1. © Copyright 1997, The University of New Mexico L-1 Computing Architecture Standards and Products

2. © Copyright 1997, The University of New Mexico L-2 Operating System: MVS Unix Netware MS Windows3.1, 3.11, 95

3. © Copyright 1997, The University of New Mexico L-3 Transaction Processing System IDMS/DC

4. © Copyright 1997, The University of New Mexico L-4 DBMS IDMS Oracle? NDBM MS Access Paradox

5. © Copyright 1997, The University of New Mexico L-5 Application Development Tools ADS SAS Visual Basic Cobol Developer 2000

6. © Copyright 1997, The University of New Mexico L-6 Ad Hoc Reporting Tools SAS Discoverer 2000? Culprit Visual Express?

7. © Copyright 1997, The University of New Mexico L-7 Query Language SQL

8. © Copyright 1997, The University of New Mexico L-8 Transport CAICCI SQL Net

9. © Copyright 1997, The University of New Mexico L-9 Security ACF2 NIS Netware

10. © Copyright 1997, The University of New Mexico L-10 Public Information Server FTP Gopher WWW

11. © Copyright 1997, The University of New Mexico L-11 Data Replication DB API ODBC OLE

12. © Copyright 1997, The University of New Mexico L-12 Network Printing LPR/LPD Netware

13. © Copyright 1997, The University of New Mexico L-13 Network Mgt. SNMP

14. © Copyright 1997, The University of New Mexico L-14 Network Protocol TCP/IP IPX

15. © Copyright 1997, The University of New Mexico L-15 Physical Network FDDI Enet

16. © Copyright 1997, The University of New Mexico L-16 Client / Server Applications

17. © Copyright 1997, The University of New Mexico L-17 Client – user side application Handles presentation

18. © Copyright 1997, The University of New Mexico L-18 Server – host side Stores persistent data Provides processing

19. © Copyright 1997, The University of New Mexico L-19 Procedural RPC remote procedure calls Named Pipes

20. © Copyright 1997, The University of New Mexico L-20 Object Oriented Classes, Inheritance, encapsulation, methods Smalltalk Java

21. © Copyright 1997, The University of New Mexico L-21 GUI Web Browser Windows Macintosh Motif

22. © Copyright 1997, The University of New Mexico L-22 Logic Server side Client-side

23. © Copyright 1997, The University of New Mexico L-23 Database Relational Network Transaction Processing Data Warehousing

24. © Copyright 1997, The University of New Mexico L-24 OSF DCE DFS – file service Time CDS – Naming DSF – Security (Kerberos)

25. © Copyright 1997, The University of New Mexico L-25 OSF DCE POSIX Threads DME – Management Transaction Processing

26. © Copyright 1997, The University of New Mexico L-26 SQL middleware

27. © Copyright 1997, The University of New Mexico L-27 Distributed Database Application uses data from multiple databases on different servers. 2 phase commit

28. © Copyright 1997, The University of New Mexico L-28 Thick Client Runs some or all of the application logic

29. © Copyright 1997, The University of New Mexico L-29 Thin client Does primarily or only display functions

30. © Copyright 1997, The University of New Mexico L-30 Partitioned Processing Both the server and the client have parts of the application processing

31. © Copyright 1997, The University of New Mexico L-31 CASE Tools Visual Development Tools –Paint objects from toolboxes –Event driven languages –SQL Database access

32. © Copyright 1997, The University of New Mexico L-32 End User Tools Personal DBs –Access, Paradox, FoxPRO, etc. Spreadsheets –Excel, Lotus, etc. DSS and EIS tools –Crystal. Gupta, Focus, Informix, Oracle, PowerSoft Analysis Tools –SAS, etc.

33. © Copyright 1997, The University of New Mexico L-33 CLIENT-SERVER COMPUTING

34. © Copyright 1997, The University of New Mexico L-34 CLIENT-SERVER COMPUTING A relatively new “buzz-word” for an old concept. To many vendors, any system that uses personal computers networked to a larger server is a “client- server” system. Even systems where the personal computer works solely in the terminal emulation are called client- server by some vendors. Such systems look exactly like the old mainframe-terminal systems except that the personal computer has replaced the terminal.

35. © Copyright 1997, The University of New Mexico L-35 CLIENT-SERVER COMPUTING (cont.) A true client-server application is one in which a complex application is decomposed into a part that runs on a server and one which runs on personal computers (the clients). Besides doing part of the computing for the application, the PC client provides a natural point and click graphical interface to the application.

