CS551 Advanced Software Engineering

1. CS551Advanced Software Engineering Yugi Lee STB #555 (816) 235-5932 leeyu@umkc.edu www.sice.umkc.edu/~leeyu CS551 - Lecture 2

2. Today’s Software Development • Development of large & complex systems • Software systems must fulfill the requirements of stakeholders (clients, end-users, developers,…) • Many people involved in the development • Software systems are expected to live long and be used by many people • Evolving technologies and computing environment CS551 - Lecture 2

3. The Software Crisis/Solution • 1968: NATO conference in Garmisch-Partenkirchen • Software crisis (to characterize the situation) • Increased quality demands on software products • High cost and time pressure • Shorter time to market • Coordination problems within the projects • Scarce resources • Software engineering (idea for a solution) CS551 - Lecture 2

4. What’s Software Crisis? • Unacceptably low quality of software • Delayed deadlines: Average 1 year • Over cost limits: Average 2X estimate • E.g. Air Force Command and Control system • Initial estimate • $1.5million • Winner’s bid • $0.4 million • Actual cost • $3.7 million • After deliver? • E.g. U.S Army study of • Federal projects • Delivered, but not used 47% • Paid for, but not delivered 29% • Abandoned or reworked 19% • Used after changes 3% • Used as delivered • 2% CS551 - Lecture 2

5. Example: Practical Disasters • European Space Agency Ariane 5 • Track control system failure results in self destruction • Denver Airport • Late delivery of software for the baggage system delays the opening of the airport by 16 months • US study (1995): 81 billion US$ spend per year for failing software development projects CS551 - Lecture 2

6. Why & What Software Engineering? • Why? ...to get away from ad hoc and unpredictable software development towards a systematic, understood one... • What? The application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software [IEEE-93] CS551 - Lecture 2

7. Three P’s • Education, skills, communication • Style ..... People Processes Products • Requirements, design, source code, executable, user documentation, test cases, test results, change request .... • Planning, coordination, management, measuring, • Analyzing, designing, coding, • ..... CS551 - Lecture 2

8. Why still Software Engineering? Has the software crisis vanished?No! • Software projects still run over time and out of budget • no break through in quality !!![still art instead of engineering discipline] Why is Software so Hard? • Software is [Parnas, 1985]: Buggy, Unreliable, Forever changing, Unwarrantable CS551 - Lecture 2

9. What is a Distributed System? • A collection of autonomous hosts that that are connected through a computer network. • Each host executes components and operates a distribution middleware • Middleware enables the components to coordinate their activities • Users perceive the system as a single, integrated computing facility. CS551 - Lecture 2

10. Hostn-1 Component1 Componentn Host2 Component1 Componentn Middleware Middleware Network Operating System Network Operating System Hardware Hardware Host1 Component1 Componentn Hostn Component1 Componentn Middleware Middleware Network Operating System Network Operating System Hardware Network Hardware What is a Distributed System? CS551 - Lecture 2

11. Component-Based Software Engineering? • An emerging concept called "a component-based software" appears to be a solution for the development of software system. • The component-based software engineering focuses on the entities (objects) developed and the components intended from their inception to be used within a framework in which they are placed in containers and combined with other components. CS551 - Lecture 2

12. Middleware Examples • Transaction-oriented • IBM CICS • BEA Tuxedo • IBM Encina • Microsoft Transaction Server • Message-oriented • Microsoft Message Queue • NCR TopEnd • Sun Tooltalk • Procedural • Sun ONC • Linux RPCs • OSF DCE • Object-oriented • OMG CORBA • Sun Java/RMI • Microsoft COM • Sun Enterprise Java Beans CS551 - Lecture 2

13. Centralized vs. Distributed System • One component with non-autonomous parts • Component shared by users all the time • All resources accessible • Software runs in a single process • Single Point of control • Single Point of failure • Multiple autonomous components • Components are not shared by all users • Resources may not be accessible • Software runs in concurrent processes on different processors • Multiple Points of control/failure CS551 - Lecture 2

14. Real World Example: Hong Kong Telecom … • Video-on-demand: provide subscribers with facilities to download videos from HK TK servers to low-cost Web-TVs. • currently 90,000 users. • Built using distributed object-technology. CS551 - Lecture 2

15. Requirements • Hardware: • Clients: Web-TV • Servers: RISC processor • Operating System Heterogeneity : • Clients: Java OS • Servers: UNIX • Programming Language Heterogeneity: • Clients: Java • Servers: C++ • Communication across Network • How to transmit complex data structures across the Internet? • Scale • Scaling from initially several hundred to currently 90,000 users • Security • Secure Payment • Authentication CS551 - Lecture 2

16. Why Distributed Object Technology? • Distributed: • Video clients need to download/show video on customer’s Web-TV • Multiple servers needs to be operated by Hongkong Telecom • Object Technology: • Video clients are written in Java: • Web-TV has Java Virtual Machine • portability to e.g. Sony Playstation, Sega-Console... • Video servers are written in C++: • high performance CS551 - Lecture 2

17. Another Example:IT Infrastructure of UBS Customer Information Services Authorisation Services Trading Workstation Product Database Services Marketing Services CS551 - Lecture 2 Host Services

18. Time to market Development of new applications with recent technology Integration of new applications increasingly difficult Scalability Management of 30,000,000 accounts Management of 10,000,000 customers Use by 2,000 concurrent users Reliability Hardware Heterogeneity Unisys Mainframes IBM Mainframes SPARC Servers PC Workstations Operating System Heterogeneity MVS UNIX Win-NT Programming Language Heterogeneity Cobol C/C++ Visual Basic Requirements CS551 - Lecture 2

