Day5

What is Business Logic Layer 2
 Services
 exposing business logic to outside system
 GPA system can provide graduation status for students
 Entities
 Students taking courses. Courses have schedules and
location.
 Courses are categorized by departments.
 Rules, Calculations
 Students can only register 20 units maximum per quarter
 CSE136 must be taken after CSE135, etc.
 Validation Cannot rely JavaScript for validation
 Is the social security # 9 digits?
 Is credit card all digits?

Business Layer Patterns
 Procedure Pattern 1980s

 Transcript Script pattern - A collection of procedures
(steps of execution).
 Table Module Pattern 1990s

 similar to transaction script but operations are
grouped by data (dataSet/dataTable)
 Object-based Pattern 21th century
 Interrelated & Interconnected objects.
 Active Record Pattern - record looks like data tables
from the database with additional methods()
 Domain Model Pattern - not ER diagrams, but OOD
diagrams

Procedure Pattern
 Map your business components directly onto
required user actions.
 Best suited for simple scenarios and unlikely
changing spec
 Simple and no start-up cost
 Can not handle large/complex specs
 As complexity grow, becomes more costly (not
easily extended)
 CSE 136 will NOT use this design pattern

Table Module Pattern
 Remember DataSet
in DAL (ADO.NET) Built-in in ASP.NET
 Series of transaction
grouped by Data
 Grouping the
info/table by how
data are related
 Good for quick
presentation display

Table Module Pattern 2
 What's wrong with this
Pattern?
 You must wait for SQL
stored procedures to
finish
 If SQL proc changes, it
changes the BL
structure
 remove a column
 changed a column
name
 You can't catch this
error through unit

Object-based Pattern - Active
Record Pattern
 Active Record Pattern is based on DataSet
design but create class object for each
DataTable.
 Duplication and quite a hassle
 Better than Table Module Pattern
 SQL Proc changes won't affect outcome
 One step closer to Object Oriented Design, but
not object-oriented yet

Object-based pattern - Active Record
Pattern ex

Object-Based Patterns - Domain Model
Pattern
 Domain Model is also known as Object-
Oriented Design
 Define the entities and the relationships &
flows between them
 Each Entity has data (variables) & behavior
(methods)
 Consider the issues of “coupling” and
“cohesion”. “Reuse”, “Maintainability”, and
“Extensibility”
 A diagram can be really large (divide &
conquer)
 More Object-oriented design using Design

Class Objects Design - steps
 Start with use case diagram
 Run thru activity diagram to identify entities
and high-level relationship
 Run thru sequence diagram again to identify
attributes and methods for each entities.
 You may skip this step for 136 to save time

Domain Model – class diagram
ex1

Database ER diagram is hidden away
From the Domain Model

How many tables to store student
info?

ex2

Review table in the database may have
a order_id, but in Domain Model, it is not
used.

ex3

Database ER diagram will have more
tables to stored these information
(vehicle, make, model, vendor, produc
t, location, back_order, etc).

ex4

Why use Design Patterns
 Provide a starting point for a solution
 Speed up productivity in a team
 Improves system and application design
 Carpenter: connector design pattern

Object-oriented Design Patterns
 Creational
 The creational patterns aim to separate a system from
how its objects are created, composed, and
represented
 They increase the system’s flexibility in terms of the
what, who, how, and when of object creation
 Structural
 Structural patterns are concerned with how classes
and objects are composed to form larger structures
 Behavioral
 Behavioral patterns identify common communication
patterns between objects
 They increase flexibility in carrying out this
communication

Creational Patterns
 Factory
 Singleton
 Prototype (skip)
 Abstract Factory (skip)
 Builder (skip)

Creational - Factory example
Logging C# example
available on class
homepage (136 project)

Polymorphism

Creational - Singleton Code

C# interview question

Structural Design Patterns
 Decorator
 Proxy
 Adapter
 Facade
 Bridge (skip)
 Composite (skip)
 Flyweight (skip)

Structural - Decorator example

Structural - Decorator

.NET libraries are
based on decorator
pattern

Behavioral Pattern
 Strategy
 Chain of Responsibility
 Iterator (skip - you have seen this in C#
lecture “enumerator”)
 Skip:
Observer, Command, Mediator, Memento, Stat
e, others…

Behavioral - Strategy example

Polymorphism

Behavioral - Strategy

Polymorphism

Client may come
From GUI

Behavioral - Chain example

Polymorphism

Behavioral - Chain

Polymorphism

Review question
 Why does domain model a better pattern at the
end?
 What are the three categories of OO design
pattern?
 Why are inheritance and polymorphism the
center of OO design pattern?
 Open/close principal, code flexibility.

Demo Code
 Business Logic Layer
 Domain Objects
 Error Logging implementation (factory pattern)
 Data Transfer Object

Your Assignment
 Due next Thursday
 Design and develop business layer based on
UML
 UML class diagram for Domain Object Model
 C# Domain Model classes
 C# Domain Business Logic
 Must use creational pattern for error-logging (log
to db or file based on app.config)
 Must use asynchronous call for error-logging
 Validations (regular expression – cover in day6)

 Developing test cases for your business layer

References
 .NET : Architecting Applications for the
Enterprise
 Design Patterns: Elements of Re-usable
Object-Oriented Software
 C# Design Patterns

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