![Ph.D. student of EECS department, Syracuse University Research work is performed at Community Grids Lab, Indiana University [email_address] , [email_address] 501 Morton N. St, Suite 222, Bloomington IN 47404 Community Grids Lab, Indiana University by Xiaohong Qiu Web Service Architecture for e-Learning July 23, 2004](https://image.slidesharecdn.com/web-service-architecture-for-elearning1825/85/Web-Service-Architecture-for-e-Learning-1-320.jpg)
Web Service Architecture for e-Learning
- 1. Ph.D. student of EECS department, Syracuse University Research work is performed at Community Grids Lab, Indiana University [email_address] , [email_address] 501 Morton N. St, Suite 222, Bloomington IN 47404 Community Grids Lab, Indiana University by Xiaohong Qiu Web Service Architecture for e-Learning July 23, 2004
- 2. Background CGL research – g eneral area is technology support for Synchronous and Asynchronous Resource Sharing e-learning e-science Grids manage and share (typically asynchronously) resources (people, computers, data, applications etc.) or distributed services in a centralized fashion. Web Services Define loosely coupled software components across internet interacting with messages. Peer-to-peer Grids link services, resources and clients in dynamic decentralized fashion The system consists of a sea of message-based Services (e.g. shared SVG as a Web Service) Services linked by publish-subscribe messaging infrastructure (e.g. NaradaBrokering)
- 3. Current projects of CGL NSF Middleware Initiative (NMI) CGL, Extreme Lab of IU, University of Texas, University of Chicago, Argon National Lab, a suite of grid services including portlets interface for middleware environment NaradaBrokering A open source messaging infrastructure/middleware for collaboration, peer-to-peer, and Grid applications collaboration environments GlobalMMCS A open source multimedia collaboration system (multiple video conferencing technology that supports Java A/V, H323, real player clients; XGSP session control) Collaborative SVG, PowerPoint, and OpenOffice etc.
- 4. Research on a generic model of building applications Applications: distributed, Web/Internet, desktop motivations CPU speed (Moore’s law) and network bandwidth (Gilder’s law) continue to improve bring fundamental changes Internet and Web technologies have evolved into a global information infrastructure for sharing of resources Applications getting increasingly sophisticated, e.g. Internet collaboration enabling virtual enterprises; large-scale distributed computing) Requires new application architecture that is adaptable to fast technology changes with properties scalability Reusability Interoperability Reliability High performance Low cost
- 5. Summarization of the situation The subsystem of Internet has evolved into stability TCP/IP network stack dominating the communication protocol domain; IP forms the low-level sphere surrounding hardware network core Construction of distributed operating system over the Internet has not completed and keeps adding new functionalities to the general purpose platform One current effort focuses on building of messaging infrastructure tailored for disparate applications Evolution of application architectures client-server model Multi-tier (e.g. three-tier) model Peer-to-peer A variety of distributed model (e.g. Java RMI, CORBA, COM/DCOM, J2EE, .NET) Grids Web Services and SOA Web application deployment shows diverse directions but have common features User interfaces Services for the sharing of information and resources (e.g. through unicast and multicast of group communication) In the most general sense, collaboration is the core problem and service of Web applications, although “collaboration” usually refers to system with real-time synchronous and compelling time constraints Next generation of Web client should enable pervasive accessibility Ubiquitous availability to clients fro heterogeneous platforms (e.g. Windows, Linux, Unix, and PalmOS) Uniform Web interface that provides a platform with aggregation of multiple services
- 6. Physical network Virtual distributed operating system Messaging infrastructure Application Network system in a layered stack Same layer ?
- 7. NaradaBrokering One can bind SOAP to NaradaBrokering and allow use of any of NaradaBrokering transport NaradaBrokering is placed in SOAP handler and controls transport, security and reliable messaging using WS-Security and WS-Reliable Messaging For a stream, one first uses port 80 and conventional SOAP over HTTP and then negotiates the transport and encoding to be used in messages of the stream
- 8. Architecture of publish/subscribe model based on NaradaBrokering event broker notification service
- 9. Our approach Building applications centered on messages Separation of application architecture from messaging infrastructure Focus on exploration in design space and study system composition and interaction. Event models and Publish/Subscribe scheme Message-based MVC Paradigm for distributed, Web, and desktop applications MMVC and MVC MMVC and Web Services MMVC and collaboration MMVC and messaging infrastructure
- 10. Related technologies Batik SVG browser (an open source project from Apache that supports SVG 1.0) A presentation style application is representative and complex in nature (we experiments with multiplayer-online game with high interactivity and compelling time constraints) Similar applications includes Microsoft PowerPoint, Adobe Illustrator, Macromedia Flash SVG (W3C specifications for Scalable Vector Graphics) A language for describing 2D vector and mixed vector/raster graphics in XML. DOM (W3C specifications for Document Object Model) Programmatic interfaces for access and manipulate structured document object All modern browsers (approximately) support the W3C DOM
- 11. Methodology Proposing an “ explicit Message-based MVC ” paradigm (MMVC) as the general architecture of Web applications Demonstrating an approach of building “ collaboration as a Web service ” through monolithic SVG experiments . As an example, we present architecture for three types of collaboration ─ monolithic, thin client, and interactive client. Bridging the gap between desktop and Web application by leveraging the existing desktop application with a Web service interface through “ MMVC in a publish/subscribe scheme ”. As an experiment, we convert a desktop application into a distributed system by modifying the architecture from method-based MVC into message-based MVC. Proposing Multiple Model Multiple View and Single Model Multiple View collaboration as the general architecture of “ collaboration as a Web service ” model. Identifying some of the key factors that influence the performance of message-based Web applications especially those with rich Web content and high client interactivity and complex rendering issues.
