1. 1 CS 501 Spring 2005 CS 501: Software Engineering Lecture 13 System Architecture and Design I

2. 2 CS 501 Spring 2005 Administration BOOM Wednesday, Duffield Atrium 4-6

3. 3 CS 501 Spring 2005 Quiz 2 Question 1 At the end of your CS 501 project, you mount your programs and documentation on GForge. The project team gives the client an unrestricted license to use the project for the client's purposes but not to distribute it to others. A year later, the members of your team decide to go into business, selling a product that is based on your CS 501 system. You start a small company and hire three programmers.

4. 4 CS 501 Spring 2005 Quiz 2 (a)You would like to keep the specification of the system secret. For this purpose you remove the system from GForge. Can you claim legal protection of the specification as trade secret? No. The presumption is that by placing it on the GForge for a year, trade secret protection was lost, unless the GForge site is securely protected and, from the very start, everybody who saw the specification was required to keep it secret.

5. 5 CS 501 Spring 2005 Quiz 2 (b) Your company extends the system with a new component. Can you protect the specification of the new component as trade secret? If so, what procedure would you follow? Yes, by creating procedures to keep the specification secret, e.g., by restricting access and my ensuring that everybody who has access understands the necessity of keeping it secret. (c) Who owns the copyright in the original system? Who owns the copyright in your new component? You own the copyright to the original system. To be more specific, the members of the project team jointly own the copyright. The company owns the copyright to the new component.

6. 6 CS 501 Spring 2005 Quiz 2 (d) Can you charge the CS 501 client money to use your new component? Yes. Unless your license says otherwise. (e)Two of your programmers leave and start their own company. What use can they make of the programs that they wrote while working for your company? Can they write new software based on the specification of your new component? They can make no use of the programs, without permission from the company. They were created as work for hire. They cannot write software based on this specification. The specification is a trade secret of the company. The former employees cannot use it, but they can use ideas from it.

7. 7 CS 501 Spring 2005 System Architecture and Design The overall design of a system: Computers and networks (e.g., monolithic, distributed) Interfaces and protocols (e.g., http, sql) Databases (e.g., relational, distributed) Security (e.g., smart card authentication) Operations (e.g., backup, archiving, audit trails) Software environments (e.g., languages, source control tools)

8. 8 CS 501 Spring 2005 UML: System and Subsystem Modeling Subsystem model A grouping of elements that specifies what a part of a system should do. Component (UML definition) "A distributable piece of implementation of a system, including software code (source, binary, or executable) but also including business documents, etc., in a human system." A component can be thought of as an implementation of a subsystem.

9. 9 CS 501 Spring 2005 UML Notation: Component & Node orderform.java A component is a physical and replaceable part of a system that conforms to and provides the realization of a set of interfaces. Server A node is a physical element that exists at run time and represents a computational resource.

10. 10 CS 501 Spring 2005 System Architecture Example: Extensibility in Web Browsers Web browsers provide a flexible user interface through an extensible architecture. Data types: helper applications, plug-ins Protocols: HTTP, WAIS, Gopher, FTP, etc. proxies Executable code: CGI scripts at server JavaScript at client Java applets Style sheets:

11. 11 CS 501 Spring 2005 Web Interface: Basic Web server Web browser Static pages from server All interaction requires communication with server

12. 12 CS 501 Spring 2005 UML Notation: Deployment Diagram WebBrowser PersonalComp WebServer DeptServer

13. 13 CS 501 Spring 2005 UML Notation: Application Programming Interface (API) API is an interface that is realized by one or more components. WebServer GetPost

14. 14 CS 501 Spring 2005 UML Notation: Interfaces WebBrowserWebServer HTTP dependency interface realization

15. 15 CS 501 Spring 2005 Web User Interface: CGI Script Web browser Scripts can configure pages Scripts can validate information All interaction requires communication with server Data CGI Scripts Web server

16. 16 CS 501 Spring 2005 UML Notation: CGI Interface Diagram CGIScript HTTP Apache CGI SQL MySQL These components might be located on a single node.

17. 17 CS 501 Spring 2005 Web User Interface: JavaScript Data CGI Scripts Web server Web browser JavaScripts can validate information as typed Some interactions are local Server interaction constrained by web protocols Java Script html

18. 18 CS 501 Spring 2005 UML Notation: Package A package is a general-purpose mechanism for organizing elements into groups. Note: Some authors draw packages with a different shaped box: JavaScript

19. 19 CS 501 Spring 2005 Example: Web Browser HTTP JavaScript HTMLRender Each package represents a group of objects. WebBrowser

20. 20 CS 501 Spring 2005 Web User Interface: Applet Any server Web servers Web browser Any executable code can run on client Client can connect to any server Applets

21. 21 CS 501 Spring 2005 Applet Interfaces WebBrowserWebServer HTTP XYZServer XYZInterface

22. 22 CS 501 Spring 2005 UML Diagrams and Specifications For every subsystem, there is a choice of diagrams Choose the diagrams that best model the system and are clearest to everybody. In UML every diagram must have supporting specification The diagrams shows the relationships among parts of the system, but much, much more detail is needed to specify a system explicitly. For example, in the Applet Interface slide, at the very least, the specification should include the version of the protocols to be supported at the interfaces, the options (if any), and implementation restrictions.

