4.17. REQUIREMENTS DEVELOPMENT

Purpose

The purpose of Requirements Development (RD) is to produce and analyze customer, product, and product component requirements.

Introductory Notes

This process area describes three types of requirements: customer requirements, product requirements, and product component requirements. Taken together, these requirements address the needs of relevant stakeholders, including those pertinent to various product lifecycle phases (e.g., acceptance testing criteria) and product attributes (e.g., safety, reliability, and maintainability). Requirements also address constraints caused by the selection of design solutions (e.g., integration of commercial off-the-shelf products).
All development projects have requirements. In the case of a project that is focused on maintenance activities, the changes to the product or product components are based on changes to the existing requirements, design, or implementation. The requirements changes, if any, might be documented in change requests from the customer or users, or they might take the form of new requirements received from the requirements development process. Regardless of their source or form, the maintenance activities that are driven by changes to requirements are managed accordingly.
Requirements are the basis for design. The development of requirements includes the following activities:
· Elicitation, analysis, validation, and communication of customer needs, expectations, and constraints to obtain customer requirements that constitute an understanding of what will satisfy stakeholders
· Collection and coordination of stakeholder needs
· Development of the lifecycle requirements of the product
· Establishment of the customer requirements
· Establishment of initial product and product component requirements consistent with customer requirements
This process area addresses all customer requirements rather than only product-level requirements because the customer may also provide specific design requirements.
Customer requirements are further refined into product and product component requirements. In addition to customer requirements, product and product component requirements are derived from the selected design solutions. Throughout the process areas, where we use the terms product and product component, their intended meanings also encompass services and their components.
Requirements are identified and refined throughout the phases of the product lifecycle. Design decisions, subsequent corrective actions, and feedback during each phase of the product’s lifecycle are analyzed for impact on derived and allocated requirements.
The Requirements Development process area includes three specific goals. The Develop Customer Requirements specific goal addresses defining a set of customer requirements to use in the development of product requirements. The Develop Product Requirements specific goal addresses defining a set of product or product component requirements to use in the design of products and product components. The Analyze and Validate Requirements specific goal addresses the necessary analysis of customer, product, and product component requirements to define, derive, and understand the requirements. The specific practices of the third specific goal are intended to assist the specific practices in the first two specific goals. The processes associated with the Requirements Development process area and those associated with the Technical Solution process area may interact recursively with one another.
Analyses are used to understand, define, and select the requirements at all levels from competing alternatives. These analyses include the following:
· Analysis of needs and requirements for each product lifecycle phase, including needs of relevant stakeholders, the operational environment, and factors that reflect overall customer and end-user expectations and satisfaction, such as safety, security, and affordability
· Development of an operational concept
· Definition of the required functionality
The definition of functionality, also referred to as “functional analysis,” is not the same as structured analysis in software development and does not presume a functionally oriented software design. In object-oriented software design, it relates to defining what are called “services” or “methods.” The definition of functions, their logical groupings, and their association with requirements is referred to as a “functional architecture.”
Analyses occur recursively at successively more detailed layers of a product’s architecture until sufficient detail is available to enable detailed design, acquisition, and testing of the product to proceed. As a result of the analysis of requirements and the operational concept (including functionality, support, maintenance, and disposal), the manufacturing or production concept produces more derived requirements, including consideration of the following:
· Constraints of various types
· Technological limitations
· Cost and cost drivers
· Time constraints and schedule drivers
· Risks
· Consideration of issues implied but not explicitly stated by the customer or end user
· Factors introduced by the developer’s unique business considerations, regulations, and laws
A hierarchy of logical entities (functions and subfunctions, object classes and subclasses) is established through iteration with the evolving operational concept. Requirements are refined, derived, and allocated to these logical entities. Requirements and logical entities are allocated to products, product components, people, or associated processes.
Involvement of relevant stakeholders in both requirements development and analysis gives them visibility into the evolution of requirements. This activity continually assures them that the requirements are being properly defined.
Related Process Areas
Refer to the Requirements Management process area for more information about managing customer and product requirements, obtaining agreement with the requirements provider, obtaining commitments with those implementing the requirements, and maintaining traceability.
Refer to the Technical Solution process area for more information about how the outputs of the requirements development processes are used, and the development of alternative solutions and designs used in refining and deriving requirements.
Refer to the Product Integration process area for more information about interface requirements and interface management.
Refer to the Verification process area for more information about verifying that the resulting product meets the requirements.
Refer to the Validation process area for more information about how the product built will be validated against the customer needs.
Refer to the Risk Management process area for more information about identifying and managing risks that are related to requirements.
Refer to the Configuration Management process area for information about ensuring that key work products are controlled and managed.

