IS550: Software requirements engineering 1. Introduction and basic concepts Dr. Azeddine Chikh

IS550: Software requirements engineering 1. Introduction and basic concepts Dr. Azeddine Chikh

Text Soren Lauesen, "Software Requirements: Styles & Techniques" Addison-Wesley Professional 2002,  608 pp, ISBN-10: 0201745704 - ISBN-13: 9780201745702                  

1. The role of requirements Tacit demands & reqs Stakeholders Demands Elicitation Analysis Contract Reqspec Verification Validation Design Tracing: Forwards . . . Backwards . . . Req. management: Changing reqs Program Test Op & maint

1. The role of requirements Tacit demands : are necessary – we cannot specify everything Elicitation and analysis : finding and structuring requirements Validation: the customers check that requirements match demands Verification: checking that the product fulfills the requirements

1. The role of requirements Tracing : is needed to compare requirements against other information. There are 4 types of tracing Forward: Tracing from requirements to program Tracing from demands to requirements Backward: Tracing from program to requirements Tracing from requirements to demands

1. The role of requirements Req. management : in spite of attempts to get it right the first time requirements change during development. It must be easy to update the specification, add new requirements, and asses the consequences of change.

2. Project types There are many types of project: in-house development buying commercial software tenders and contracts, etc. Requirements have different roles in different types of projects Sometimes the project type is unknown

2. Project types Project types Customer Supplier In-house User dept. IT dept. Prod. devel. Marketing SW dept. Time & materials Company SW house COTS Company (Vendor) Tender Company Supplier Contract devel. Company SW house Sub-contracting Supplier SW house Unknown Inhouse? COTS?

2. Project types In-house development : Product development : The system is developed inside a company for the company’s own use. The customer and the supplier are departments of the same company Larger companies: banks, insurance comp., … Product development : The product is a commercial software to be marketed by a company The development project is carried out inside the company. The customer is the marketing department and the supplier the development department

2. Project types Time and materials based development: COTS purchase: A software house develops the system on a time-and-materials base, i-e the customer pays the costs, for instance month by month Requirements are informal (unwritten) and develop over time Over time, the parties tend to realize that such projects can easily get out of control. COTS purchase: Commercial Off The Shelf that we can buy from the market (more or less off the shelf) : MS-Office, development tools, hospital and bank systems We distinguish COTS purchase (fully off the shelf) from COTS based (including some tailor-made configuration or extension)

2. Project types Tender: Contract development: The costumer company starts a tender process and sends out a request for proposal (RFP). Several suppliers are invited to submit proposals The tender documentation contains an elaborate requirement specification The customer selects the best proposal Contract development: A supplier company develops or delivers a system to the customer company. The requirements specification and the contract specify what is to be delivered The two parties will often work together for some time to write the requirements and the contract. The system may be tailor-made or a COTS-based system with extensions

2. Project types Sub-contracting: Situation unknown: A subcontractor develops or delivers part of the system to a main contractor, who delivers the total system to a customer. Sub-contracting can be requirements-based or time-and-materials based without written requirements Situation unknown: In many cases the customer doesn’t know what should do. Should he buy a COTS system or have the system developed in-house ? Should he try to integrate several products or should he contract with someone else to do it? High-level requirements can help to resolve these issues. They may help compare the alternatives from a cost/benefit and risk perspective.

3. Contents of ReqSpec Quality reqs: Performance Usability Maintainability . . . Other deliverables: Documentation Install system Convert data Train users. . . Interfaces User groups Platform: HW, OS, DB Spreadsheet System Ext. products: Sensors, dev. Special SW Managerial reqs: Delivery time Legal Intellectual properties Development . . . Helping the reader: Background (Rationale) Business goals Definitions Diagrams . . . Organizing the parts: Best-known standard : IEEE 830 Data requirements: System state: Database, comm. states Input/output formats Functional requirements, each interface: Record, compute, transform, transmit Theory: F(input, state) -> (output, state) Function list, pseudo-code, activity diagram Screen prototype, support tasks xx to yy

