【文章內(nèi)容簡(jiǎn)介】 ndresult than a smaller stack of paper? 169。 2021, Univ ersity of C alifornia, Irv ine Lecture 11 Manageable Complexity vs… 169。 2021, Univ ersity of C alifornia, Irv ine Lecture 11 …Unmanageable Complexity ? Software cannot be easily abstracted ? Formulas ? Only in very few domains ? Diagrams, graphs, and other representations ? Typically nonhierarchical ? Far too many crossreferences ? Few concepts are available to use in an abstraction ? Tension between highlevel understanding and lowlevel detailed specification ? Highlevel understanding leaves out important details ? Aggregation often does not work 169。 2021, Univ ersity of C alifornia, Irv ine Lecture 11 Environment Can Be Changed vs… 169。 2021, Univ ersity of C alifornia, Irv ine Lecture 11 …Environment Cannot Be Changed ? Software has to adhere to the “world” in which it is placed ? Cannot change the hardware ? Cannot change the way people do business ? The “world” is often not clearly specified ? How can you change something that you cannot specify? ? Leads to many software changes ? Perception is that software is easier to change 169。 2021, Univ ersity of C alifornia, Irv ine Lecture 11 No Major Changes vs… 169。 2021, Univ ersity of C alifornia, Irv ine Lecture 11 …Major Changes ? Software is remarkably easy to change ? Change the source code, repile, rerun ? “One line here, one line there” ? Unfortunately, even small changes can have disastrous consequences ? A single wrong character can surreptitiously change the behavior of the software ? The effects of most changes are only visible in certain circumstances ? Sometimes, the environment does change ? Software is used in different anizations ? Software is used for different purposes 169。 2021, Univ ersity of C alifornia, Irv ine Lecture 11 Drastic Consequences ? Deceased patients ? Xray machine delivered very high doses because of a timing problem in its control software ? Crashed planes ? Software prevented pilots from performing emergency maneuvers ? Software had similar codes for different airports ? Decreased national security ? NSA puters down for four days due to a “software problem” Peter Neumann’s Risks Digest: 169。 2021, Univ ersity of C alifornia, Irv ine Lecture 11 A n a l y s i s2%S p e c i f i c a t i o n5%D e s i g n6%M o d u l e C o d i n g5%M o d u l e T e s t i n g7%I n t e g r a t i o n8%M a i n t e n a n c e67%High Cost [Schach] 169。 2021, Univ ersity of C alifornia, Irv ine Lecture 11 Cost of Change Progressively Higher 020406080100120140160180200A n a l y s i s S p e c i f i c a t i o n D e s i g n I m p l e m e n t a t i o n I n t e g r a t i o n M a i n t e n a n c e[Schach] 169。 2021, Univ ersity of C alifornia, Irv ine Lecture 11 Processes as a Remedy ? Institute processes through which software is engineered ? Cover all steps from initial idea and requirements to delivery, maintenance, and final retirement ? Make sure we do the right things/things right ? Make sure we do not fet to do anything ? Different processes for different kinds of software ? Not a silver bullet [Brooks “No Silver Bullet”] ? Software is still intrinsically difficult to deal with ? Processes help, but cannot guarantee anything Remember: People + Processes + Tools ? Product 169。 2021, Univ ersity of C alifornia, Irv ine Lecture 11 Processes ? Elements ? Activities (“Phases”) ? Artifacts ? Can include process specifications ? Resources ? People (their time and their cost) ? Tools (their time and their cost) ? Relationships between the elements ? Precedence, requires, provides, refines to, … ? Constraints ? Time ? Cost ? Qualities (repeatable process?) 169。 2021, Univ ersity of C alifornia, Irv ine Lecture 11 Software Life Cycle Models ? Buildandfix ? Waterfall ? Rapid prototyping ? Incremental ? Synchronizeandstabilize ? Spiral A software life cycle model is a highlevel process 169。 2021, Univ ersity of C alifornia, Irv ine Lecture 11 BuildandFix Build first version Modify until client is satisfied Operations mode Retirement Development Maintenance 169。 2021, Univ ersity of C alifornia, Irv ine Lecture 11 BuildandFix Build first version Modify until client is satisfied Operations mode Retirement Development Maintenance 169。 2021, Univ ersity of C alifornia, Irv ine Lecture 11 BuildandFix Build first version Modify until client is satisfied Operations mode Retirement Development Maintenance 169。 2021, Univ ersity of C alifornia, Irv ine Lecture 11 BuildandFix Build first version Modify until client is satisfied Operations mode Retirement Development Maintenance 169。 2021, Univ ersity of C alifornia, Irv ine Lecture 11 BuildandFix Build first version Modify until client is satisfied Operations mode Retirement Development Maintenance 169。 2021, Univ ersity of C alifornia, Irv ine Lecture 11 BuildandFix Build first version Modify until client is satisfied Operations mode Retirement Development Maintenance 169。 2021, Univ ersity of C alifornia, Irv ine Lecture 11 BuildandFix Build first version Modify until client is satisfied Operations mode Retirement Development Maintenance 169。 2021, Univ ersity of C alifornia, Irv ine Lecture 11 BuildandFix Build first version Modify until client is satisfied Operations mode Retirement Development Maintenance 169。 2021, Univ ersity of C alifornia, Irv ine Lecture 11 BuildandFix Build first version Modify until client is satisfied Operations mode Retirement Development Maintenance 169。 2021, Univ ersity of C alifornia, Irv ine Lecture 11 Waterfall Operations mode Retirement Requirements phase