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Software Development Methodology
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Waterfall Methodology
All projects can be managed better when segmented into a hierarchy of
chunks such as phases, stages, activities, tasks and
steps. In system development projects, the simplist rendition of this is called the
"waterfall" methodology, as shown in the following figure:
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Software Process Models
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- he weekness of the Waterfall Model is at hand:
- It is very important to gather all possible requirements during the
first phase of requirements collection and analysis. If not all requirements are obtained at once the subsequent
phases will suffer from it. Reality is cruel. Usually only a part of the requirements is known at the beginning and
a good deal will be gathered during the complete development time. - Iterations are only meant to happen within the same phase or at best from the start of the subsequent phase back to the
previous phase. If the process is kept according to the school book this tends to shift the solution of problems into later
phases which eventually results in a bad system design. Instead of solving the root causes the tendency is to patch
problems with inadequate measures. - There may be a very big "Maintenance" phase at the end. The process only allows for a single run through the waterfall.
Eventually this could be only a first sample phase which means that the further development is squeezed into the last never
ending maintenance phase and virtually run without a proper process.
- It is very important to gather all possible requirements during the
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The disadvantages of the spiral model are that the risk assessment is rigidliy anchored in the process. First of all
it demands risk-assessment expertise to perform this task and secondly in some cases the risk assessment may not be
necessary in this detail. For completely new products the risk assessment makes sense. But I dare to say that the risks
for programming yet another book keeping package are well known and do not need a big assessment phase. Also if you think of the
multitude of carry over projects in many industries i.e. applying an already developed product to the needs of a new customer
by small changes, the risks are not a subject generating big headaches. Generally speaking the spiral model is not much
esteemed and not much used, although it has many advantaged and could have even more if the risk assessment phases would be tailored
down to the necessary amount.
» Waterfall? Spiral? Who cares? - DevChix - Blog Archive
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The waterfall and the spiral and other formal models such as the “surgeon” don’t model real-world software development very well because they ignore the impact of communication skills. The agile methods do not. XP, for example, sets up a formal channel of communication between the customer and the programmers. It also sets channels within the programming team via pair programming, nightly check-ins, and automated builds.
Project Lifecycle Models: How the differ and when to use them
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- Concept
- Requirements
- Architectural
design - Detailed
design - Coding
and development - Testing
and implementation - Minimizes
planning overhead since it can be done up front. - Structure
minimizes wasted effort, so it works well for technically
weak or inexperienced staff. - Inflexible
- Only
the final phase produces a non-documentation deliverable. - Backing
up to address mistakes is difficult.
Pure
Waterfall
This
is the classical system development model. It consists of discontinuous
phases:
Pure
Waterfall Summary
The pure waterfall performs well for products
with clearly understood requirements or when working with well
understood technical tools, architectures and infrastructures.
It's weaknesses frequently make it inadvisable when rapid development
is needed. In those cases, modified models may be more effective. -
- Determine
objectives, alternatives and constraints. - Identify
and resolve risks. - Evaluate
alternatives. - Develop
the deliverables for that iteration and verify that they are
correct. - Plan
the next iteration. - Commit
to an approach for the next iteration. - Early
iterations of the project are the cheapest, enabling the
highest risks to be addressed at the lowest total cost.
This ensures that as costs increase, risks decrease. - Each
iteration of the spiral can be tailored to suit the needs
of the project. - It
is complicated and requires attentive and knowledgeable
management to pull it off.
Spiral
The
spiral is a risk-reduction oriented model that breaks a software
project up into mini-projects, each addressing one or more major
risks. After major risks have been addressed, the spiral model terminates
as a waterfall model. Spiral iterations involve six steps:
Spiral
Summary
For projects with risky elements, it's beneficial
to run a series of risk-reduction iterations which can be followed
by a waterfall or other non-risk-based lifecycle. - Determine
What is the diff. Between Waterfall and Spiral model?
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The waterfall model the process goes to the next step after
completion of the previous step as first requirement then
design then coding then implementation then maintenance but
here is no end user feedback taken to consideration any
change in SRS will result to start work fro first step and
goes step by step again.
But in case of Spiral model for each and every step there
is testing for that step carry on simultaneously after
finishing that step so that it will easy to recover any
error and fix it there. In this model we don?t have to
start work from beginning -
# 2In the water fall model the process flows from top to
bottom like a flow of water . But any new changes can not
be incorporated in the middle of the project development.
Whereas the spiral model is best suted for projects
associated with risks.
The Waterfall Model Explained
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The Waterfall Model Explained
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Waterfall approach was first Process Model to be introduced and followed widely in Software Engineering to ensure success of the project. In "The Waterfall" approach, the whole process of software development is divided into separate process phases. The phases in Waterfall model are: Requirement Specifications phase, Software Design, Implementation and Testing & Maintenance. All these phases are cascaded to each other so that second phase is started as and when defined set of goals are achieved for first phase and it is signed off, so the name "Waterfall Model"
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Spiral Model - A New Approach Towards Software Development
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The Waterfall model is the most simple and widely accepted/followed software development model, but like any other system, Waterfall model does have its own pros and cons. Spiral Model for software development was designed in order to overcome the disadvantages of the Waterfall Model.
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Understanding the pros and cons of the Waterfall Model of software development
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Overview
Waterfall development isn't new -- it's been around since
1970 -- but most developers still only have a vague idea of what it means.
Essentially, it's a framework for software development in which development
proceeds sequentially through a series of phases, starting with system
requirements analysis and leading up to product release and maintenance.
Feedback loops exist between each phase, so that as new information is
uncovered or problems are discovered, it is possible to "go back" a
phase and make appropriate modification. Progress "flows" from one
stage to the next, much like the waterfall that gives the model its name. -
six distinct phases, described below:
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Software Development Today
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Many years ago in 1970, Winston Royce wrote an article where he described (and warned about) the use of the one-pass waterfall ("waterfall" for short). In that article Royce states that if the waterfall was to be used, it should be a "multi-pass" waterfall with many feedback cycles between the different phases, where when you pass through a phase (be it requirements, design or any of the other 7 phases Royce defined in his paper) you learn more about the previous phase and should include that feedback by re-iterating the previous phase.
Later, in 1988, Barry Bohem, also known for his work in the domain of Risk Management came up with the Spiral model of development. This process improvement wave introduced the concept that you do a little bit of everything as you go (e.g. early prototyping), and you repeat often. There was little talk of releasing working software often and interacting with customers, but this was a big push towards the "incremental" process model.
Image:Overview of a three-tier application.png - Wikipedia, the free encyclopedia
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No higher resolution available.
Overview_of_a_three-tier_application.png (596 × 536 pixels, file size: 76 KB, MIME type: image/png)
Multitier architecture - Wikipedia, the free encyclopedia
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- A front end Web server serving static content
- A middle dynamic content processing and generation level Application server, for example Java EE platform.
- A back end Database, comprising both data sets and the Database management system or RDBMS software that manages and provides access to the data.
Web Development usage
In the Web development field, three-tier is often used to refer to Websites, commonly Electronic commerce websites, which are built using three tiers:
Three Tier Architecture (Linux journal) [1]
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