Purpose 

Non-Functional requirements analysis examines the requirements for the solution that define how well the functional requirements must perform. It specifies criteria that can be used to judge he operation of the system rather than specific behaviors.

Business Analysis Body of Knowledge^® (BABOK^®)

Non-functional requirements are often called us the quality attributes of the system. The plan for implementing the non-functional requirements is detailed in the system architecture, because they are usually significant requirements. Functional requirements define what a system is suppose to do and non-functional requirements define how a system is supposed to be. The other terms for the non-functional requirements are called as qualities, quality goals, quality of service requirements, constraints, and technical requirements. They judge the analysis based on responsiveness, security, usability, portability, and other non-functional standards that are critical to the success of the project. It will also allow you to impose the constraints and restrictions on the design of the system across the various agile systems.

Non-functional requirements are often associated with system solutions, and they also apply more broadly to both the processes and people aspects of the solutions. They augment the functional requirements of the solution, identify the constraints on those requirements, and describe the quality attributes a solution must exhibit based on the functional requirements. Non-functional requirements are typically expressed in textual formats as declarative statements. The declarative non-functional requirements has the constraining factors with them to analyze the problem. Non-functional requirements ensure the usability and effectiveness of the entire project. It will satisfy the internal business needs, users, and the market needs which will fulfill the mandatory non-functional requirements.

Some of the articles related to Non-functional Requirements analysis techniques are as follows,

• Non-functional Requirements - https://personal.utdallas.edu/~chung/SYSM6309/NFR-18-4-on-1.pdf
• Non-functional Requirements Analysis - https://sparxsystems.com/enterprise_architect_user_guide/14.0/guidebooks/tech_non_functional_requirements_analysis.html
• Specification of Non-functional Requirements - https://www.altexsoft.com/blog/business/functional-and-non-functional-requirements-specification-and-types/
• Examples of Non-functional Requirements - https://theappsolutions.com/blog/development/functional-vs-non-functional-requirements/
• Deliverable of Non-functional Requirements Analysis - https://www.oversee-project.com/fileadmin/oversee/deliverables/D1.5_Non_Functional_requirements_analysis_v1.6.pdf
• Non-functional Requirements Design - https://link.springer.com/book/10.1007/978-3-319-18344-2
• Defining Non-functional Requirements - http://bredemeyer.com/pdf_files/NonFunctReq.PDF
• Techniques of Non-functional Requirements - https://www.visual-paradigm.com/guide/requirements-gathering/requirement-analysis-techniques/
• Software for Non-functional Requirements Analysis - https://www.wisdomjobs.com/e-university/software-requirement-analysis-and-specifications-interview-questions.html
• Risk Driven Non-functional Requirements Analysis - https://pdfs.semanticscholar.org/ac8f/638b68e9d5e82dfd553efd723dd6716e1317.pdf

Non-functional requirements specifies how a system should perform a function, including the constraints and minimum requirements. Non-functional requirements are the quality attributes of the system which includes performance, reliability, recover-ability, security, data integrity and usability. The template for the non-functional requirement are categorized based on the performance and the areas in which the non-functional requirements are to be applied. The main elements of the non-functional requirements analysis are,

• Categories of non-functional requirements - It includes,
• Availability - A degree to which the solution is operable and accessible when required for use.
• Compatibility - A degree to which the solution operates effectively with other components in its environment.
• Functionality - A degree to which the solutions functions meet the users needs, including the aspects of accuracy and suitability.
• Maintainability - With which a solution can be modified to correct the fault and improve the performance.
• Performance Efficiency - A degree to which a solution performs its designated functions with minimum consumption of resources.
• Portability - With which a solution can be transferred from one environment to another.
• Reliability - Ability of the solution to perform its required functions under stated conditions for a specified period of time.
• Security - That protect the solution content or the solution components from malicious access or the destruction.
• Usability - With which a user can learn to use the solution.
• Certification - Constraints on the solution that are necessary to meet the certain standards.
• Localization - Requirements dealing with local languages, cultures, laws, and other characteristics of the users, which require attention to the context.
• Service Level Agreements - Constraints of the organization being served by the solution that are formally agreed by both the provider and the user of the solution.
• Extensible - The ability of the solution to incorporate new functionality.
• Measurement of non-functional requirements - Non-functional requirements often describe the quality of the characteristics in terms, such as the process must be easy to learn or the system must respond quickly. To be useful to develop a solution and to be verifiable, non-functional requirements must be quantified whenever possible. The measurement of non-functional requirements is guided by the source of the requirement.
• Context of non-functional requirements - The context is considered depending on the category of the non-functional requirements. Determining the optimal solutions for the non-functional requirements in a given organizational context is important for delivering the value to the stakeholders. Business analysts consider the relative stability of the context when evaluating the non-functional requirements.

Some of the books for Non-functional Requirements analysis techniques,

• Non-functional Requirements : Techniques for Defining | Thomas Hathaway | https://www.amazon.com/Functional-Non-Functional-Requirements-Decomposition-Fundamentals-ebook/dp/B01LIUJQF0/ref=sr_1_1?dchild=1&keywords=non-functional+requirements+analysis+books&qid=1592381468&sr=8-1
• Non-functional Requirements : Risk, Reliability, and Quality | Kevin Mac Adams | https://www.amazon.com/Non-functional-Requirements-Systems-Analysis-Reliability/dp/3319386646/ref=sr_1_2?dchild=1&keywords=non-functional+requirements+analysis+books&qid=1592381603&sr=8-2
• Mastering Non-functional Requirements Analysis | Sameer Paradkar | https://www.amazon.com/Mastering-Non-Functional-Requirements-architecture-assessment-ebook/dp/B07171M38T/ref=sr_1_3?dchild=1&keywords=non-functional+requirements+analysis+books&qid=1592381603&sr=8-3