Specific Goal and Practice Summary

SG 1 Develop Customer Requirements
SP 1.1 Elicit Needs
SP 1.2 Develop the Customer Requirements
SG 2 Develop Product Requirements
SP 2.1 Establish Product and Product Component Requirements
SP 2.2 Allocate Product Component Requirements
SP 2.3 Identify Interface Requirements
SG 3 Analyze and Validate Requirements
SP 3.1 Establish Operational Concepts and Scenarios
SP 3.2 Establish a Definition of Required Functionality
SP 3.3 Analyze Requirements
SP 3.4 Analyze Requirements to Achieve Balance
SP 3.5 Validate Requirements

SP 1.1 Elicit Needs

Elicit stakeholder needs, expectations, constraints, and interfaces for all phases of the product lifecycle.
Eliciting goes beyond collecting requirements by proactively identifying additional requirements not explicitly provided by customers. Additional requirements should address the various product lifecycle activities and their impact on the product.
Examples of techniques to elicit needs include the following:
· Technology demonstrations
· Interface control working groups
· Technical control working groups
· Interim project reviews
· Questionnaires, interviews, and operational scenarios obtained from end users
· Operational walkthroughs and end-user task analysis
· Prototypes and models
· Brainstorming
· Quality Function Deployment
· Market surveys
· Beta testing
· Extraction from sources such as documents, standards, or specifications
· Observation of existing products, environments, and workflow patterns
· Use cases
· Business case analysis
· Reverse engineering (for legacy products)
· Customer satisfaction surveys

Examples of sources of requirements that might not be identified by the customer include the following:
· Business policies
· Standards
· Business environmental requirements (e.g., laboratories, testing and other facilities, and information technology infrastructure)
· Technology
· Legacy products or product components (reuse product components)

Subpractices
1. Engage relevant stakeholders using methods for eliciting needs, expectations, constraints, and external interfaces.

SP 1.2 Develop the Customer Requirements

Transform stakeholder needs, expectations, constraints, and interfaces into customer requirements.

The various inputs from the relevant stakeholders must be consolidated, missing information must be obtained, and conflicts must be resolved in documenting the recognized set of customer requirements. The customer requirements may include needs, expectations, and constraints with regard to verification and validation.
In some situations, the customer provides a set of requirements to the project, or the requirements exist as an output of a previous project's activities. In these situations, the customer requirements could conflict with the relevant stakeholders' needs, expectations, constraints, and interfaces and will need to be transformed into the recognized set of customer requirements after appropriate resolution of conflicts.
Relevant stakeholders representing all phases of the product's lifecycle should include business as well as technical functions. In this way, concepts for all product-related lifecycle processes are considered concurrently with the concepts for the products. Customer requirements result from informed decisions on the business as well as technical effects of their requirements.
Typical Work Products
1. Customer requirements
2. Customer constraints on the conduct of verification
3. Customer constraints on the conduct of validation
Subpractices
1. Translate the stakeholder needs, expectations, constraints, and interfaces into documented customer requirements.
2. Define constraints for verification and validation.
Keywords : appropriate ; customer ; customer requirement ; document ; process ; product ; product-related lifecycle processes ; project ; relevant stakeholder ; requirement ; stakeholder ; subpractice

SG 2 Develop Product Requirements

Customer requirements are refined and elaborated to develop product and product component requirements.

