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Software design A look from the field…

Software design A look from the field…. Ofer Egozi, CTO Babylon Ltd. Goals. Review some software design issues we came across at Babylon R&D Demonstrate the importance of some principles you study here, in the “real world”

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Software design A look from the field…

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  1. Software designA look from the field… Ofer Egozi, CTO Babylon Ltd.

  2. Goals • Review some software design issues we came across at Babylon R&D • Demonstrate the importance of some principles you study here, in the “real world” • But also show the constraints that cause us not to follow them, and what happens then

  3. Babylon – the company • Established in 1997, single-click dictionary • Internet global distribution, eyeballs model • Added conversions, user-created glossaries • Monetization attempts (2000) disappointing • Major restructure in 2001, team halved • Move to licensing model, retail + corporate • Added PRC, Enterprise information (2003) • Today growing, balanced, ~70 employees

  4. Babylon-Pro Basics OCR [ trap click , get context ] Content-Manager Local Glossaries Server Glossaries Server GUI Result-Manager Client

  5. 3.0 2.1 4.0 5.0 2.0 3.0 4.0 5.0 2.0 1.0 3.0 2.2 2.0 3.0 Babylon R&D – products Babylon-Pro Public Server Babylon-Builder Enterprise-Server 5.0 1997 1998 1999 2000 2001 2002 2003 2004 2005

  6. A lesson in what not to do… • High cohesion, low coupling, locality, understandability… • Versions 2.0 – 4.0 were almost anything but the above… example • Why? time to market, prototypes that become products, never time to rewrite • Still we survived until a rewrite could be prioritized (v5.0), toward the Enterprise-Server

  7. Inherent constraints • Millions of active users (can’t babysit at customer site, at least not retail…) • Backward compatibility major issue (BDC), hard to simulate in Technion assignments… • Retail market much less customer-driven, design may start earlier than full specs (U3) • At some stages, time to market critical, at others – not (and stability critical)

  8. Gloss BES Babylon-EnterpriseServer Public Server BES-ext Content Server Requestor XML/httpXML/”COM” Babylon Client Content Manager General architecture (5.0) Note: describes only BDC data sources!

  9. Content Server - Deja-vu • Don’t duplicate code – trivial, isn’t it? • Initially content serving was client code only (v2.0). Then, marketing demand for a quick online implementation (v2.1). • Main challenge – wrapper, core sources shared • With time, this on-demand porting was somewhat neglected, and coordination drifted • Only in 2004 (v5.0), code was restructured and unified, first as sources, then as a portable DLL

  10. Content Server – “classic” classes • What would you expect classes of a Glossaries’ Content Server be? • Surprisingly, we actually do use the real-life objects in these classes: CBDC, CBDCRecord,CBDCWordRecord, CBDCTranslationRecord, CBDCInfoRecord, CBDCTranslationsIndexTableReader • Observation 1: all these are internal, access is only through high level calls • Observation 2: additional, “physical” classes, e.g. BRandomAccessReader(low-level) or CBDCWordsTableReader (install/upgrade)

  11. Request/Persist - Abstraction • Recall architecture… • Request / Reply format (v4 example) • Configuration / Persistency (registry / .ini) • Natural unification solution: XML format • Proprietary – integrity-check, compress, typing • Markup interpreted to/from XML, interpreter is a portable recursive class • Designed to solve data integrity problem, then generalized and used throughout products

  12. JBanner - interpreter • J frequent prefix, but does not stand for Java…  • Element for proprietary advertising (2000), go beyond animated gif (no Flash then!) • Marketing requirements too unpredictable, wanted to allow maximum flexibility • Created a simple but powerful scripting language, power ranged from simple banners to arcade • Interpreter always adds a level of complexity, bridging it to “user-level” is important • In our case, it was not bridged… 

  13. BES-extensions - cake-baking • Recall architecture… • Enterprise-Server requestor implemented at first in public-server requestor • Very quickly, differences grew to be significant, and complicated code • Hard work invested to detach the BES-extensions module • Module then put in a DLL (BES client only) with a “narrow interface” to enforce

  14. Testing • We know how to do that, don’t we?  • I’d like to talk about: “Post-Testing” Testing?

  15. Post-Testing Testing - logs • QA is the process of finding bugs, not proving there aren’t any… • On release, load shifts from QA to support • Empower support using readable and detailed logging in Release (example) • More difficult to add good logs after development... • Development/debug logs should be cleaned and kept, with LogLevel support

  16. Post-Testing Testing - crashes • On the Complexity of Debugging Crashes…  • Until v3.1 (2000), many client crashes were X-files. Then, crash-reports were introduced. • Crash rate shrunk by an order of magnitude, crash visibility and investigate-ability rose  • Here’s what the user sees.... • Infrastructure – simple macros, embedded in main entry points and sensitive code • With time, recovery added too (use sparingly!!)

  17. The trivial rules of thumb  • Avoid “NIH” syndrome if possible… (example: GUI) • Trade-off between abstraction and speed (example: glossary installation) • Entire module rewrite gets a low priority a-priori – cause for developer frustration  • Rewrite is also dangerous - listen to Joel…

  18. That’s all folks… • Questions?… 

  19. Main header (partial)v3.1 , 2000

  20. Sample request/reply – v4.0 217.66.199.240 - - [04/Sep/2004:00:02:11 -0400] "GET /cgi-bin/trans40.cgi?00GFA2IAC3136FCJ0,645,385;748B;2AEF;1199;182A;87C;C01;11EE;638B;4EA;4E8;4F8;4E7;38E;4EB;38D;38C;38B;38A;4E4;389;9DA;388;4E5;387;386;390;38F;0:2:33:.AAcknowledgement HTTP/1.0" 200 6 "-" "Babylon"

  21. Babylon-Pro Basics – server_reg OCR [ trap click , get context ] Content-ManagerPersistency Request context Request Server GlossariesPersistency Local GlossariesPersistency Server GUIConfigurationLocalization Reply Reply Result-Manager DOM Client

  22. JBanner (interpreter)Email from marketing to R&D team leader…

  23. Logging – example (client init) • Support process flow

  24. Exception handling facilities • Code running at exception must be “thin”! • Example for CSHost service

  25. Shared client/server code (pre-v5.0)

  26. Shared C/S code (v5.0 - CSHost)

  27. When there is too much sugar… 

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