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SYS366

Lecture 1:

Introduction to Systems

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What is Software Development?

Software Development implies developing some software – but it does not involve simply coding programs

Software is developed to turn manual processes into automated processes or to improve/enhance existing automated processes.

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What does this have to do with Systems?

Software Development entails understanding the problem to be solved, understanding how a business operates and understanding that the solution to be developed will be of value to the business (First ½ of SYS366)

The Systems stream of courses provide the knowledge of the steps that need to be followed to successfully create a software solution from the inception of the idea to a working, fully operational system. This collection of steps is called the Systems Development Life Cycle.

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What is a system?

A combination of hardware and developed software that create the software solution that meets the needs of a business.

A collection of inter-related components that collect, process, store and provide as output the information needed to complete business tasks.

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What is a system?

Characteristics of a system*– It exists in an environment– It is separated from its environment by some kind of

boundary– It has inputs and outputs which come from, or are sent to the

environment– It has interfaces (allows communication between two

systems)– It can have sub-systems (which are also systems)– It has a control mechanism

*Object-Oriented Systems Analysis & Design using UML, 1999 pages 5-6

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What is a system?

What the system does

System Boundary

Inputs Outputs

Control

How the system is controlled

FeedbackFeed-forward

*Object-Oriented Systems Analysis & Design using UML, 1999 pages 5-6

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Need for Software Development:

– Environments are rapidly changing– New technologies are frequently introduced– Companies merge and need to combine their

systems– Government legislation

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Software Development Typical Solutions

Developed in-house Turnkey Off-the shelf Contracted out

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Software Development Lifecycle (SDLC)

Software Development Projects are developed according to a definite methodology called the SDLC

• organizes the activities of a project•Interactive and Incremental•followed by anyone involved in software development

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What is a methodology?

Comprehensive guidelines to follow for completing every SDLC activity

Collection of techniques Examples: Structured (Traditional), Object-oriented

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Software Development Methodologies

Structured– Worked well for centralized processing applications and

procedural languages Object Oriented

– Works for GUI and web solutions– OO languages: C++, Java

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StructuredSoftware Development Methodology

Based on the functions that a system needs to perform Development is rigid: does not allow for changes easily

without significant impact to a project deadline Components do not tend to be reusable: solution

developed is for a specific set of functions (which usually aren’t shared)

Uses Data Flow Diagrams (the flow of data through a system) and Entity Relationship Diagrams (the data the system is going to use)

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Object-oriented Software Development Methodology

Fundamentally different from traditional software development

Object-oriented approach– Real world objects are modeled by corresponding

programming objects. Objects have state, behaviour and identity.

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Object OrientedSoftware Development Methodology

Based on the interaction that happens between ‘objects’

Does still consider the functions the system needs to perform however

Allows for reusability or sharing of code (a dialogue box construct is the same across applications)

Reduces the development time for an application Focuses on object technology such as multimedia

systems

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The Phases of the SDLC: Software (or Systems) Development Life Cycle

The Phases of the SDLC for both the Structured and the OO methodologies are similar

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SDLC: Software (or Systems) Development Life Cycle

Project Planning Phase Analysis Phase: understanding business needs Design Phase: conceptualizing computer-system

solutions Implementation Phase: coding, testing and installation Support Phase

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What is a technique?

Collection of guidelines that help the Developer complete a system development activity or task within a phase

Step-by-step instructions General advice

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Techniques

Techniques are used to complete specific system development activities– Project planning techniques– Systems analysis techniques– Systems design techniques– System construction and implementation techniques– System support techniques

Example: Rational Unified Process

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Models

Representation of an important aspect of the real world

examples– Diagrams and charts– Project planning aids– Business Use case Models and System Use Case

Models drawn in Rational Rose

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Why the move to Object-oriented Methodology?

– Software Development is too expensive Poor Quality Late Delivery Poor Productivity Too much person-power needed Fragile systems Legacy Systems User Interfaces not state of the art

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Why the move to Object-oriented Methodology?

– Software Developers are being asked to Develop more sophisticated systems Tackle more complex systems Produce more reliable and malleable systems Shorten the delivery cycle Reduce costs

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Software Development

Some common causes for Failure:– Deadlines that cannot be met– Budgets that have been exceeded– Solutions that don’t work– Systems too complex to maintain– Customer’s requirements not fully understood or

captured correctly– Customers continually change their requirements– Customers are not committed to the project

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How does the Object-oriented SDLC help to overcome these problems in Software Development?

The system under development is refined and transformed through analysis, design, code and test phases – details are added in successive iterations (changes and improvements are introduced as needed) and incremental releases of software modules are delivered.

System design – developing information systems using UML by Leszek A. Maciaszek (page 5, 2001)

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Iterative Nature of the Software Development Life Cycle

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SDLC Variations

Developers encounter many variations of SDLC in practice. Based on:

– Phases– Iteration– Emphasis on people– Speed of development

BUT you have to understand the basic methodology before you can vary it