2 Objectives Introduce the concepts User and System Requirements Describe functional and non-functional requirementsExplain how to document software requirements
3 Railway reservation system Who are the users of this system ?Financial Gateway(bank)ReservationSystemTravelerIVR systemTravel AgentSystem administratorReservation Clerk
4 Quiz 0Assume, you are analyzing an existing railway reservation system for devising enhancements. Answer the following questions with reference to any railway reservation system you are familiar with. Please write your assumptions clearly.i) Who are the various kinds of users of the system? What are their expectations of the system?ii) Will a system administrator who manages the system be a user? Justify your answer ?iii) List as many functional requirements of the system as possible ?iv) Write down five non-functional requirements of the system ?
5 Quiz 0 (contd.)v) Write down any additional requirements you would like to add to the system? (mention clearly whether they are functional or non-functional requirements)vi) Suppose, the system under study has no facility for making reservations using SMS. The customer wants this feature to be implemented. Is this requirement functional? If no, can you think of a way of implementing this non-functional requirement in terms of any existing functional requirements ?vii) What process model would you adopt in building the system? Explain why and give two other models you would not use, explaining why.
6 Users expectations : Traveler What are the Travelers expectations of the System ?Expects reservation, cancellation, adjustment, and enquiry facilities.Above facilities offered online and telephonic are highly appreciated
7 Users expectations : Travel Agent Travel Agents expectations of the SystemBulk reservation, cancellation, adjustment facilities.Enquiry facilities.Above facilities offered online and telephonic are highly appreciatedWants to be notified of important events like introduction of new / seasonal trains.
8 Users expectations : Reservation Clerk Reservation Clerks expectations of the SystemReservation, cancellation, adjustment, and enquiry facilities.Season ticket issuing facilityConcession handling facility like handling concessions given to senior citizens, Army personnel, students etc.Report generation facility. Ex: for generating daily sales reports etc.
9 Users expectations : System administrator System administrator’s expectations of the SystemA data backup facilityAn error recovery facilityAdding, removing new trains to the systemModifying train schedules and fares
10 Users expectations : Financial Gateway Financial gateway’s expectations of the SystemCommunication with the system should be safe to safeguard the integrity of the payment data.System should be using EDI or any other standard data interchange formats that the financial gateway understands.Note : Most of the external systems expectations are interoperability requirements.
11 Product requirements The reservation system product requirements High availability ( less MTBF )High throughput: handle more number of transactions per secondReliabilityScalabilitySecurity etc.
12 External requirements External requirements include:Interoperability requirements. Ex: Syntax and semantics of the messages to be used to communicate with the external systems.Legislative requirements. Ex: Personal information of a client should not be revealed to a third party without his consent.
13 Overall system requirements User RequirementsProduct RequirementsExternal Requirements
14 Requirements Engineering The process of establishing services that the customer requires from a system and the constraints under which it operates and is developed.The requirements are the descriptions of the system services and constraints that are generated during the requirements engineering process.Running example : Indian Railway Reservation System.
15 UsersThe stakeholders of the system, who interact with the system to accomplish their tasks.A user may be any entity that is interested in the services offered by the system.Eg : Traveler, Travel Agent, Reservation Clerk, Financial Gateway, System Administrator etc.
16 User RequirementsDifferent users have different expectations of the system behavior, and all these combined together constitute the overall system requirementsEx :-Traveler expects an easy to use online system for booking tickets.A reservation clerk expects a good user interface and response time for serving the customers efficiently.A payment gateway expects the communication with the system be very secure, to ensure the integrity of the payment data.
17 Types of RequirementsFunctional Requirements ( Application requirements )Eg: Cancellation, Reservation, enquiry etc.Non-Functional Requirements ( Quality Requirements )Eg:Reservation at counter should be closed by 8 p.m. every day.Online reservations should be allowed till 11 p.m. etc.,
18 Functional VS Non-functional requirements Describes an interaction between the system and its environmentFunctional requirements change less frequentlyNon-functional RequirementsDescribes a restriction or constraint that limit our choices for constructing a solutionMost of the changing requirements fall in to this categoryEx:- Some time later, Indian railway may decide to provide online reservation facility round the clock.
