Quality Function Deployment (QFD) in Software Quality

Quality Function Deployment (QFD) is process or set of tools used to define the customer requirements for product and convert those requirements into engineering specifications and plans such that the customer requirements for that product are satisfied.

• QFD was developed in late 1960s by Japanese Planning Specialist named Yoji Akao.
• QFD aims at translating Voice of Customer into measurable and detailed design targets and then drives them from the assembly level down through sub-assembly level, component level, and production process levels.
• QFD helps to achieve structured planning of product by enabling development team to clearly specify customer needs and expectations of product and then evaluate each part of product systematically.

Key steps in QFD :

1. Product planning :
   • Translating what customer wants or needs into set of prioritized design requirements.
   • Prioritized design requirements describe looks/design of product.
   • Involves benchmarking – comparing product’s performance with competitor’s products.
   • Setting targets for improvements and for achieving competitive edge.
2. Part Planning :
   • Translating product requirement specifications into part of characteristics.
   • For example, if requirement is that product should be portable, then characteristics could be light-weight, small size, compact, etc.
3. Process Planning :
   • Translating part characteristics into an effective and efficient process.
   • The ability to deliver six sigma quality should be maximized.
4. Production Planning :
   • Translating process into manufacturing or service delivery methods.
   • In this step too, ability to deliver six sigma quality should be improved.

Benefits of QFD :

1. Customer-focused –
   Very first step of QFD is marked by understanding and collecting all user requirements and expectations of product. The company does not focus on what they think customer wants, instead, they ask customers and focus on requirements and expectations put forward by them.
2. Voice of Customer Competitor Analysis –
   House of Quality is significant tool that is used to compare voice of customer with design specifications.
3. Structure and Documentation –
   Tools used in Quality Function Deployment are very well structured for capturing decisions made and lessons learned during development of product. This documentation can assist in development of future products.
4. Low Development Cost –
   Since QFD focuses and pays close attention to customer requirements and expectations in initial steps itself, so the chances of late design changes or modifications are highly reduced, thereby resulting in low product development cost.
5. Shorter Development Time –
   QFD process prevents wastage of time and resources as enough emphasis is made on customer needs and wants for the product. Since customer requirements are understood and developed in right way, so any development of non-value-added features or unnecessary functions is avoided, resulting in no time waste of product development team.

A QFD Tool – House Of Quality (HOQ) :
House of Quality or HOQ is conceptual map or matrix that provides an understanding of how customer requirements (WHATs) are related to various technical descriptors or design parameters (HOWs) and their priority levels. House of Quality is also known as Quality Matrix. The matrix gets its name from fact that it represents the shape of house.

A House of Quality has the following parts :

1. WHATs –
   Customer requirements and needs are listed.
2. Importance Factor –
   The team rates each of customer requirements (WHATs) on scale of 1 to 5 based on their level of importance to the customer. Here, 1 denotes lowest level and 5 denotes highest level of importance to customer.
3. HOWs or Ceiling –
   It comprises design features, technical descriptors and specifications of product aligned with customer requirements.
4. Body –
   HOWs are ranked on basis of their correlation of satisfying each of listed WHATs. Body Ranking System used is set of symbols used to show Strong, Moderate, Weak or No correlation between HOWs and WHATs. Also, each of symbols represents numerical value.
5. Roof –
   The roof indicates how design requirements(HOWs) are related to each other. Roof Ranking System uses set of symbols to represent different types of interactions – Strong Positive, Positive, None, Negative or Strong Negative.
6. Competitor Comparison : This part focuses on comparing competitor’s product in regards to fulfilling WHATs. This is also measured on scale of 1 to 5 where 1 denotes Highly Dissatisfied and 5 denotes Highly Satisfied.
7. Relative Importance –
   This part gives results by calculating total sum of each of HOWs by multiplying their Importance with value of Body Ranking symbol. This part is useful as it allows us to identify HOWs of products which require more attention and resources.
8. Lower Level or Foundation –
   This part of HOQ lists more specific target values for technical specifications in relation to HOWs in order to satisfy customer requirements.

Refer to the HOQ Diagram below :

The Roof Ranking System and Body Ranking System are as follows :

The formula for Computing Importance Weight and Relative Importance Weight :

Importance Weight, 
= Sum of (Importance Factor * Body Ranking Symbol Value) 

in column

Relative Importance Weight, 
= (Importance Weight/ Total Importance Weight) * 100 

For example, if column in HOWs is as follows :

Importance Weight (A) 
= (2 * 9 + 3 * 3 + 3 * 1) 
= 18 + 9 + 3 
= 30 

Similarly, Importance Weight of other technical requirements is calculated.