36. © Copyright 1997, The University of New Mexico L-36 CLIENT-SERVER COMPUTING (cont.) Advances in networking and personal computers allows client-server applications to be more widely deployed today than has been possible in the past.

37. © Copyright 1997, The University of New Mexico L-37 SUBROUTINES AND CO-ROUTINES Y X Call Y Call X Application main subroutines Co-routines Uses subroutine callsUses co-routine calls Application

38. © Copyright 1997, The University of New Mexico L-38 CLIENT-SERVER APPLICATION Application Server Network Clients Server Appl. Client Appl. Remote Procedure Calls Responses usersusers Server Network Remote Clients Use Remote Procedure Calls (RPC’s) to communicate requests and pass responses.

39. © Copyright 1997, The University of New Mexico L-39 RPC’s Remote Procedure Calls are much more complex than subroutine or co-routine calls. Subroutine and co-routine calls are generally made within an application or between co-applications that run on a single system where the assumption can be made that data and command transfers will be error free.

40. © Copyright 1997, The University of New Mexico L-40 RPC’s (cont.) RPC’s, on the the other hand, are made between systems that are interconnected by means of an error- prone network. The server also must handle simultaneous requests from many clients. This also implies a need for synchronization among requests. All this makes RPC’s complex.

41. © Copyright 1997, The University of New Mexico L-41 ADVANTAGES OF CLIENT- SERVER Advantages often cited include: –Centralization - access, resources, and data security are controlled through the server –Scalability - any element can be upgraded when needed –Flexibility - new technology can be easily integrated into the system –Interoperability - all components (clients, network, servers) work together

42. © Copyright 1997, The University of New Mexico L-42 ADVANTAGES OF CLIENT- SERVER (cont.) Advantages often cited include: –Accessibility - server can be accessed remotely and across multiple platforms –Ease of application development –Lower total costs than “mainframe legacy systems”. –User friendly - familiar point and click interface

43. © Copyright 1997, The University of New Mexico L-43 DISADVANTAGES OF CLIENT- SERVER Disadvantages often cited include: –Dependability - when the server goes down, operations cease –Lack of mature tools - it is a relatively new technology and needed tools are lacking e.g.. Automated client software distribution –Lack of scalability - network operating systems (e.g.. Novell Netware, Windows NT Server) are not very scalable. –Higher than anticipated costs –Can cause network congestion

44. © Copyright 1997, The University of New Mexico L-44 DISADVANTAGES OF CLIENT- SERVER (cont.) NOTE –What some call advantages, others call disadvantages.

45. © Copyright 1997, The University of New Mexico L-45 THE REALITY OF CLIENT- SERVER Not a panacea - some successes, many early failures. More difficult to implement and more costly to maintain than originally thought. Technology relatively immature, but getting better Bottom line is you have to beware of vendor hype and analyze the suitability of client-server systems for a particular project on a case by case basis.

46. © Copyright 1997, The University of New Mexico L-46 CLIENT-SERVER ARCHITECTURES There are basically two types of client-server architectures –Two tier architectures –Three tier architectures The choice between the two should be made based on combination of: –Schedule for project implementation –Expected system changes and enhancements

47. © Copyright 1997, The University of New Mexico L-47 TWO-TIER ARCHITECTURES Application components are distributed between the server and client software In addition to part of the application software, the server also stores the data, and all data accesses are through the server. The presentation (to the user) is handled strictly by the client software. Server Network PC Clients

48. © Copyright 1997, The University of New Mexico L-48 TWO-TIER ARCHITECTURES (cont.) The PC clients assume the bulk of the responsibility for the application logic. The server assumes the bulk of the responsibility for data integrity checks, query capabilities, data extraction and most of the data intensive tasks, including sending the appropriate data to the appropriate clients.

49. © Copyright 1997, The University of New Mexico L-49 TWO-TIER ARCHITECTURES (cont.) SQL is a standard used on the clients to request appropriate subsets of data from the server. Data returned from the server to the clients is manipulated by the client software for reporting, business analysis, and “what if” analysis.

50. © Copyright 1997, The University of New Mexico L-50 TWO-TIER ARCHITECTURES, ADVANTAGES The commonly cited advantages of two-tier systems include: –Fast application development time –Available tools are robust and lend themselves to fast prototyping to insure user needs a met accurately and completely. –Conducive to environments with homogeneous clients, homogeneous applications, and static business rules.

