CS 425 625 Software Engineering Software Processes Based on

CS 425/625 Software Engineering Software Processes Based on Chapter 4 of the textbook [SE-8] Ian Sommerville, Software Engineering, 8 th Ed. , Addison-Wesley, 2006 and on Ch 4 PPT presentation from http: //www. software-engin. com/ September 21, 2009 1

Outline l l Software Process Models l Waterfall model l Evolutionary development l Component-based software engineering l Incremental model l Spiral model Software Process Activities l Specification l Design and implementation l Validation l Evolution The Rational Unified Process Computer-Aided Software Engineering 2

Software Process Models l l l Software process = organized set of activities aimed at building a software system Software process model = an abstract representation of a software process Fundamental software process activities: l l l Software specification Software design Software implementation Software validation Software evolution 3

Software Process Models: Waterfall. . l The Waterfall model [SE-8, Fig 4. 1] 4

Software Process Models: . Waterfall. l Main characteristics: l l l Also called classic software life cycle or sequential model Process activities (phases/stages) are clearly separated After a number of iterations, phases of the life cycle (such as specification and design) are “frozen” 5

Software Process Models: . . Waterfall l Advantages: l Organized approach, provides robust separation of phases l Reflects common engineering practice Disadvantages: l Doesn’t cope well with changes required by the client l Development teams might wait for each other l A working version of the product is available only late Applicability: l When requirements are well known and few changes are likely to be needed l Can be used also for parts of larger software systems 6

Software Process Models: Evolutionary Development… l Evolutionary Development model [SE-8, Fig 4. 2] 7

Software Process Models: . Evolutionary Development. . l Main characteristics: l The phases of the software construction are interleaved Feedback from the user is used throughout the entire process l The software product is refined through many versions l l Types of evolutionary development: l l Exploratory development Throw-away prototyping 8

Software Process Models: . . Evolutionary Development. l Advantages: l l Deals constantly with changes Provides quickly an initial version of the system Involves all development teams Disadvantages: l l l Quick fixes may be involved “Invisible” process, not well-supported by documentation The system’s structure can be corrupted by continuous change 9

Software Process Models: …Evolutionary Development l Disadvantages [cont’d]: l l l Special tools and techniques may be necessary The client may have the impression the first version is very close to the final product and thus be less patient Applicability: l l l When requirements are not well understood When the client and the developer agree on a “rapid prototype” that will be thrown away Good for small and medium-sized software systems 10

Software Process Models: Component-based Software Engineering… l CBSE process model [SE-8, Fig 4. 3] 11

Software Process Models: . Component-based Software Engineering. . l Main characteristics: l l Makes intensive use of existing reusable components The focus is on integrating the components rather than on creating them from the scratch 12

Software Process Models: . . Component-based Software Engineering. l Advantages: l l l Reduces considerably the software to be developed “inhouse” Allows faster delivery In principle, more reliable systems, due to using previously tested components 13

Software Process Models: …Component-based Software Engineering l Disadvantages: l l l Compromises in requirements are needed Less control over the system’s evolution Applicability: l l When there is a pool of existing components that could satisfy the requirements of the new product Emerging trend: integration of web services from a range of suppliers 14

Software Process Models: Incremental Development… l The Incremental model [SE-8, Fig 4. 4] 15

Software Process Models: . Incremental. . l Main characteristics: l l Hybrid model that combines elements of the waterfall and evolutionary paradigms The specification, design, and implementation phases are broken in smaller increments 16

Software Process Models: . . Incremental. l Advantages: l l l l Provides better support for process iteration Reduces rework in the software construction process Some decisions on requirements may be delayed Allows early delivery of parts of the system Supports easier integration of sub-systems Lower risk of project failure Delivery priorities can be more easily set 17

Software Process Models: . . . Incremental l Disadvantages: l l Increments need be relatively small Mapping requirements to increments may not be easy Common software features may be difficult to identify Applicability: l When it is possible to deliver the system “part-by-part” 18

Software Process Models: Spiral Model. . l Boehm’s Spiral Model [SE-8, Fig 4. 5] 19

. Software Process Models: Spiral Model. l Main characteristics: l l Also a hybrid model that support process iteration The process is represented as a spiral, each loop in the spiral representing a process phase Four sectors per loop: objective setting, risk assessment and reduction, development and validation, planning Risk is explicitly taken into consideration 20

Software Process Models: . . Spiral Model l Advantages: l l Disadvantages: l l Risk reduction mechanisms are in place Supports iteration and reflects real-world practices Systematic approach Requires expertise in risk evaluation and reduction Complex, relatively difficult to follow strictly Applicable only to large systems Applicability: l Internal development of large systems 21