pyright Nancy Leveson, Sept 1999 Reuse (Assume have source code, not a commercial product) Ariane 5. Therac-25. British AtC Expectation Significantly lower development costs and time. Amortize costs among all users or uses Assumptions Will be reused enough to recoup extra costs Can easily and cheaply integrate components into a new environment(interoperability)
Copyright Nancy Leveson, Sept. 1999 Reuse (Assume have source code, not a commercial product) Ariane 5, Therac-25, British ATC, ... Expectation: Significantly lower development costs and time. Amortize costs among all users or uses. Assumptions: Will be reused enough to recoup extra costs Can easily and cheaply integrate components into a new environment (interoperability). � c
Reuse: Empirical data High reuse in some limited environments, not widespread however NASA Goddard study Garlan Allen Ockerbloom Performance problems(from large size and complexity) Complexity frequently inappropriate for tasks performed Trouble fitting components together In some cases, took significant reengineering to make the interoperate properly Maintaining synthesized system difficult in absence of low-level understanding
Copyright Nancy Leveson, Sept. 1999 Reuse: Empirical Data High reuse in some limited environments, not widespread c however. NASA Goddard Study Garlan, Allen, Ockerbloom: Performance problems (from large size and complexity) Complexity frequently inappropriate for tasks performed. Trouble fitting components together. In some cases, took significant reengineering to make the interoperate properly. Maintaining synthesized system difficult in absence of low-level understanding. �
Reuse: Empirical Data Siemens(hardware ASICs)reuse study Time to build a reusable component can be 120-150% of time needed to develop component for single use (excludes documentation) For reusuable component, needed to develop new documentation - took one to two times the effort of designing the component Overhead to develop a reusable component(design+ doc recaptured after fifth use Frequency of reuse increases with degree of comprehensibility Habitability even more important: measure of how"at home a potential user of reusable component feels. Highly subjective but effect even greater than that of comprehensibility
Copyright Nancy Leveson, Sept. 1999 Reuse: Empirical Data (2) Siemens (hardware ASICs) reuse study: Time to build a reusable component can be 120-150% of time needed to develop component for single use (excludes documentation). For reusuable component, needed to develop new documentation -- took one to two times the effort of designing the component. Overhead to develop a reusable component (design + doc) c recaptured after fifth use. Frequency of reuse increases with degree of comprehensibility. Habitability even more important: measure of how "at home" a potential user of reusable component feels. Highly subjective but effect even greater than that of comprehensibility. �
opyright Nancy Leveson, Sept. 1999 Reuse: Technical issues Configuration control problems May change continuously(any developer may be able to check out and change) Unneeded functionality(interoperability and performance issues) May need to write software utilities(restrictive wrappers) to restrict functionality Much of savings may be offset by need for more testing (Weyuker) Debugging may be significantly more difficult(Weyuker) Longevity --does potential for reuse decrease over time? Reuse designs rather than finished products?
c Copyright Nancy Leveson, Sept. 1999 Reuse: Technical Issues Configuration control problems May change continuously (any developer may be able to check out and change). Unneeded functionality (interoperability and performance issues) May need to write software utilities (restrictive wrappers) to restrict functionality. Much of savings may be offset by need for more testing (Weyuker) Debugging may be significantly more difficult (Weyuker) Longevity -- does ppotential for reuse decrease over time? Reuse designs rather than finished products? �
Reuse: Other Management issues(e. g, reward structures) Platforms and reuse at Xerox(hopefully, one of the Xerox students can tell us about this) One organization within Xerox reports they use half dozen different software platforms to build half dozen different products Achieve approximately 80-90%reuse other comments or experiences?
Copyright Nancy Leveson, Sept. 1999 c Reuse: Other Management issues (e.g., reward structures) Platforms and reuse at Xerox (hopefully, one of the Xerox students can tell us about this). One organization within Xerox reports they use half dozen different software platforms to build half dozen different products. Achieve approximately 80-90% reuse Other comments or experiences? �
Copyright Nancy Leveson, Sept. 1999 Main difference from reuse is lack of source code Potential advantages Reduce front-end acquisition or development costs Amortize costs over large number of users Compensate for lack of expertise shelley hayes Allow for more rapid infusion of technology But new risk drivers Loss of market control (less control leads to higher risks) High speed market Must deal with rapid obsolescence(shortened lifetimes) New versions or releases brought to market frequently For government, shift from buyers market"to"sellers market
c Copyright Nancy Leveson, Sept. 1999 COTS Main difference from reuse is lack of source code Potential advantages: Reduce front-end acquisition or development costs. Amortize costs over large number of users. Compensate for lack of expertise (Shelley Hayes) Allow for more rapid infusion of technology But new risk drivers Loss of market control (less control leads to higher risks) High speed market Must deal with rapid obsolescence (shortened lifetimes) New versions or releases brought to market frequently. For government, shift from "buyer’s market" to "seller’s market" �
opyright Nancy Leveson, Sept. 1999 COTS: Management lssues Lower development costs offset by higher lifetime costs? Sustainment"costs substantial -need to be planned and managed What if vendor goes out of business or stops producing and will not maintain old versions Even if escrow agreements hard to maintain software you did not write and must hire developers expert in that code Dependency on vendor. Can charge anything or make other demands(e.g, Microsoft case findings of fact Higher speed of change requires greater strategic flexibility Requires flexible and proaction system evolution management
c Copyright Nancy Leveson, Sept. 1999 COTS: Management Issues Lower development costs offset by higher lifetime costs? "Sustainment" costs substantial -- need to be planned and managed. What if vendor goes out of business or stops producing and will not maintain old versions? Even if escrow agreements, hard to maintain software you did not write and must hire developers expert in that code. Dependency on vendor. Can charge anything or make other demands (e.g., Microsoft case findings of fact). Higher speed of change requires greater strategic flexibility. Requires flexible and proaction system evolution management. �
COTS: Technical Issues Functionality provided may not remain what you need over time Few parts in a software system truly independent May need wrappers and patches as substitutes for real source-code-based maintenance Differences(e.g, timing) may be introduced in new products What happens when support from Cots vendor ceases? Can user change requests be satisfied? May be trojan horses or security flaws in COTS software and almost certainly will not know until too late
c Copyright Nancy Leveson, Sept. 1999 COTS: Technical Issues Functionality provided may not remain what you need over time. Few parts in a software system truly independent. May need wrappers and patches as substitutes for real source-code-based maintenance. Differences (e.g., timing) may be introduced in new products What happens when support from COTS vendor ceases? Can user change requests be satisfied? May be Trojan horses or security flaws in COTS software and almost certainly will not know until too late. �
COTS: Technical Issues Must be accepted"as is"and may not satisfy user requirements. Compromises may be required May be difficult or impossible to certify(safety) Need to defend yourself from mistakes in suppliers code Developed to commercial not government or safety standards Requires continuous lifetime system engineering effort Identify and integrate product obsolescence information with technology trends and new user requirements
c Copyright Nancy Leveson, Sept. 1999 COTS: Technical Issues (2) Must be accepted "as is" and may not satisfy user requirements. Compromises may be required. May be difficult or impossible to certify (safety). Need to defend yourself from mistakes in supplier’s code. Developed to commercial not government or safety standards. Requires continuous lifetime system engineering effort. Identify and integrate product obsolescence information with technology trends and new user requirements. �
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