19 Classification of Non-functional requirements Product Requirements: defines product characteristicsEx: Execution speed, Reliability, Security, Scalability etc.Organizational Requirements: requirements which are a consequence of organizational policies and procedures.Ex: Operational time in railway reservation timeExternal Requirements: requirements which arise from factors external to the system.Ex: interoperability requirements, legislative requirements etc.
20 Characteristics of Requirements Are they correct ?Are they Consistent ?Are they Complete ?Are they Realistic ?Are they verifiable ?Are they traceable ?
21 Characteristics of Requirements . . Realistic Requirements : Are the requirements technically, financially, and operationally feasible ?Verifiable requirements : Should be able to verify whether a requirement is implemented correctly or notTraceable requirements : traceability is the ability to describe and follow the life of a requirement throughout the software development life cycle. This is a very useful feature used in change management.
22 Requirement Elicitation techniques Traditional TechniquesGroup elicitation techniquesPrototyping
23 Requirement Elicitation techniques Traditional TechniquesUse of questionnaires and surveysInterviewing stakeholdersAnalyzing existing systems and processes
24 Requirement Elicitation techniques Group elicitation techniquesA small group is formed, including some of the stakeholders also, to elicit requirements. This group brainstorms to define the requirements for the new system.This requirement gathering technique is very effective as the end users take active part in requirement definition.Group size should be reasonably small.Group composition: at least one representative from every group of end-users should be present in the group. This eliminates any bias in defining requirements.
25 Requirement Elicitation techniques PrototypingUsed when there is a great deal of uncertainty about the requirements, or where early feedback from stakeholders is needed.A prototype is:Built rapidly from initial requirementsAnalyzed to refine the requirementsNew prototype is developed from these new requirements.Process continues until requirements defined satisfactorily.
26 Why document requirements ? It will help clarify what you thinkIt is necessary to communicate with the usersIt is necessary to communicate with the development teamIt could form a basis for a contractual relationship
27 How to write it down ? Natural Language Structured Natural Language Graphical Notationsex. Use casesMathematical Specificationsex. finite state machines
28 Problems with natural language Lack of Clarity : precision is difficult without making the document difficult to read.Requirements Confusion: functional and non-functional requirements tend to be mixed-up.Requirements Amalgamation: several different requirements may be expressed together.Ambiguity: the readers and writers of the requirement must interpret the same words in the same way. Natural language is ambiguous so this is very difficult.Lack of Modularization: natural language structures are inadequate to structure system requirements.
29 Structured Natural Language A predefined template is used for documenting the requirements. All the requirements are written in a standard way.Each template defines a unique function (reqmt) or entity.Describes inputs and where they come from.Describes outputs and where they go to.Indicates other entities involved.Pre and Post conditions (if appropriate).The side effects (if any) of the function.
30 Structured Natural Language XYZ software/SRS/1.2.4Function:Description:Inputs:Source:Outputs:Destination:Action:Requires:Pre-condition:Post-condition:Side-effects:
31 Structured Natural Language contd… Indian railway reservation software/SRS/1.2.4Function: reservationDescription: makes a reservation on behalf of a customer, reservation clerk, or travel agent.Inputs: journey date, source station, destination station, train code etc.Source: customer / reservation clerk / travel agentOutputs: printed ticket or non-availability status messageDestination: customer / reservation clerk / travel agent
32 Structured Natural Language Indian railway reservation software/SRS/1.2.4Action: if seats/berths are available reserve them, otherwise send a non-availability status message to the userRequires:Pre-condition: required seats/berths are unreservedPost-condition: required seats/berths are reserved and no more available for reservation.Side-effects: None
33 Analysis ModelsUse cases, Sequence Diagrams, Class Diagrams, Object Diagrams, Collaboration Diagrams etc.to be discussed in the next class