1. Chapter 5 Middleware

2. Page 2 Middleware Software: in context of smart environment Software to provide services to facilitate –Rapid development –Ease of integration –Improved reliability –Increased scalability Lies between applications software & platform Connectivity software that joins applications thru communication mechanisms creating transparency, scalability, & interoperability

3. Page 3 Middleware Defined by API it provides to applications that use it & by protocols it supports Should reduce complexities –Of networks, OS, applications Should provide cross-platform infrastructure Should improve the system

4. Page 4 Overview of Middleware 1. Understanding of Middleware 2. Desirable characteristics 3. Different forms –Advantages/disadvantages 4. Technologies 5. Standards 6. Benefits * Provide a working knowledge base *

5. Page 5 Perceive-Reason-Act AI Approach Use to define characteristics of Middleware Perceive: sensors –Software to read, store, calibrate, etc. Reason: AI applications –Software to reason about the environment & provide actions Act: controllers –To change environment See Figure 5.1, pg. 104 What are the communications requirements?

6. Page 6 Needs of System (Figure 5.1) Interoperability: 2+ entities communicate Reliability: guarantee delivery Efficiency: minimize consumption & delivery time Throughput: lots of data, no bottlenecks Distributed network: applications not on single computer

7. Page 7 Wants of System Provide for future extensions & contingencies Scalable Hot - swappable - don't shut down to change component or application Secure Highly available - running, accessible Fault - tolerant

8. Page 8 Desirable Characteristics of System Simplicity and power: for developers & for API Natural & seamless extension of development environment: for implementer - so focus stays on application Flexibility for easy modifications of software - separation of interface from applications Maintainability Reusability Portability

9. Page 9 Middleware Architecture Communication is the focus Client - server model (Figure 5.3, pg. 107) –3-tier for much Middleware –Middle tier addition Increase in number of clients Better flexibility, maintainability, reusability, scalability

10. Page 10 Forms of Middleware Middleware sits between OS & application Huge number of products Vary in "form" –Role, terminology, composition Overview of key forms –Transaction -- Object –RPC -- Agent –Message -- Database –Web

11. Page 11 Transaction Processing Middle tier of processing routines between system that provides transaction-based services & clients –e.g.: ATM - deposit, withdraw, check balance –See Figure 5.4, pg. 109 Advantages –Independence of layers, database –Easily customized on all components –Transparency –Mature & well-tested efficient, reliable

12. Page 12 Transaction Processing Disadvantages –Limited scalability - each client (ATM) adds overhead –Older - uses low-level languages Examples: IBM's CISTP, BEA TUXEDO

13. Page 13 Message-Oriented (MOM) Provides communication between applications on one or more machines; different platforms (Figure 5.5, pg. 109) Generally asynchronous Message queuing, persistence (delays), delivery Peer-to-peer connectivity; agreed upon protocols

14. Page 14 Message-Oriented (MOM) Advantages –Simplifies cross-platform issues; portability –Increased operability, flexibility –Good for event-driven systems –Mature (1980's) Disadvantages –Asynchronous allows for network overload –Not implemented for some platforms Example: Oracle, Advanced Queuing, Arjuna Messaging, IBM MQ Series, MS MSMQ

15. Page 15 Object-Oriented aka Object-Oriented Brokers (ORB) Transparent extensions of object-oriented development environment, –Figure 5.6, pg. 110 Support: interface definition language, O communication mechanisms, O activation/location mechanisms Facilitate: locating objects & establishing communication - similar to MOM

16. Page 16 Object-Oriented aka Object-Oriented Brokers (ORB) Advantages - Same as MOM –Familiarity with object-oriented environment –Provide for rapid integration –Preserves separation between implementation & interface Disadvantages –Different ORB's support different levels of service, platforms, certain object-oriented languages –May be difficult to find one that supports all needs Examples: OMG's CORBA, MS COM/DCOM, Sun's JAVA RMI

17. Page 17 Database Can be complex Need API access to standard database interfaces Development connectivity tools & language extensions to facilitate applications to database Advantages –Standardization, simple Disadvantages –Not always cross platform –May not support advanced database features –May provide blocking, synchronous connections

18. Page 18 Remote Procedure Call (RPC) Stubs embedded in client-server applications at compile, facilitate calls between client-server (Figure 5.7, pg. 111) Advantages –Provide consistency of procedure calls locally & remotely –Network transparency of client-server location Disadvantages –Most are synchronous - forces call-wait scenario, possible blockages –Asynchronous mechanisms add complexity to development –Synchronous - not good for object-oriented or peer-to-peer Example: Open Group's Dist. Computing Environment