23. 23 CS 501 Spring 2005 Components and Classes Classes represent logical abstractions. They may be grouped into packages. Components represent physical things. They may live on nodes. Classes have attributes and operations directly. Components have operations that are reachable only through interfaces.

24. 24 CS 501 Spring 2005 Components and Replaceability Components allow system to be assembled from binary replaceable elements. A component is physical -- bits not concepts A component can be replaced by any other component(s) that conforms to the interfaces. A component is part of a system. A component provides the realization of a set of interfaces.

25. 25 CS 501 Spring 2005 System Design: Data Intensive Systems Examples Electricity utility customer billing Telephone company call recording and billing Car rental reservations (e.g., Hertz) Stock market brokerage (e.g., Charles Schwab) E-commerce (e.g., Amazon.com)

26. 26 CS 501 Spring 2005 Batch Processing Example: Electricity Utility Billing First attempt: Data input Master file Transaction Bill Each transaction is handled as it arrives.

27. 27 CS 501 Spring 2005 Transaction Types Create account / close account Meter reading Payment received Other credits / debits Check cleared / check bounced Account query Correction of error etc., etc., etc.,

28. 28 CS 501 Spring 2005 Criticisms of First Attempt Where is this first attempt weak? A bill is sent out for each transaction, even if there are several per day Bills are not sent out on a monthly cycle No way to answer customer queries No process for error checking and correction All activities are triggered by a transaction

29. 29 CS 501 Spring 2005 Batch Processing: Validation Data input Master file Edit & validation read only errors Batches of validated transactions Batches of incoming transactions

30. 30 CS 501 Spring 2005 UML Deployment Diagram: Batch Processing Validation MasterFile EditCheck ValidData DataInput RawData

31. 31 CS 501 Spring 2005 Batch Processing: Master File Update Master file update Bills Validated transactions in batches Sort by account errors Reports Instructions

32. 32 CS 501 Spring 2005 Interfaces to DataInput DataInput RawData EditCheckError UpdateError DataforCheck

33. 33 CS 501 Spring 2005 Benefits of Batch Updating All transactions for an account are processed together at appropriate intervals Backup and recovery have fixed checkpoints Better management control of operations Efficient use of staff and hardware

34. 34 CS 501 Spring 2005 Online Inquiry Master file read only Customer Service Customer Service department can read file, make annotations, and create transactions, but cannot change the master file. New transaction

35. 35 CS 501 Spring 2005 Online Inquiry: Use Cases CustomerServer AnswerCustomer NewTransaction >

36. 36 CS 501 Spring 2005 Data Intensive Systems Example: A Small-town Stockbroker Transactions Received by mail or over telephone For immediate or later action Complex customer inquiries Highly competitive market

37. 37 CS 501 Spring 2005 A Database Architecture Database(s): Customer and account database Financial products (e.g., account types, pension plans, savings schemes) Links to external databases (e.g., stock markets, mutual funds, insurance companies)

38. 38 CS 501 Spring 2005 Real-time Transactions Customer & account database Products & services database External services Real-time transactions

39. 39 CS 501 Spring 2005 Real-time Transactions & Batch Processing Customer & account database Products & services database External services Real-time transactions Batch processing Data input

40. 40 CS 501 Spring 2005 Stock Broker: Interface Diagram CustomerDB ProductDB OnLineTR BatchTR

41. 41 CS 501 Spring 2005 Architectural considerations to include in Specification Real-time service during scheduled hours with batch processing overnight Combine information from several databases Database consistency after any type of failure two-phase commit reload from checkpoint + log detailed audit trail How will transaction errors be avoided? How will transaction errors be corrected? How will staff dishonesty be controlled?

42. 42 CS 501 Spring 2005 Data Intensive Systems: Merger of Two Banks Each bank has a database with its customer accounts. The databases are used by staff at many branches and for back-office processing. The requirement is to integrate the two banks so that they appear to the customers to be a single organization and to provide integrated service from all branches. This is an example of working with legacy systems.

43. 43 CS 501 Spring 2005 Merger of Two Banks: Options ??? A B

44. 44 CS 501 Spring 2005 Merger of Two Banks: Architectural Options I.Convert everything to System A convert databases retrain staff enhance System A (software and hardware) discard System B II.Build an interface between the databases in System A and System B III.Extend client software so that it can interact with either System A or System B database