Customer requirements are analyzed in conjunction with the development of the operational concept to derive more detailed and precise sets of requirements called “product and product component requirements.” Product and product component requirements address the needs associated with each product lifecycle phase. Derived requirements arise from constraints, consideration of issues implied but not explicitly stated in the customer requirements baseline, and factors introduced by the selected architecture, the design, and the developer’s unique business considerations. The requirements are reexamined with each successive, lower level set of requirements and functional architecture, and the preferred product concept is refined.
The requirements are allocated to product functions and product components including objects, people, and processes. The traceability of requirements to functions, objects, tests, issues, or other entities is documented. The allocated requirements and functions are the basis for the synthesis of the technical solution. As internal components are developed, additional interfaces are defined and interface requirements are established.
Refer to the Maintain Bidirectional Traceability of Requirements specific practice of the Requirements Management process area for more information about maintaining bidirectional traceability.

SP 2.1 Establish Product and Product Component Requirements

Establish and maintain product and product component requirements, which are based on the customer requirements.

The customer requirements may be expressed in the customer’s terms and may be nontechnical descriptions. The product requirements are the expression of these requirements in technical terms that can be used for design decisions. An example of this translation is found in the first House of Quality Function Deployment, which maps customer desires into technical parameters. For instance, “solid sounding door” might be mapped to size, weight, fit, dampening, and resonant frequencies.
Product and product component requirements address the satisfaction of customer, business, and project objectives and associated attributes, such as effectiveness and affordability.
Derived requirements also address the cost and performance of other lifecycle phases (e.g., production, operations, and disposal) to the extent compatible with business objectives.
The modification of requirements due to approved requirement changes is covered by the “maintain” function of this specific practice; whereas, the administration of requirement changes is covered by the Requirements Management process area.
Refer to the Requirements Management process area for more information about managing changes to requirements.
Typical Work Products
1. Derived requirements
2. Product requirements
3. Product component requirements
Subpractices
1. Develop requirements in technical terms necessary for product and product component design.
Develop architecture requirements addressing critical product qualities and performance necessary for product architecture design.
2. Derive requirements that result from design decisions.
Refer to the Technical Solution process area for more information about developing the solutions that generate additional derived requirements.
Selection of a technology brings with it additional requirements. For instance, use of electronics requires additional technology-specific requirements such as electromagnetic interference limits.
3. Establish and maintain relationships between requirements for consideration during change management and requirements allocation.
Refer to the Requirements Management process area for more information about maintaining requirements traceability.
Relationships between requirements can aid in evaluating the impact of changes.

SP 2.2 Allocate Product Component Requirements

Allocate the requirements for each product component.

Refer to the Technical Solution process area for more information about allocation of requirements to products and product components. This specific practice provides information for defining the allocation of requirements but must interact with the specific practices in the Technical Solution process area to establish solutions to which the requirements are allocated.
The requirements for product components of the defined solution include allocation of product performance; design constraints; and fit, form, and function to meet requirements and facilitate production. In cases where a higher level requirement specifies performance that will be the responsibility of two or more product components, the performance must be partitioned for unique allocation to each product component as a derived requirement.
Typical Work Products
1. Requirement allocation sheets
2. Provisional requirement allocations
3. Design constraints
4. Derived requirements
5. Relationships among derived requirements
Subpractices
1. Allocate requirements to functions.
2. Allocate requirements to product components.
3. Allocate design constraints to product components.
4. Document relationships among allocated requirements.
Relationships include dependencies in which a change in one requirement may affect other requirements.

SP 2.3 Identify Interface Requirements

Identify interface requirements.

Interfaces between functions (or between objects) are identified. Functional interfaces may drive the development of alternative solutions described in the Technical Solution process area.
Refer to the Product Integration process area for more information about the management of interfaces and the integration of products and product components.
Interface requirements between products or product components identified in the product architecture are defined. They are controlled as part of product and product component integration and are an integral part of the architecture definition.
Typical Work Products
1. Interface requirements
Subpractices
1. Identify interfaces both external to the product and internal to the product (i.e., between functional partitions or objects).
As the design progresses, the product architecture will be altered by technical solution processes, creating new interfaces between product components and components external to the product.
Interfaces with product-related lifecycle processes should also be identified.
Examples of these interfaces include interfaces with test equipment, transportation systems, support systems, and manufacturing facilities.