4. Problems observed in practice Relatively few problems in data and functional requirements Serious problems ensuring efficient task support and meeting business goals Quality requirements : important, but what should be written ? Parts to help the reader : important, but often ignored

5. Domain and product level Product : the system to be delivered Product-level requirements : specify what should come in and out of the product. Domain : the product and its immediate users and other surroundings Domain-level requirements : describe the activities that go on outside the product – in the domain. The req. are to support those activities Quality req. can be at a product level as well as at a domain level. Example :performance 1: Product level : response time for the computer system (1) 2 : Domain level : performance time for a user task = manual time + (1) Clients : people served by the domain System : the product, the domain, or software plus hardware ?

5. Domain and product level Clients “Business” domain Actors? Platform Product User activities Control computers Domain I/O Product Elevators Product-level reqs: The product shall accept the following input: . . . Domain-level req: The product shall support the following user activities: . . .

5. Domain and product level Redefined limits “Business” domain Domain Product Control computers Clients User activities

6. The goal-design scale A requirement must specify what the system should do without specifying how. Goal-level requirement : why the customer wants to spend money on the product Domain-level requirement : supports user tasks xx to yy Product-level requirement : a function to be provided by the product Design-level requirement : details of the product interface

6. The goal-design scale R1. Our pre-calculations shall hit within 5% R2. Product shall support cost recording and quotation with experience data R3. Product shall have recording and retrieval functions for experience data R4. System shall have screen pictures as shown in app. xx Goal-level requirement Domain-level Product-level Design-level Which requirement to choose? If the supplier is A vendor of business applications? A software house - programmers? PriceWaterhouseCoopers?

6. The goal-design scale Ask “why” Neural diagnostics System shall have mini keyboard with start/stop button, . . . Why? Possible to operate it with “left hand”. Both hands must be at the patient. Electrodes, bandages, painful . . .

6. The goal-design scale Recommendations : Why+ How Measuring neural response is a bit painful to the patient. Electrodes must be kept in place . . . So both hands should be at the patient during a measurement. R1: It shall be possible to perform the commands start, stop, . . . with both hands at the patient. Might be done with mini keyboard (wrist keys), foot pedal, voice recognition, etc. Domain - why Req. Example - how In general it is an advantage to include “business” goals’, domain descriptions and - using more caution - examples.

7. Typical project models Product-level requirements : elicited from users. A lot of work Domain-level requirements : describe user tasks. Much faster. Two-step approach : domain-level first, design-level later with careful checks

7. Typical project models Approaches Traditional: Product-level reqs Ask users, study documents, . . . extract features/functions. Intro, [business goals] . . . System limits, e.g. context diagram Data reqs, e.g. data model, data descr. Product-level funct. reqs, e.g. features Critical quality reqs Two-step approach: Domain-level + design-level All the fast-approach stuff + Design-level reqs, e.g. prototypes, comm.protocols Fast approach: Domain-level Describe user tasks, study documents . . . Intro, [business goals, BPR tasks] . . . System limits, e.g. context diagram Data reqs, e.g. verbal data descr. Domain-level reqs, e.g. Tasks & Support [Trace analysis: goals to tasks] Critical quality reqs

7. Typical project models Recommended project models Project model Project type: Trad. Domain Two-step In-house ? OK OK Product dev. ? OK Time & mat. ? OK OK COTS business ? OK COTS tools OK Tender COTS ? OK Tender tailor ? OK  OK  Contract COTS ? OK Contract tailor ? OK  OK  Sub-contract OK OK Maintenance OK ? Used, but dubious  Variable price

8. Case studies A personal insulin pump An embedded system in an insulin pump used by diabetics to maintain blood glucose control. A mental health case patient management system A system used to maintain records of people receiving care for mental health problems. A wilderness weather station A data collection system that collects data about weather conditions in remote areas.

