Software Models Henning Schulzrinne Apr 2, 2023 Advanced Programming

Software Models Henning Schulzrinne Apr 2, 2023 Advanced Programming Spring 2002

Introduction Non-technical interlude. Many more type of software than before: commercial projects contract shareware open source Influences: commercial needs IP protection & licensing documentation support Apr 2, 2023 Advanced Programming Spring 2002 2

Commercial Classical model, but many variations Internal vs. for sale e.g., Columbia SSOL vs. PeopleSoft One time vs. retail only run one (or few copies) custom programming missile control retail aka “shrink wrap”, but also download or “ship and enable” games: cartridges embedded – OS, peripheral, cell phones, industrial control, . Apr 2, 2023 Advanced Programming Spring 2002 3

Commercial software Many different licenses: single computer (Microsoft XP) multiple computers by same owner (e.g., laptop and home) – common for consumer software IP address (servers) floating license – “no more than 3 simultaneous users” (CAD and SE tools) single network (e.g., within Columbia) – site license Apr 2, 2023 Advanced Programming Spring 2002 4

Contract Consulting – individually or through consulting houses, e.g., ArthurAndersen, EDS or Wipro (India) “Work for hire” – output belongs to customer (GRA vs. undergraduate!) Usually, specific to customer Often, outside of core competency of client (e.g., gov’t, hospital, .) Billed by project or by hour Apr 2, 2023 Advanced Programming Spring 2002 5

Shareware not open source can freely download binaries usually low-cost, limited functionality items (e.g., create buttons for web pages) “crippleware”: limited functionality (can’t save work) or time limit on usage mostly Mac and Windows Apr 2, 2023 Advanced Programming Spring 2002 6

Open source www.opensource.org Free redistribution Source code distribute either unobfuscated source code or binaries Derived works same license as original code Integrity of author’s source code allow distribution of modified code Apr 2, 2023 Advanced Programming Spring 2002 7

Open Source No discrimination against persons or groups No discrimination against fields of endeavor commercial use, non-military use Not specific to product not just if part of some distribution Must not restrict other software can’t require other software to be opensource Apr 2, 2023 Advanced Programming Spring 2002 8

Open Source Examples of open-source licenses: GNU General Public License modifications are also GPL GNU Library (Lesser) Public License allow linking into non-GPL code BSD license least restrictive – allow commercial use Artistic license force new naming for modifications Apr 2, 2023 Advanced Programming Spring 2002 9

Almost open-source Lots of programs that are free and/or provide source code, but: don’t allow modification (TeX) non-commercial or educational use only limited to particular hardware may be patent-encumbered (e.g., audio codecs) only for customer (e.g., in case supplier goes bankrupt) Apr 2, 2023 Advanced Programming Spring 2002 10

Example: BSD license Copyright (c) YEAR , OWNER All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. Neither the name of the ORGANIZATION nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, Apr 2, 2023 . Advanced Programming Spring 2002 11

Open source arguments “The Cathedral and the Bazaar” (Eric Raymond) Social arguments knowledge dissemination avoid wasted effort (“doing it anyway”) cf. pro bono by lawyers skill strengthening and visibility (academics) Technical arguments quality security standards-compliance testing on many systems Apr 2, 2023 Advanced Programming Spring 2002 12

Cathedral and the Bazaar 1. Every good work of software starts by scratching a developer's personal itch. 2. Good programmers know what to write. Great ones know what to rewrite (and reuse). 3. Plan to throw one away; you will, anyhow.'' (Fred Brooks, The Mythical Man-Month'', Chapter 11) 4. If you have the right attitude, interesting problems will find you. Apr 2, 2023 Advanced Programming Spring 2002 13

Cathedral and the Bazaar 5. When you lose interest in a program, your last duty to it is to hand it off to a competent successor. 6. Treating your users as co-developers is your least-hassle route to rapid code improvement and effective debugging. 7. Release early. Release often. And listen to your customers. 8. Given a large enough beta-tester and co-developer base, almost every problem will be characterized quickly and the fix obvious to someone. 9. Smart data structures and dumb code works a lot better than the other way around. 10. If you treat your beta-testers as if they're your most valuable resource, they will respond by becoming your most valuable resource. Apr 2, 2023 Advanced Programming Spring 2002 14

Cathedral and the Bazaar 11. 12. 13. 14. 15. 16. 17. The next best thing to having good ideas is recognizing good ideas from your users. Sometimes the latter is better. Often, the most striking and innovative solutions come from realizing that your concept of the problem was wrong. Perfection (in design) is achieved not when there is nothing more to add, but rather when there is nothing more to take away.'' Any tool should be useful in the expected way, but a truly great tool lends itself to uses you never expected. When writing gateway software of any kind, take pains to disturb the data stream as little as possible. When your language is nowhere near Turing-complete, syntactic sugar can be your friend. A security system is only as secure as its secret. Beware of pseudo-secrets. Apr 2, 2023 Advanced Programming Spring 2002 15

Open source successes TeX (not quite open-source) gcc compiler and tools Linux and *BSD (FreeBSD, OpenBSD, NetBSD) operating systems Apache web server sendmail mail transport agent (MTA) gimp bitmap graphics tool Tcl, Perl, Python language implementations Apr 2, 2023 Advanced Programming Spring 2002 16

Open source - problems Ideal: small group of authors write code, thousands contribute bug fixes (not just bug reports!) and enhancements Need large community of technical users less likely to work well for recipe management or kid’s games more forgiving of lack of documentation or clean install can integrate different tools if not, author becomes tech support Apr 2, 2023 Advanced Programming Spring 2002 17

Open source - problems Thus, works less well for specialized programs with small user base (hundreds) – get mostly complaints Mostly individuals moon-lighting or paid by unrelated company (e.g., Linus Torvalds) Business model uncertain: packaging (Red Hat) tech support contract (MySQL) free with hardware (IBM) grants and donations Apr 2, 2023 Advanced Programming Spring 2002 18

Which model is “right”? Commercial needs: size of customer base who pays? Intellectual property issues are there patents? does employer rely on IPR (trade or sell)? Documentation how much documentation is needed to make the program useful? How much support is needed? open-source support: mean vs. variance Apr 2, 2023 Advanced Programming Spring 2002 19

“Levels” of programming Programmable applications add macro to Excel Code generators generate UI code from “wizard” Application embedding new UI for IE or Mozilla Web scripting no UI in normal sense “Classical” application Java, C use mostly OS and UI APIs Apr 2, 2023 Advanced Programming Spring 2002 20

“Levels” of programming Device drivers and OS kernel embedded systems specialty OS (e.g., VxWorks) or no OS\ often, lower-end processors no virtual memory no cache limited memory space special operations (e.g., DSP MAC) Specialty programming: language compilers Apr 2, 2023 Advanced Programming Spring 2002 21