2. Develop the requirements for the identified interfaces.
Refer to the Technical Solution process area for more information about generating new interfaces during the design process.
Requirements for interfaces are defined in terms such as origination, destination, stimulus, data characteristics for software, and electrical and mechanical characteristics for hardware.

SG 3 Analyze and Validate Requirements

The requirements are analyzed and validated, and a definition of required functionality is developed.

The specific practices of the Analyze and Validate Requirements specific goal support the development of the requirements in both the Develop Customer Requirements specific goal and the Develop Product Requirements specific goal. The specific practices associated with this specific goal cover analyzing and validating the requirements with respect to the user’s intended environment.
Analyses are performed to determine what impact the intended operational environment will have on the ability to satisfy the stakeholders’ needs, expectations, constraints, and interfaces. Considerations, such as feasibility, mission needs, cost constraints, potential market size, and acquisition strategy, must all be taken into account, depending on the product context. A definition of required functionality is also established. All specified usage modes for the product are considered, and a timeline analysis is generated for time-critical sequencing of functions.
The objectives of the analyses are to determine candidate requirements for product concepts that will satisfy stakeholder needs, expectations, and constraints; and then to translate these concepts into requirements. In parallel with this activity, the parameters that will be used to evaluate the effectiveness of the product are determined based on customer input and the preliminary product concept.
Requirements are validated to increase the probability that the resulting product will perform as intended in the use environment.

SP 3.1 Establish Operational Concepts and Scenarios

Establish and maintain operational concepts and associated scenarios.

A scenario is typically a sequence of events that might occur in the use of the product, which is used to make explicit some of the needs of the stakeholders. In contrast, an operational concept for a product usually depends on both the design solution and the scenario. For example, the operational concept for a satellite-based communications product is quite different from one based on landlines. Since the alternative solutions have not usually been defined when preparing the initial operational concepts, conceptual solutions are developed for use when analyzing the requirements. The operational concepts are refined as solution decisions are made and lower level detailed requirements are developed.
Just as a design decision for a product may become a requirement for product components, the operational concept may become the scenarios (requirements) for product components. Operational concepts and scenarios are evolved to facilitate the selection of product component solutions that, when implemented, will satisfy the intended use of the product. Operational concepts and scenarios document the interaction of the product components with the environment, users, and other product components, regardless of engineering discipline. They should be documented for all modes and states within operations, product deployment, delivery, support (including maintenance and sustainment), training, and disposal.
The scenarios may include operational sequences, provided those sequences are an expression of customer requirements rather than operational concepts.
Typical Work Products
1. Operational concept
2. Product or product component installation, operational, maintenance, and support concepts
3. Disposal concepts
4. Use cases
5. Timeline scenarios
6. New requirements
Subpractices
1. Develop operational concepts and scenarios that include functionality, performance, maintenance, support, and disposal as appropriate.
Identify and develop scenarios, consistent with the level of detail in the stakeholder needs, expectations, and constraints in which the proposed product or product component is expected to operate.
2. Define the environment in which the product or product component will operate, including boundaries and constraints.
3. Review operational concepts and scenarios to refine and discover requirements.
Operational concept and scenario development is an iterative process. The reviews should be held periodically to ensure that they agree with the requirements. The review may be in the form of a walkthrough.
4. Develop a detailed operational concept, as products and product components are selected, that defines the interaction of the product, the end user, and the environment, and that satisfies the operational, maintenance, support, and disposal needs.

SP 3.2 Establish a Definition of Required Functionality

Establish and maintain a definition of required functionality.

