Specifying and Prototyping

Transcription

1 Contents Specifying and Prototyping M. EVREN KIYMAÇ What is Specifying? Gathering Specifications Specifying Approach & Waterfall Model What is Prototyping? Uses of Prototypes Prototyping Process Fidelity in Prototyping Prototyping Types Specifying vs. Prototyping Summary 2 3 At the beginning of every software project, the project manager is faced with a critical choice of approach. (1) The primary choices are: Building and Fixing: Proceed to build the full with minimal or no specifications. Rework the resulting product as necessary until it satisfies its users. Specifying: Develop a requirements specification for the product. Develop a design specification to implement the requirements. Develop the code to implement the design. Again, rework the resulting product as necessary. Prototyping: Build versions of parts of the product. Exercise the parts to determine how best to implement the operational product. Proceed to build the operational product, and again rework it as necessary. 4 Approach 1, Building and Fixing, has been shown to work poorly on most projects of any reasonable size. This is largely because of the highly increased cost of fixing a software product once it is completed and operational. The Specifying approach evolved to avoid the problems encountered in Building and Fixing and led to the familiar waterfall model of software development most frequently seen today. (1) 5 The Specifying approach has been highly successful in many application areas. However, it encounters difficulties in application areas in which it is hard to specify requirements in advance. This happens most frequently in human machine interface s, in which the requirements analyst often has to deal with user responses of the form, I m really not sure what I want, but I ll know it when I see it. (1) 6 In such situations stated in the previous slide, the Prototyping approach appears attractive. A number of papers have proposed refinements of the waterfall model of the software life cycle to incorporate prototyping t options. Some authors have gone so far as to suggest that prototyping options make all current life cycle models completely obsolete and even harmful.

2 What is Specifying? 7 Specifying is the process of determining the desired specifications of the product using methods such as: 1. Personal interviews, 2. Questionnaires, and 3. Research reports Software specification is the process of establishing what services are required and the constraints on the s operation and development. (3) Gathering Specifications 8 In order to gather software specifications, we do the requirements engineering process which consists of (2): Feasibility study elicitation and analysis specification validation Feasibility study Feasibility report Gathering Specifications elicitation and analysis System models 9 specification User and requirements Engineering Process validation document Specifying Approach & Waterfall Model 10 Specifying approach is the first step of waterfall model which consists of: analysis and definition System and software design Implementation and unit testing Integration and testing Operation and maintenance The drawback of the waterfall model is the difficulty of accommodating change after the process is underway. (8) Waterfall Model Problems of Waterfall Model definition System and software design Implementation and unit testing Integration and testing Operation and maintenance Difficult to establish all requirements explicitly, no room for uncertainty. Customer must have patience, not fast enough for delivery of modern internet based software. Major mistake can be disastrous. Unnecessary delays, blocking states. Inflexible partitioning of the project into distinct stages. This makes it difficult to respond to changing customer requirements Therefore, this model is only appropriate when the requirements are well understood. (2)

3 What is Prototyping? 13 A is an early sample or model built to test a concept or process or to act as a thing to be replicated or learned from. Prototype software is often referred to as alpha grade, meaning it is the first version to run. Often only a few functions are implemented, the primary focus of the alpha is to have a functional base code on to which features may be added. Once alpha grade software has most of the required features integrated into it, it becomes beta software for testing of the entire software and to adjust the program to respond correctly during situations unforeseen during development.(3) What is Prototyping? 14 Prototyping is the rapid development of a. In the past, the developed was normally thought of as inferior in some way to the required so further development was required. Now, the boundary between prototyping and normal development is blurred and many s are developed using an evolutionary approach. (2) Uses of Prototypes 15 The principal use is to help customers and developers understand the requirements for the ; elicitation: Users can experiment with a to see how the supports their work. validation: The can reveal errors and omissions in the requirements. Prototyping can be considered as a risk reduction activity which reduces requirements risks. (2) Benefits of Prototyping 16 Misunderstandings between software developers and users may be identified as the functions are demonstrated. Missing user services may be detected. Difficult to use or confusing user services may be identified and refined. Software development staff may find incomplete and/or inconsistent requirements as the is developed. A working is available early in the process. The may serve as a basis for deriving a specification. The can support user training and testing. (4) Prototyping Process 17 Prototyping Process 18 Build, evaluate, iterate, Establish objectives Define functionality Develop Evaluate Iterate rapidly at first, slow as design solidifies Increase fidelity and add detail. Change from paper to computer medium Prototyping plan Outline definition Executable Evaluation report Evaluate different aspects of the design at different stages of the design process. Early: metaphor, structure, usefulness Late: performance, learnability, satisfaction

