Business Layer

Transaction Script

• Organizes business logic by procedures where each procedure handles a single request from the presentation. –Martin Fowler
• Benefits: Simple to implement.
• Negatives: - Danger of code duplication. - Spaghetti code. - A number of transactions accomplishing very similar tasks. - Hard to refactor.
• Technology:
  • ADO.NET

Table Module

• A single instance that handles the business logic for all rows in a database table or view.–Martin Fowler
• Benefits: Good visual studio support, easy databinding, database agnostic (choose provider), provides disconnect data modification.
• Negatives: Database centric API.
• Technology: .NET DataSet, DataTable, DataRow and DataAdapter structures (typed).

Active Record

• Focuses on classes representing records in a table (row based view) whereas Table Module focuses on entire tables. But still considered a form of Table Module.
• The object incorporates both data (column values) and behaviour (methods).
• i.e an Order class for an Orders table, with a static GetOrders() method that returns a collection of orders, Insert, Delete, Update methods etc.
• Benefits: Simplicity, vendor support.
• Negatives: Not as efficient as straight DataSets. Gets complex if the problem domain grows away from the database design.
• Technology: LINQ-to-SQL and Castle ActiveRecord (built on top of NHibernate, simpler).

Domain Model

• An object model of the domain that incorporates both behavior and data.–Martin Fowler
• Domain driven design as opposed to data centric design.
• Completely flexible to model the domain in any way you see fit through object oriented practices, "A web of interconnected objects".
• A big brother to Active Record and is totally independent of the database.
• Benefits: Easier maintainability, less code duplication, best way to model a complex system, persistence ignorance with plain old common objects (POCO).
• Negatives: More work upfront, requires an O/R mapper.
• Technology: NHibernate, Microsoft Entity Framework or NoSQL solutions such as MongoDB.