Waterfall vs. Agile Methodology

Most software development projects apply either the Waterfall or Agile methodology. A development methodology is the procidure used by an engineering team in order to create a desired product. The Waterfall methodology represents the traditional approach, where the development process is conducted in a linear series of events. On its way toward the conclusion the progress flows continously through the phases of a project (analysis, design, development, testing, release) like a waterfall. The entire project is planned in advance. Agile is a more recently developed software development methodology, where the linear approach is replaced by an incremental, iterative one. Instead of planning the whole project in advance, Agile enables the adaption of requirements during the whole project. This artice provides an introduction of each methodology, a comparison and examples of use, in order to facilitate the decision whether Agile or Waterfall is more suitable for the next project.

Waterfall Methodology

The lifcycle model which is today known as traditional or Waterfall model was first described by Royce in 1970. It is called Waterfall model because of its sequential and down-flow characteristic where the phases analysis, design, implementation, testing and release are processed consecutively downwards. Each phase of the Waterfall model is processed in order without any overlapping and within a specified time period. Once a phase is completed there is no going back to a privious phase as it will be frozen.

Analysis

In this phase all the requirements and customer needs of the desired system or product are gatherd and recorded in detail in a specification document. This document will be used as input in the design and implementation phase. The requirements of the product should be clear before moving to the next phase as changes in requirement can not be adapted later in the process.

Design

The outcome of the design phase are a specified hardware and a virtual overview of the desired system or software.

Implementation

The actual development of the system starts in the implementation phase. The system is therefor divided in small sub units which are tested by the developers before forwarding them to the testing phase. A quality gate checklist helps to control if there is a deviation from the requirements, planned time-line and product scope.

Testing

In this phase the sub units are integrated to one working system which is tested regarding quality and functional aspects. The collected measures of performance are used for the decision whether the system is ready for the relase. In order to ensure that the outcome of the project meets the customers' requirements the tested system is reviewed according to a checklist.

Release

The product gets prepared for beeing released into the market or delivered to the customer (including installation instructions of the system for customers and user-guides). There is another quality gate in order to check if the final product meets the customer and quality requirements and wheter it is delivered in time.

Maintenance

After releasing the product in the customer environment there can occur problems in the products performance. Hence, the company must provide maintenace in order to solve this issues.

Pros

- All requirements are clearly documented before the development of the product starts

- Each phase is finished in a specified period of time before moving to the next phase

- Waterfall is simple to implement as it is a linear model

- The amount of resources needed for implementing the waterfall methodology is minimal

- Each phase follows appropriate documentation in order to ensure the quality development

Cons

- You cannot return to a privious phase. If the design phase fails the project might become very complicated in the implementation phase

- If a customer wants to change requirements of the product they cannot be implemented in the current development process

- Even small changes or errors in the finalized product might be very costly and cause a lot of problems

Agile Methodology

The Agile methodology uses an incremental, iterative approach instead of a linear and sequential one. Instead of extensive planning in advance it provides practices, tools and a culture that enable close collaboration of a team in a quick changing environment. During several successive iterations with a predetermined duration the team develops working products in order to get continous feedback from the customer. This procedure enables the team to improve the product with every iteration by adapting the requirements. Agile encourages selforganized cross-functional teams (incorpering planners, designers, developers and testers) with empowered members to create high quality outcomes. Scrum, Kanban, Lean, Extreme Programming (XP) and Feature Driven Development (FDD) are popular methodologies that follow the Agile values and principles. This values and principles which are explained in the Agile Manifesto published in 2001:

Agile Values

• Individuals and interactions over processes and tools
• Working software over comprehensive documentation
• Customer collaboration over contract negotiation
• Responding to change over following a plan

The Twelve Agile Principles

To be written...

Pros

- Changing requirements can be implemented at any phase of the process due to short development cycles

- A working product can be developed very quickly

- Continous improvement enables fast and high quality delivery

- Continious dialogue between the customer and the development team ensures immediate user feedback

- The Agile methodology attaches great importance to teamwork as it requires frequent communication and face-to-face interactions.

Cons

- Depends a lot on collaboration with the customer. Especially in long projects that is not allway possible

- Due to lack of documentation there is an increased dependence of interaction between developers

- Compared to linear and sequential models agile methodologies are more difficult to comprehand

- When used in large and complex projects it is difficult to estimate the costs and schedule

- Knowing that changes are possible the team could take hurried decisions without a proper analysis

Comparison of the Waterfall and the Agile Methodology

To be written: Detailed comparison and recommendaton when to use which model

Example of Use

The following examples demonstrate the different approaches of each methodology. The project goal is the development of a customer adress book.

Waterfall Model

Product Requirements

First, the Product Manager has to create a document of requirements:

• Enable user to create new contacts

• Enable user to see his contacts

• Enable user to import contacts from other applications

• Enable user to email his contacts from the adress book

• Enable user to add pictures to represent his contacts

The created document will comprise detailed requirements, user scenarios and potential layouts

Timeframe: 2 weeks

Analysis

Engineering team takes these requirements and analyzes them, asking questions as needed. Product manager updates documents as questions are resolved.

Timeframe: 1 week

Design Engineering team creates a design for functionality, including database design, mock-ups and workflows.

Timeframe: 3 weeks

Implementation Engineering team develops functionality and prepares it for testing.

Timeframe: 1 week

Testing Product team tests entire functionality.

Timeframe: 2 weeks

Release The product functionality is released.

TOTAL elapsed time: 9 weeks

Agile Model

Product Requirements

The product manager creates a document of requirements:

• Enable user to create new contacts

• Enable user to see his contacts

• Enable user to import contacts from other applications

• Enable user to email his contacts from the adress book

• Enable user to add pictures to represent his contacts

These requirements documents will be simple, and will include user scenarios. As each item is worked on, questions will arise, and there will be opportunities to discuss them as they occur. From this list, the requirements for the first iteration are chosen (starting with the highest priority items).

Timeframe: 1 week

Iteration Nr.1 The team works on the functionality to create new contacts and to view contacts. This includes the design, development and tes ting for these items. At the end of the iteration, the team demonstrates the functionality to the product manager, where he or she can provide feedback.

Timeframe: 2 weeks

Iteration Nr.2 Team works on the functionality to import contacts, to email and to add pictures to the contacts. This includes the design, development and testing for these items. At the end of the iteration, the team demonstrates the functionality to the product manager, where he or she can provide feedback.

Timeframe: 2 weeks

Iteration Nr.3 Team conducts a regression test and prepares to release the product.

Timeframe: 1 week

Release The product functionality is released.

Total elapsed time: 6 weeks

Note that if any changes to the requirements occur during this project, each iteration would adjust accordingly.