19. Page 19 Web Services Popular - bridge interface gap between application hidden by network security (e.g. firewalls) Leverages WWW technologies & protocols (Figure 5.8, pg. 112) –XML interface –HTTP communications New technologies –SOAP - Simple Object Access Protocol –WSDL - Web Services Definition Language

20. Page 20 Web Services Advantages –Ubiquitous nature of web servers/API's –Available software to facilitate development –ASCII-based messages improve troubleshooting –Most corporate systems allow such traffic –Easy transition

21. Page 21 Web Services Disadvantages –Potential security holes (HTTP) –Conversion of data structures to SML is computationally expensive; data structure is larger Slower Needs more bandwidth Examples: Apple's Web Objects, IBM Websphere, MS.NET, Sun's Open Net Environment

22. Page 22 Agent-Oriented Applications: financial management, military logistics, personal information management Newest: Intelligent software agents Autonomous, intelligent software entities with ability to perceive environment, reason, act (to accomplish goals) Tend to be implemented as frameworks

23. Page 23 Agent-Oriented Provide for –Interagent communication –Load balancing –Mobility (move agents between machines) May include MOM or Object-Oriented Middleware Examples: HIVE, CMU's RETSINA

24. Page 24 Frameworks Similar to but different from Middleware Targeted at specific domain Provide API, user interface, tools for development & management May provide own middleware services or utilize common ones Examples: Lotus Notes, MS Office, Transarc's Encina, Cognos, HP's OpenView

25. Page 25 Frameworks - Comments Framework vs. Middleware: not standard, debated Author distinguishes: –Middleware: invisible, no interface –Framework - provides interfaces Ubicomp - ubiquitous computing –Numerous initiatives –e.g., Universal plug-and-play

26. Page 26 Middleware Standards Help with functionality, interoperability among implementers Consortiums (IEEE) - compromise, voluntary Corporations - de facto standards; market share, influence e.g., IBM PC; MS Windows

27. Page 27 Standards - Examples COM/DCOM - MS - de facto –Distributed Component Object Model –Communication protocol between objects –IDL - Interface Description Language CORBA - Object Management Group - consortium –Common Object Request Broker Architecture –Powerful, Widely-used –Uses IDL-to-program language mapping for many object-oriented language; generate skeleton & stub code

28. Page 28 Standards - Examples DCE - Open Group –Distributed Computing Environment –Popular, forms basis of many middleware layers –Set of integrated system service specs.; OS, platform, network independent –Provide: RPC, distributed file system, diskless workstation support

29. Page 29 Java Middleware Technologies - Sun Numerous middleware initiatives & support Supports CORBA J. Remote Method Invocation (RMI) - CORBA like J. Message Service (JMS) - provides MOM J. Web Services Developer Pack (WSDP) - to integrate webservices into J. applications J. Servlet & J. Server Pages (JSP) - extend server functionality, dynamic content support J. Jini - adaptive network-centric applications Disadvantage: One source, one language

30. Page 30 Web Service Standards World Wide Web Consortium (WSC) - a leader HTML, HTTP, SML, SOAP/SMLP, WSDL, others Organization for Advancement of Structured Information Standards (OASIS) DocBook (documentation), DSML (directory services), ebXML (eBusiness), SAML (security assertion), UDDI (universal description, discover, & integration of web services)

31. Page 31 Database Standards SQL (Structured Query Language) - Oracle –Based on IBM's SEQUEL of 1970's –de facto standard –Are non-standard extensions ODBC - Open Database Connectivity - MS –middleware database driver: database - applications communication –Vendors: ODBC-compliant database –Sun's JDBC for Javas is ODBC - comp.

32. Page 32 Middleware Design Considerations Complement project, easier to design, develop, & maintain Interoperability, reliability, efficiency throughput Secure, dynamic, adaptable, scalable, available, fault-tolerant Flexible, portable, maintainable, reusable

33. Page 33 Middleware Issues May add unwanted infrastructure to project Risky when using proprietary middleware (if sole source) Extensions: Open Source vs. Proprietary Middleware defined by API & protocols –Be wary of proprietary extensions Shift from OS/Platform dependence to middleware dependence –Projects look to middleware for services

34. Page 34 Middleware Conclusion See 5.6, pg. 119+ for examples Middleware provides variety of services Applicable to Mobile Computing and Smart Environments