Insulin pump control system Collects data from a blood sugar sensor and calculates the amount of insulin required to be injected. Calculation based on the rate of change of blood sugar levels. Sends signals to a micro-pump to deliver the correct dose of insulin. Safety-critical system as low blood sugars can lead to brain malfunctioning, coma and death; high-blood sugar levels have long-term consequences such as eye and kidney damage.

Insulin pump hardware architecture

Activity model of the insulin pump

Essential high-level requirements The system shall be available to deliver insulin when required. The system shall perform reliably and deliver the correct amount of insulin to counteract the current level of blood sugar. The system must therefore be designed and implemented to ensure that the system always meets these requirements.

A patient information system for mental health care A patient information system to support mental health care is a medical information system that maintains information about patients suffering from mental health problems and the treatments that they have received. Most mental health patients do not require dedicated hospital treatment but need to attend specialist clinics regularly where they can meet a doctor who has detailed knowledge of their problems. To make it easier for patients to attend, these clinics are not just run in hospitals. They may also be held in local medical practices or community centres.

MHC-PMS The MHC-PMS (Mental Health Care-Patient Management System) is an information system that is intended for use in clinics. It makes use of a centralized database of patient information but has also been designed to run on a PC, so that it may be accessed and used from sites that do not have secure network connectivity. When the local systems have secure network access, they use patient information in the database but they can download and use local copies of patient records when they are disconnected.

MHC-PMS goals To generate management information that allows health service managers to assess performance against local and government targets. To provide medical staff with timely information to support the treatment of patients.

The organization of the MHC-PMS

MHC-PMS key features Individual care management Patient monitoring Clinicians can create records for patients, edit the information in the system, view patient history, etc. The system supports data summaries so that doctors can quickly learn about the key problems and treatments that have been prescribed. Patient monitoring The system monitors the records of patients that are involved in treatment and issues warnings if possible problems are detected. Administrative reporting The system generates monthly management reports showing the number of patients treated at each clinic, the number of patients who have entered and left the care system, number of patients sectioned, the drugs prescribed and their costs, etc.

MHC-PMS concerns Privacy Safety It is essential that patient information is confidential and is never disclosed to anyone apart from authorised medical staff and the patient themselves. Safety Some mental illnesses cause patients to become suicidal or a danger to other people. Wherever possible, the system should warn medical staff about potentially suicidal or dangerous patients. The system must be available when needed otherwise safety may be compromised and it may be impossible to prescribe the correct medication to patients.

Wilderness weather station The government of a country with large areas of wilderness decides to deploy several hundred weather stations in remote areas. Weather stations collect data from a set of instruments that measure temperature and pressure, sunshine, rainfall, wind speed and wind direction. The weather station includes a number of instruments that measure weather parameters such as the wind speed and direction, the ground and air temperatures, the barometric pressure and the rainfall over a 24-hour period. Each of these instruments is controlled by a software system that takes parameter readings periodically and manages the data collected from the instruments.

The weather station’s environment

Weather information system The weather station system This is responsible for collecting weather data, carrying out some initial data processing and transmitting it to the data management system. The data management and archiving system This system collects the data from all of the wilderness weather stations, carries out data processing and analysis and archives the data. The station maintenance system This system can communicate by satellite with all wilderness weather stations to monitor the health of these systems and provide reports of problems.

Additional software functionality Monitor the instruments, power and communication hardware and report faults to the management system. Manage the system power, ensuring that batteries are charged whenever the environmental conditions permit but also that generators are shut down in potentially damaging weather conditions, such as high wind. Support dynamic reconfiguration where parts of the software are replaced with new versions and where backup instruments are switched into the system in the event of system failure.

Key points Software engineers have responsibilities to the engineering profession and society. They should not simply be concerned with technical issues. Professional societies publish codes of conduct which set out the standards of behaviour expected of their members. Three case studies are used in the book: An embedded insulin pump control system A system for mental health care patient management A wilderness weather station