51. © Copyright 1997, The University of New Mexico L-51 TWO-TIER ARCHITECTURES, DISADVANTAGES The commonly cited disadvantages of two-tier systems include: –Not suitable for dispersed, heterogeneous environments with rapidly changing business rules. –Because the bulk of the application logic is on the client, there is the problem of client software version control and new version redistribution. –Security can be complicated because a user may require separate passwords for each SQL server accessed.

52. © Copyright 1997, The University of New Mexico L-52 TWO-TIER ARCHITECTURES, DISADVANTAGES (cont.) The commonly cited disadvantages of two-tier systems include: –Client tools and SQL middleware in two-tier environments tend to be proprietary. The volatility of the client /server tool market raises questions about the long-term viability of any proprietary tool. Organizations should be wary about committing to proprietary tools.

53. © Copyright 1997, The University of New Mexico L-53 THREE-TIER ARCHITECTURES 3-tier architectures attempt to overcome some of the limitations of the 2-tier architecture by separating presentation, processing, and data into 3 separate and distinct entities. The software in the client handles the presentation (to the user) using similar tools as in the 2-tier architecture. Server Network PC Clients Server

54. © Copyright 1997, The University of New Mexico L-54 THREE-TIER ARCHITECTURES (cont.) When data or processing are required by the presentation client, a call is made to the middle-tier functionality server. This tier performs calculations, does reports, and makes any needed client calls to other servers (e.g.. a data base server).

55. © Copyright 1997, The University of New Mexico L-55 THREE-TIER ARCHITECTURES (cont.) Middle tier servers are usually coded in a highly portable, non-proprietary language such as C or C++. Middle tier servers may be multithreaded and can be accessed by multiple clients. The calling mechanism from client to server and from server to server is by means of RPC’s.

56. © Copyright 1997, The University of New Mexico L-56 THREE-TIER ARCHITECTURES (cont.) Because the bulk of 3-tier implementations use RPC’s and 2-tier implementations use SQL messaging, a careful examination of the merits of these respective request/response mechanisms is warranted.

57. © Copyright 1997, The University of New Mexico L-57 THREE-TIER ARCHITECTURES, ADVANTAGES Commonly cited advantages include: –RPC calls from the presentation client to the middle tier provide greater generality (i.e. flexibility) than the SQL calls usually used in the 2-tier architecture. –The 3-tier clients do not have to understand SQL. This allows the organization, names, or even the overall structure of back end data to changes without requiring changes in the PC-based presentation clients. This allows clients to access even non-relational databases and greatly simplifies introduction of new database technologies.

58. © Copyright 1997, The University of New Mexico L-58 THREE-TIER ARCHITECTURES, ADVANTAGES (cont.) Commonly cited advantages include: –Having separate functionality servers allows for the parallel development of individual tiers by application specialists. –Provides for more flexible resource allocation. Can reduce network traffic by having the functionality servers strip data to the precise structure needed before sending it to the clients.

59. © Copyright 1997, The University of New Mexico L-59 THREE-TIER ARCHITECTURES, ADVANTAGES (cont.) Commonly cited advantages include: –Can use reusable program modules for different applications, thus reducing development and migration costs. –3-tier standards such as OSF/DCE (Open Software Foundation Distributed Computing Environment) offers a variety of features to support distributed application development.

60. © Copyright 1997, The University of New Mexico L-60 THREE-TIER ARCHITECTURES, DISADVANTAGES Often cited disadvantages of 3-tier architectures include: –Creates an increased need for network traffic management, server load balancing, and fault tolerance. –Current tools are relatively immature and are more complex. –Maintenance tools are currently inadequate for maintaining server libraries. This is a potential obstacle for simplifying maintenance and promoting code reuse throughout the organization.

61. © Copyright 1997, The University of New Mexico L-61 CLIENT-SERVER BUZZWORDS Common client-server buzzwords include: –Thin clients –Fat clients –Message Server –Object Server –Fat Server –Middleware –3GL, 4GL

62. © Copyright 1997, The University of New Mexico L-62 CLIENT-SERVER BUZZWORDS (cont.) Since it is not unusual to get n different definitions of buzzwords from n different vendors, always ask what is meant by these “buzzwords”.