4 Fidelity in Prototyping Fidelity refers to the level of detail. (5) Low fidelity artists renditions with many details missing High fidelity s look like the final product 19 Low Fidelity Prototyping 20 It is the rough cutting of the interface design created with paper, post it notes, overlays, correction tape, etc. Storyboards are sketched to show overall design concept and interface structure. Post its and overlays are used to simulate critical interactions. The is build to support the tasks. (6) Benefits of Low Fidelity Prototyping 21 Quick and cheap to build. Communicates design concept and structure, can demonstrate interactions. Facilitates t brainstorming i and invitesit discussion. i Enables early evaluation. Maximizes number of design refinements before you commit to code. Enables rapid and extensive exploration of the design space. Evaluating Low Fi Prototype 22 Big problems are identified. Rapid iteration is performed. Problems that empirical tests could miss (e.g., consistency issues) may be catched thd. Evaluations are only effective if the working team has the right skill set wants to improve the design, not defend it Evaluating Low Fi Prototype 23 High Fidelity Prototyping 24 This approach takes you as close as possible to a true representation of the product. Details are increased. More specifications are revealed. Images of the planned product is drawn with special computer applications. It is a lot more easier for customers to understand the product. (7)

5 Evolutionary prototyping: Prototyping Types 25 An approach to development where an initial is produced and refined through a number of stages to the final. Throw away prototyping: A which is usually a practical implementation of the is produced to help discover requirements problems and then discarded. The is then developed using some other development process. Evolutionary Prototyping 26 The is developed as a series of increments that are delivered to the customer. The objective of evolutionary prototyping is to deliver a working to end users. The development starts with those requirements which are best understood. Must be used for s where the specification cannot be developed in advance e.g. AI s and user interface s. Specification, design and implementation are inter twined Verification is impossible as there is no specification. Validation means demonstrating the adequacy of the.(4) Evolutionary Prototyping 27 Advantages of Evolutionary Prototyping 28 Accelerated delivery of the Develop abstract specification Build Use Rapid delivery and deployment are sometimes more important than functionality or long term software maintainability N User engagement with the Deliver YES System adequate? Not only is the more likely to meet user requirements, they are more likely to commit to the use of the Disadvantages of Evolutionary Prototyping Management problems 29 Existing management processes assume a waterfall model of development. Specialist skills are required which may not be available in all development teams. Maintenance problems Continual change tends to corrupt structure so long term maintenance is expensive. Contractual problems Throw away Prototyping 30 The objective of throw away prototyping is to validate or derive the requirements. The prototyping process starts with those requirements which are poorly understood.(4) Used to reduce requirements risk. The is developed from an initial specification, delivered for experiment then discarded. The throw away should NOT be considered as a final Some characteristics may have been left out. Thereis nospecification forlong term maintenance. The will be poorly structured and difficult to maintain.

6 Throw away Prototyping 31 Rapid Prototyping Techniques 32 Various techniques may be used for rapid development; Outline requirements Reusable components Develop Evaluate Specify Dynamic high level language development Database programming Componentand application i assembly Develop software Validate Delivered software These are not exclusive techniques they are often used together. Visual programming is an inherent part of most development s. Visual Programming 33 Scripting languages such as Visual Basic support visual programming where the is developed by creating a user interface from standard items and associating components with these items. A large library of components exists to support this type of development. These may be tailored to suit the specific application requirements. User Interface Prototyping 34 It is impossible to pre specify the look and feel of a user interfaceinaneffectiveway. Prototyping is essential. UI development consumes an increasing part of overall development costs. User interface generators may be used to draw the interface and simulate its functionality with components associated with interface entities. Web interfaces may be d using a web site editor. (2) Specifying vs. Prototyping 35 An experiment about the subject is made with seven software teams. They developed versions of the same small size ( source instruction) application software product. Four teams used the Specifying approach. Three teams used the Prototyping approach. (1) Specifying vs. Prototyping 36 The main results of the experiment were (1): Prototyping yielded products with roughly equivalent performance, but with about 40% less code and 45% less effort. The d products rated somewhat lower on functionality and robustness, but higher on ease of use and ease of learning. Specifying produced more coherent designs and software that was easier to integrate.

7 Specifying vs. Prototyping 37 Distribution of Project Effort by Activity Specifying vs. Prototyping 38 Performance Comparisons Summary 39 Both prototyping and specifying have valuable advantages that complement each other. For most large projects, and many small ones, a mix of prototyping and specifying will be preferable to the exclusive use of either by itself. A can be used to give end users a concrete impression of the s capabilities. Prototyping is becoming increasingly used for development where rapid development is essential. Summary 40 Throw away prototyping is used to understand the requirements. In evolutionary prototyping, the is developed by evolving an initial version to the final version. Prototyping is essential for parts of the such as the user interface which cannot be effectively prespecified. Users must be involved in evaluation. References Barry W. Boehm, Terence E. Gray, and Thomas Seewaldt, Prototypingvs. Specifying: a multi project experiment. 2. Ian Sommerville, Software Engineering, 6th Edition k k/l fe /h8 h 5. hccedl.cc.gatech.edu/getdocument.php?doc= _know_about_s_for_user_testing 8. Walt Scacchi, Process Models in Software Engineering. THANKS FOR YOUR PATIENCE 42