would merely consist of a stored procedure wrapped inside Visual Basic pass through components.

The only real reason why Classic ASP developers would even bother with VB components was due to the performance advantage of leveraging compiled code. It is rather obvious that the term “object oriented” was just an object of lip service throughout this Classic ASP period.