Information Systems Analysis and Design csc340 Information Systems Analysis and Design What Are Requirements VIII Requirements Analysis Requirements definition is a careful assessment of the needs that a system is to fulfill must say why a system is needed based on current and foreseen conditions which may be internal operations or an external market must say what system features will serve and satisfy this context must also say how the system is to be constructed Ross77 Requirements constitute a specification for the new system They serve as a contract between customers and developers Functional and Non Functional Requirements Stakeholders From Whom Do We Gather Requirements How Do We Specify Them 2004 John Mylopoulos Requirements Analysis 1 Information Systems Analysis and Design csc340 csc340 2004 John Mylopoulos Requirements Analysis 2 Information Systems Analysis and Design csc340 Functional Requirements Describe the processing i e functions to be supported by the new system Describe the inputs into the system Also describe the outputs of the system Finally they describe the data that must be managed by the system Requirements describe the system with respect to its environment NOT its inner workings 2004 John Mylopoulos Requirements Analysis 3 Information Systems Analysis and Design csc340 2004 John Mylopoulos Information Systems Analysis and Design Non Functional Requirements csc340 Are Requirements Always Done in Software Engineering Practice Describe how well the system supports the functional requirements hence the name nonfunctional or quality requirements This description may include Performance criteria Reliability requirements Security considerations Usability requirements more 2004 John Mylopoulos Requirements Analysis 4 Requirements Analysis 5 2004 John Mylopoulos Page Requirements Analysis 6 Information Systems Analysis and Design csc340 Information Systems Analysis and Design Whom Do We Gather Requirements From Stakeholders are Different for for Different Types of Projects From the stakeholders actors Users who are concerned about the features and the functionality of the new system Designers Systems analysts Training and user support staff Business analysts Technical authors The project manager more 2004 John Mylopoulos Customer driven projects develop customized one of solutions Market driven ones develop generic software that is sold in the market Coming soon User driven projects develop software that is downloaded and used for a fee on demand The concept of software is evolving from that of a custom built artifact to that of a commodity that you buy and soon to that of a service resource that you use on demand Requirements Analysis 7 Information Systems Analysis and Design csc340 csc340 2004 John Mylopoulos Requirements Analysis 8 Information Systems Analysis and Design What Do We Gather csc340 How Do We Specify Requirements Scenarios use cases from which we can infer functional and non functional requirements Scenarios describe desirable sequences of events that should be supported by the new system They also describe undesirable ones that should be prevented Through visual modeling The World The Model Designations Properties that only hold in the world Shared properties Properties that only hold in the model But Remember A Model is Usually just an Approximation 2004 John Mylopoulos Requirements Analysis 9 Information Systems Analysis and Design 2004 John Mylopoulos csc340 Additional Readings Readings Kotonya98 Kotonya G et all Requirements Engineering Processes and Techniques John Wiley Sons 1998 Macaulay96 Macaulay L Requirements Engineering Springer Verlag 1996 2004 John Mylopoulos Requirements Analysis 11 Page Requirements Analysis 10
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