Requirements Engineering

Requirements Engineering

1. Type of Requirements

   • Functional: They describe what the system should do. Imprecision in this requirements may lead to changes and therefore delivery delays and cost increments.
   • Non-Functional: They specify or constrain characteristics of the system. This requirements are often more critical than individual functional requirements because failing to meet a non-functional requirement may lead to the whole system being unusable.
     • Product Requirements: These specify or constrain the runtime behavior of the software.
     • Organizational Requirements: These are requirements derived from policies and procedures in the customer's and developer's organizations.
     • External Requirements: They cover all requirements that are derived from factors external from the system and its development process.

2. Requirements Engineering Processes

   • Elicitation and Analysis: Discovering requirements by interacting with stakeholders.
   • Specification: Converting the requirements into a standard form.
   • Validation: Checking the requirements define the system that the customer wants.

3. Requirements Elicitation

   • 1. Requirements Discovery and Understanding: Interact with stakeholders of the system to discover their requirements.
   • 2. Requirements Classification and Organization: Organize the collection of requirements into coherent clusters.
   • 3. Requirements Prioritization and Negotiation: Requirements may conflict, so prioritizing requirements and finding and resolving requirements conflicts through negotiation is needed.
   • 4. Requirements Documentation: The requirements are maintained in documents, or informally on whiteboards, wikis, or other shared spaces.
   • Elicitation Techniques
     • Interviewing
     • Ethnography

4. Requirements Specification

   • Natural Language Specification: Has been used to write requirements since the 50's. It's expressive, intuitive and universal, but also potentially vague and ambiguous.
   • Structured Specifications: Way of writing system requirements where requirements are written in a standard way. It maintains most of the expressiveness and understandability of natural language but ensures to a degree uniformity on the specifications.
   • Use Cases: The are a way of describing interactions between users and a system using a graphical model and structured text.
   • Software Requirements Specification (SRS) Document: Official statement of what the developers should implement.
     • Structure
       • Glossary
       • User Requirements Definition
       • System Architecture
       • System Requirements Specification
       • System Models
       • System Evolution
       • Appendices
       • Introduction
       • Preface
       • Index

5. Requirements Validation

   • Validity Checks: These check that requirements reflect the real needs of the system users.
   • Consistency Checks: Check that requirements in the document don't conflict.
   • Completeness Checks: The document should include requirements that define all functions and constraints intended by the user.
   • Realism Checks: Ensure that the requirements can be implemented within the proposed budget and time.
   • Verifiability: Write a set of tests that can prove that the delivered system meets each specified requirement.