The definition of functionality, also referred to as “functional analysis,” is the description of what the product is intended to do. The definition of functionality can include actions, sequence, inputs, outputs, or other information that communicates the manner in which the product will be used.
Functional analysis is not the same as structured analysis in software development and does not presume a functionally oriented software design. In object-oriented software design, it relates to defining what are called “services” or “methods.” The definition of functions, their logical groupings, and their association with requirements is referred to as a functional architecture. (See the definition of “functional architecture” in the glossary.)
Typical Work Products
1. Functional architecture
2. Activity diagrams and use cases
3. Object-oriented analysis with services or methods identified
Subpractices
1. Analyze and quantify functionality required by end users.
2. Analyze requirements to identify logical or functional partitions (e.g., subfunctions).
3. Partition requirements into groups, based on established criteria (e.g., similar functionality, performance, or coupling), to facilitate and focus the requirements analysis.
4. Consider the sequencing of time-critical functions both initially and subsequently during product component development.
5. Allocate customer requirements to functional partitions, objects, people, or support elements to support the synthesis of solutions.
6. Allocate functional and performance requirements to functions and subfunctions.

SP 3.3 Analyze Requirements

Analyze requirements to ensure that they are necessary and sufficient.

In light of the operational concept and scenarios, the requirements for one level of the product hierarchy are analyzed to determine whether they are necessary and sufficient to meet the objectives of higher levels of the product hierarchy. The analyzed requirements then provide the basis for more detailed and precise requirements for lower levels of the product hierarchy.
As requirements are defined, their relationship to higher level requirements and the higher level defined functionality must be understood. One of the other actions is the determination of which key requirements will be used to track progress. For instance, the weight of a product or size of a software product may be monitored through development based on its risk.
Refer to the Verification process area for more information about verification methods that could be used to support this analysis.
Typical Work Products
1. Requirements defects reports
2. Proposed requirements changes to resolve defects
3. Key requirements
4. Technical performance measures
Subpractices
1. Analyze stakeholder needs, expectations, constraints, and external interfaces to remove conflicts and to organize into related subjects.
2. Analyze requirements to determine whether they satisfy the objectives of higher level requirements.
3. Analyze requirements to ensure that they are complete, feasible, realizable, and verifiable.
While design determines the feasibility of a particular solution, this subpractice addresses knowing which requirements affect feasibility.
4. Identify key requirements that have a strong influence on cost, schedule, functionality, risk, or performance.
5. Identify technical performance measures that will be tracked during the development effort.
Refer to the Measurement and Analysis process area for more information about the use of measurements.
6. Analyze operational concepts and scenarios to refine the customer needs, constraints, and interfaces and to discover new requirements.
This analysis may result in more detailed operational concepts and scenarios as well as supporting the derivation of new requirements.

SP 3.4 Analyze Requirements to Achieve Balance

Analyze requirements to balance stakeholder needs and constraints.

Stakeholder needs and constraints can address cost, schedule, performance, functionality, reusable components, maintainability, or risk.
Typical Work Products
1. Assessment of risks related to requirements
Subpractices
1. Use proven models, simulations, and prototyping to analyze the balance of stakeholder needs and constraints.
Results of the analyses can be used to reduce the cost of the product and the risk in developing the product.
2. Perform a risk assessment on the requirements and functional architecture.
Refer to the Risk Management process area for information about performing a risk assessment on customer and product requirements and the functional architecture.
3. Examine product lifecycle concepts for impacts of requirements on risks.

SP 3.5 Validate Requirements


Validate requirements to ensure the resulting product will perform as intended in the user's environment.

Requirements validation is performed early in the development effort with end users to gain confidence that the requirements are capable of guiding a development that results in successful final validation. This activity should be integrated with risk management activities. Mature organizations will typically perform requirements validation in a more sophisticated way using multiple techniques and will broaden the basis of the validation to include other stakeholder needs and expectations.
Examples of techniques used for requirements validation include the following:
· Analysis
· Simulations
· Prototyping
· Demonstrations

Typical Work Products
1. Record of analysis methods and results
Subpractices
1. Analyze the requirements to determine the risk that the resulting product will not perform appropriately in its intended-use environment.
2. Explore the adequacy and completeness of requirements by developing product representations (e.g., prototypes, simulations, models, scenarios, and storyboards) and by obtaining feedback about them from relevant stakeholders.
Refer to the Validation process area for information about preparing for and performing validation on products and product components.
3. Assess the design as it matures in the context of the requirements validation environment to identify validation issues and expose unstated needs and customer requirements.