Cap4 Requirements engineering Flashcards
Cos’è il Requirements engineering?
The process of establishing the services that acustomer requires from a system and the constraints under which it operates and is developed.
The system requirements are the descriptions of the system services and constraints that are generated during the requirements engineering process
Differenza tra User requirements e System requirements?
User requirements
Dichiarazioni in un linguaggio naturale, più diagrammi (schemi) dei servizi
forniti e i loro limiti operativi. Scritto per i clienti.
System requirements
Un testo strutturato contenente una descrizione dettagliata delle funzioni di sistema, dei servizi e dei limiti operativi.
Definisce cosa dovrebbe essere implementato e quindi fare parte del contratto tra cliente e azienda
Cos’è un System stakeholders e che tipi di stakeholders esistono?
Any person or organization who is affected by the system in some way and so who has a legitimate interest
Stakeholder types:
End users
System managers
System owners
External stakeholders
Cosa sono i Functional requirements?
Describe functionality or system services.
Depend on the type of software, expected users and the type of system where the software is used.
Functional user requirements may be high-level statements of what the system should do.
Functional system requirements should describe the system services in detail.
Examples
A user shall be able to search the appointments lists for all clinics.
The system shall generate each day, for each clinic, a list of patients who are expected to attend appointments that day.
Each staff member using the system shall be uniquely identified by his or her 8-digit employee number.
Cosa sono i non-Functional requirements?
These define system properties and constraints e.g. reliability, response time and storage requirements. Constraints are I/O device capability, system representations, etc.
Process requirements may also be specified mandating a particular IDE, programming language or development method.
Non-functional requirements may be more critical than functional requirements. If these are not met, the system may be useless.
Quali sono le 3 macro categorie di non-Functional requirements?
Product requirements
Requirements which specify that the delivered product must behave in a particular way e.g. execution speed, reliability, etc.
Organisational requirements
Requirements which are a consequence of organisational policies and procedures e.g. process standards used, implementation requirements, etc.
External requirements
Requirements which arise from factors which are external to the system and its development process e.g. interoperability requirements, legislative requirements, etc.
Examples
Product requirement
The Mentcare system shall be available to all clinics during normal working hours (Mon–Fri, 0830–17.30). Downtime within normal working hours shall not exceed five seconds in any one day.
Organizational requirementUsers of the Mentcare system shall authenticate themselves using their health authority identity card.
External requirementThe system shall implement patient privacy provisions as set out in HStan-03-2006-priv.
Cosa sono i Requirements engineering processes?
The processes used for RE vary widely depending on the application domain, the people involved and the organisation developing the requirements.
However, there are a number of generic activities common to all processes
Requirements elicitation;
Requirements analysis;
Requirements validation;
Requirements management.
In practice, RE is an iterative activity in which these processes are interleaved.
Cos’è la Requirements elicitation?
Software engineers work with a range of system stakeholders to find out about the application domain, the services that the system should provide, the required system performance, hardware constraints, other systems, etc.
In quali fasi si divide la Requirements elicitation?
Requirements discovery
Interacting with stakeholders to discover their requirements. Domain requirements are also discovered at this stage.
Requirements classification and organisation
Groups related requirements and organises them into coherent clusters.
Prioritisation and negotiation
Prioritising requirements and resolving requirements conflicts.
Requirements specification
Requirements are documented and input into the next round of the spiral.
Cos’è la Requirements specification?
The process of writing donw the user and system requirements in a requirements document.
User requirements have to be understandable by end-users and customers who do not have a technical background.
System requirements are more detailed requirements and may include more technical information.
The requirements may be part of a contract for the system development
It is therefore important that these are as complete as possible.
Quali sono i modi in cui si può scrivere un system requirements specification ?
Natural language - The requirements are written using numbered sentences in natural language. Each sentence should express one requirement
Structured natural language - The requirements are written in natural language on a standard form or template. Each field provides information about an aspect of the requirement.
Design description languages - This approach uses a language like a programming language, but with more abstract features to specify the requirements by defining an operational model of the system. This approach is now rarely used although it can be useful for interface specifications.
Graphical notations - Graphical models, supplemented by text annotations, are used to define the functional requirements for the system; UML use case and sequence diagrams are commonly used.
Mathematical specifications - These notations are based on mathematical concepts such as finite-state machines or sets. Although these unambiguous specifications can reduce the ambiguity in a requirements document, most customers don’t understand a formal specification. They cannot check that it represents what they want and are reluctant to accept it as a system contract
Cosa sono gli Use cases?
Use-cases are a kind of scenario that are included in the UML.
Use cases identify the actors in an interaction and which describe the interaction itself.
A set of use cases should describe all possible interactions with the system.
High-level graphical model supplemented by more detailed tabular description (see Chapter 5).
UML sequence diagrams may be used to add detail to use-cases by showing the sequence of event processing in the system.
Qual è la struttura di un requirements document ?
Preface - this should define the expected readership of the document and describe its version history, including a rationale for the creation of a new version and a summary of the changes made in each version.
Introduction - This should describe the need for the system. It should briefly describe the system’s functions and explain how it will work with other systems. It should also describe how the system fits into the overall business or strategic objectives of the organization commissioning the software
Glossary - This should define the technical terms used in the document. You should not make assumptions about the experience or expertise of the reader.
User requirements definition - Here, you describe the services provided for the user. The nonfunctional system requirements should also be described in this section. This description may use natural language, diagrams, or other notations that are understandable to customers. Product and process standards that must be followed should be specified.
System architecture - This chapter should present a high-level overview of the anticipated system architecture, showing the distribution of functions across system modules. Architectural components that are reused should be highlighted.
System requirements specification - This should describe the functional and nonfunctional requirements in more detail. If necessary, further detail may also be added to the nonfunctional requirements. Interfaces to other systems may be defined.
System models - This might include graphical system models showing the relationships between the system components and the system and its environment. Examples of possible models are object models, data-flow models, or semantic data models.
System evolution - This should describe the fundamental assumptions on which the system is based, and any anticipated changes due to hardware evolution, changing user needs, and so on. This section is useful for system designers as it may help them avoid design decisions that would constrain likely future changes to the system.
Appendices - These should provide detailed, specific information that is related to the application being developed; for example, hardware and database descriptions. Hardware requirements define the minimal and optimal configurations for the system. Database requirements define the logical organization of the data used by the system and the relationships between data.
Index - Several indexes to the document may be included. As well as a normal alphabetic index, there may be an index of diagrams, an index of functions, and so on.
Cos’è il Requirements validation?
Concerned with demonstrating that the requirements define the system that the customer really wants.
Requirements error costs are high so validation is very important
Fixing a requirements error after delivery may cost up to 100 times the cost of fixing an implementation error.
Cosa controlla il Requirements checking?
Validity. Does the system provide the functions which best support the customer’s needs?
Consistency. Are there any requirements conflicts?
Completeness. Are all functions required by the customer included?
Realism. Can the requirements be implemented given available budget and technology
Verifiability. Can the requirements be checked?
