info415 approaches to system development: part 2

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”