19. Why Distributed Object Technology? • Uniform view of all banking services • Appropriate level of abstraction • Preserving investment by wrapping legacy applications • Exploiting advantages of object technology for new development • Resolving • distribution • heterogeneity CS551 - Lecture 2

20. Boeing 777 Configuration Mgmnt. CS551 - Lecture 2

21. Requirements • Scale • 3,000,000 parts per aircraft • Configuration of every aircraft is different • CAA regulations demand that records are kept for every single part of aircraft • Aircraft evolve during maintenance • Boeing produce 500 aircraft per year • Configuration database grows by 1.5 billion parts each year • Projected life of each aircraft 30 years • 45,000 engineers need on-line access to engineering data CS551 - Lecture 2

22. Requirements • COTS Integration • Existing IT infrastructure was no longer appropriate • Boeing could not afford to build required IT infrastructure from scratch • Components were purchased from several different specialized vendors • relational database technology • enterprise resource planning • computer aided project planning • Components needed to be integrated CS551 - Lecture 2

23. Requirements • Heterogeneity • 20 Sequent database machines as servers for the engineering data • 200 UNIX application servers • NT and UNIX workstations for engineers CS551 - Lecture 2

24. Why Distributed Object Technology • Object wrapping of COTS • Resolution of distribution at high level of abstraction • Resolution of heterogeneity • Scalability CS551 - Lecture 2

25. A Brief History of Objects Time DARM + OIL GRID WSDL RDF Peer-to-Peer UDDI 2000 XML DCOM Java UML SOAP COM 1990 CORBA OOAD HTML Eiffel DCE C++ 1980 Sun ONC Smalltalk Information Hiding 1970 Simula-67 CS551 - Lecture 2 Distributed Systems Software Engineering Languages

26. Distributed System Requirements • Integration of new, legacy and components off-the-shelf • Legacy components might not need to be re-engineered • COTS cannot be modified • Heterogeneity of • hardware platforms • operating systems • networks • programming languages • Construction of distributed systems CS551 - Lecture 2

27. Distributed System Requirements • What are we trying to achieve when we construct a distributed system? • Certain requirements are common to many distributed systems • Resource Sharing • Openness • Concurrency • Scalability • Fault Tolerance • Transparency CS551 - Lecture 2

28. Resource Sharing • Ability to use any hardware, software or data anywhere in the system. • Resource manager controls access, provides naming scheme and controls concurrency. • Resource sharing model (e.g. client/ server or object-based) describing how • resources are provided, • they are used and • provider and user interact with each other. CS551 - Lecture 2

29. Openness • Openness is concerned with extensions and improvements of distributed systems. • Detailed interfaces of components need to be published. • New components have to be integrated with existing components. • Differences in data representation of interface types on different processors (of different vendors) have to be resolved. CS551 - Lecture 2

30. Concurrency • Components in distributed systems are executed in concurrent processes. • Components access and update shared resources (e.g. variables, databases, device drivers). • Integrity of the system may be violated if concurrent updates are not coordinated. • Lost updates • Inconsistent analysis CS551 - Lecture 2

31. Scalability • Adoption of distributed systems to • accommodate more users • respond faster (this is the hard one) • Usually done by adding more and/or faster processors. • Components should not need to be changed when scale of a system increases. • Design components to be scalable! CS551 - Lecture 2

32. Fault Tolerance • Hardware, software and networks fail! • Distributed systems must maintain availability even at low levels of hardware/software/network reliability. • Fault tolerance is achieved by • recovery • redundancy CS551 - Lecture 2

33. Transparency • Distributed systems should be perceived by users and application programmers as a whole rather than as a collection of cooperating components. • Transparency has different dimensions that were identified by ANSA. • These represent various properties that distributed systems should have. CS551 - Lecture 2

34. Failure Transparency Scalability Transparency Performance Transparency Migration Transparency Replication Transparency Distribution Transparency Concurrency Transparency Access Transparency Location Transparency CS551 - Lecture 2

35. Access/Location Transparency • Access Transparency • Enables local and remote information objects to be accessed using identical operations. • E.g: File system operations in NFS, Navigation in the Web, SQL Queries • Location Transparency • Enables information objects to be accessed without knowledge of their location. • E.g: File system operations in NFS, Pages in the Web, Tables in distributed databases CS551 - Lecture 2

36. Concurrency/Replication Transparency • Concurrency Transparency • Enables several processes to operate concurrently using shared information objects without interference between them. • e.g, NFS, Automatic teller machine network, Database management system • Replication Transparency • Enables multiple instances of information objects to be used to increase reliability and performance without knowledge of the replicas by users or application programs • e.g, Distributed DBMS, Mirroring Web Pages. CS551 - Lecture 2

37. Failure/Migration Transparency • Failure Transparency • Enables the concealment of faults • Allows users and applications to complete their tasks despite the failure of other components. e.g. Database Management System • Migration Transparency • Allows the movement of information objects within a system without affecting the operations of users or application programs. e.g., NFS, Web Pages CS551 - Lecture 2

38. Scaling/Performance Transparency • Performance Transparency • Allows the system to be reconfigured to improve performance as loads vary. • E.g. Distributed make. • Scaling Transparency • Allows the system and applications to expand in scale without change to the system structure or the application algorithms. • E.g.,World-Wide-Web, Distributed Database CS551 - Lecture 2

39. Key Points • What is a Distributed Systems • Adoption of Distributed Systems is driven by Non-Functional Requirements • Distribution needs to be transparent to users and application designers • Transparency has several dimensions • Transparency dimensions depend on each other CS551 - Lecture 2