INFO415
Approaches to System Development:Part 2
Two Approaches to System Development• Traditional Structured Approach vs. Object Oriented
Approach• Both are widely used today. • Older, established organizations: lean toward the
traditional approach• Newer organizations, or those with heavy emphasis
on the Web, moving toward Object Oriented approach
• Approaches are not mutually exclusive!!
Structured Approach• Structured system development has 3 components
• Structured programming• Structured design• Structured analysis
• Collectively referred to as structured analysis and design technique (SADT)
• The approach evolved over many years (60s to 80s) in order above. Why this order?
Structured Programming
• Improves computer program quality
• Allows other programmers to easily read and modify the code
• Each program module has one beginning and one ending
• Three programming constructs
Three Structured Programming Constructs
Top-Down Programming• Divides complex programs into hierarchy of modules
• Module at top controls execution by “calling” lower level modules
• Modular programming • Similar to top-down programming • One program calls others to work as single system
Structured Design• Developed in response to
increasing complexity of applications
• Developed to provide guidelines • What the set of programs should be• What each program should
accomplish• How programs should be organized
into a hierarchy
• Main principles of program modules• Loosely coupled - independent• Highly cohesive - one clear task
Structured Analysis• Emerged in the 1980s• Helps developer define what the system needs to do
(processing requirements)• Defines:
• Events that trigger system functions • System functions• Data to store and use• Inputs and outputs• How functions work together
• Data Flow Diagrams (DFDs) and Entity Relationship Diagrams (ERDs) are mostly important and commonly used models from Structured Analysis
Data Flow Diagrams• Data Flow Diagrams
(DFDs) model what the system needs to do and what data must be stored
• Shows inputs, processes, outputs and data stores
• Start at high level and drill down – “functional decomposition”
Entity Relationship Diagrams• Entity Relationship Diagram (ERD) models the data that must be
maintained within the system.• Entities: ‘things’ that the system must maintain information
about• Relationships: how the entities are related to each other• Entities correspond to data stores on DFD diagrams
What is common between these diagrams?
Weaknesses of Structured Approach• Evolved over time – many variations, lack of cohesion
between models• Data more of an afterthought – focus is on function• Some issues from transitioning from analysis to design
– different set of models• In response, Information Engineering (IE) approach
has emerged
Information Engineering Approach• System development methodology that focuses on
strategic planning, data modeling, and automated tools
• More rigorous and complete than the structured approach
• Basic idea: data/information is a corporate resource that does not change very quickly. Focus on data first; processes that use data second
• Models generated are similar to the structured approach.
Structured Approach vs Information EngineeringThe structured approach is a model-driven, process-centered but data sensitive technique.
Information engineering (IE) is a model-driven and data-centered, but process-sensitive technique.
Object-Oriented Approach• Views information systems as collections of interacting objects
that work together to accomplish tasks• Objects - things in the computer system that can respond to
messages• An object is a type of thing (person, order, product, button or
pull-down menu)• No processes, programs, data entities, or files• Object-oriented languages include C++ and Java• Object Oriented approach consists of:
• Object-oriented analysis• Object-oriented design• Object-oriented programming
Object-Oriented Approach to Systems
Object-Oriented Analysis• Object-oriented analysis
• Defines all of the types of objects that do the work of the system
• Shows how objects interact• Class: A collection of
similar objects (Customer)• Class Diagram:
• Produced during object-oriented analysis to show all classes of objects in the system and how they relate to each other.
Object-Oriented Design and Programming
• Object Oriented Design:• Defines all additional object types needed to communicate
with people and devices in the system• Refines each type of object for implementation within a
specific language (e.g., Java or C++)• Object-oriented Programming:
• Writing statements in programming language to define what each object does
Benefits of the Object-Oriented Approach• Naturalness• Reuse• Example
Traditional vs. Object-Oriented Approach• As part of a project, defined the following
requirements related to customer information:• The information we need to maintain for customer includes:
name, address, and credit limit and current A/R balance• We need the ability to add new customers over time• We need to be able to delete inactive customers from the
system• We need to be able to raise/lower customer credit limits
over time.• We need to be able to view current information about the
customer on demand.
Traditional vs. Object Oriented Approach
Traditional Approach (structured/IE)
CustomerTable
Customer IDName
AddressCredit Limit
Current Balance
AddNew
CustomerProgram
UpdateCredit Limit
Program
DeleteCustomerProgram
QueryCustomerProgram
Object Oriented Approach
“table”“programs”
“object”
Customer IDName
AddressCredit Limit
Current Balance
createCustfindCust
updateCustdeleteCust
Customer
“methods”