- 12. What is message-based MVC? Message-based Model-View-Controller (MMVC) is a general approach of building applications with a message-based paradigm emphasizes a universal modularized service model with messaging linkage Converges desktop application, Web application, and Internet collaboration MVC and Web Services are fundamental architecture from desktop to Web applications, MMVC has general importance as a uniform architecture MMVC allows automatic collaboration, which simplifies the architecture design
- 13. MVC paradigm
- 14. SMMV vs. MMMV as MVC interactive patterns
- 15. Monolithic collaboration model NaradaBrokering Identical programs receiving identical events master SVG browser client master master SVG browser client other master SVG browser client other master SVG browser client other
- 16. SVG DOM Model as Web Service NaradaBrokering SMMV collaborative Web Service model Share output port master SVG client master View master SVG client other View master SVG client other View master SVG client other View
- 17. MMMV collaborative Web Service model Share input port NaradaBrokering master SVG client master View master SVG client other View master SVG client other View master SVG client other View Broker SVG DOM Model as Web Service SVG DOM Model as Web Service SVG DOM Model as Web Service SVG DOM Model as Web Service Broker Broker Broker
- 18. A comparison of MVC and MMVC model in a case of SVG application Model View Controller a. MVC Model Controller View Display Model Messages contain control information Decomposition of SVG Browser b. Three-stage pipeline High Level UI Raw UI Display Rendering as messages Events as messages Semantic Events as messages Rendering as messages Figure 1 Reformulation of SVG to message based MVC in a Web Service Model Input port Output port
- 19. Method-based MVC vs. message-based MVC B Subscribe to event class A Broker Set up an event class (topic) publish an event class Send event message based A B register call back method invoke call back method with event method based
- 21. Three among the different ways of decomposing SVG between client and Web Service component Shared SVG Browser on PDA b. Decomposed WS optimized for thin clients Rendering as messages Events as messages Messages contain control information Semantic High Level UI R F I O U F I O Web Service Event (Message) Service Raw UI Display Shared SVG Browser on PC a. Non-decomposed collaborative SVG requiring minimal changes to the original source code Messages contain control information Event (Message) Service R F I O SVG Browser Semantic High Level UI Raw UI Display Collaborative Events and Web Service messages Internet Game c. Decomposed WS optimized for performance Messages contain control information Semantic R F I O U F I O Web Service Event (Message) Service High Level UI Raw UI Display Figure 2 Three among the different ways of decomposing SVG between client and Web Service component Input port Output port Rendering as messages Events as messages Input port Output port Collaborative Events and Web Service messages Collaborative Events and Web Service messages
- 22. Monolithic SVG Experiments Collaborative SVG Browser Teacher-Students scenario Static Shared SVG contents Dynamic Share SVG contents Hyperlink Interactivity and animation (JavaScript binding) Collaborative SVG Chess game Two players-multiple observers scenario Complex interactivity with game intelligence
- 23. Collaborative SVG Chess Game Players Observers
- 24. Collaborative SVG Event processing chart Figure 5 Collaborative SVG Event processing chart Raw UI events (e.g. Mouse and key events) High Level UI events (e.g. SVG/DOM events) Semantic events (e.g. Application events such as “capture” in chess game) Collaborative events (e.g. Master Events which has context information of collaboration and information from previous stages)
- 25. The general event/listener model Component A (Event Source) Component B (Event Listener) register for event notification issue event occurrence
- 26. Java delegation event model Event Source register event x listeners Invoke call back method with event x x EventListener 1 x EventListener 2 x EventListener n
- 27. Topic-based Publish/subscribe model Subscriber 1 Subscriber 2 Subscriber 3 Subscriber 4 Subscriber 5 Publisher 1 Publisher 2 Topic A Topic B Topic C broker broker broker broker Notification Service
- 28. Subscribe to event class Broker Set up an event class (topic) publish an event class Send event Component A Component B Figure2 Event-driven message-based Publish/Subscribe scheme Figure3 Shared Input Port of Collaborative SVG Broker Input port Output port View GVT Renderer User Port JavaScript SVG DOM Application as Web Service Port Facing Resource Rendering as messages Event as messages Model Master client Set up an event class (topic) Publish an event to collaborative clients Subscribe to the topic Facing Input port Output port View GVT Renderer User Port JavaScript SVG DOM Application as Web Service Port Resource Rendering as messages Model Participating client Facing Facing Facing
- 29. Architecture of monolithic collaborative SVG Figure 3 Architecture of collaborative SVG browser on PC XGSP Session control Server NaradaBrokering Event (Message) Service Infrastructure • • • Master client SVG browser 1 F I R O Other client SVG browser 2 F I R O Other client SVG browser n F I R O Control to/from all SVG browsers in the collaborative session Data from master client Control to/from XGSP Data to other clients Control to/from XGSP Data from master client Control to/from XGSP
- 30. Architecture of multiplayer game with SVG Figure 4 Architecture of collaborative Web Services drawn for particular case of Internet multiplayer game with SVG NaradaBrokering Event (Message) Service Infrastructure • • • XGSP Session control Server SVG WS 1 Internet Game SVG WS 2 SVG WS n • • • SVG display 1 SVG display 2 SVG display n Control to/from SVG WS1,2, …, n Control to/from XGSP, SVG display 2 Rendering to SVG display 2 Control to/from SVG WS1,2, …, n Rendering from SVG WS 2 Control to/from SVG display 2
- 31. Decomposition of SVG browser into stages of pipeline
- 32. Important principals One should split at points where the original method based linkage involved serializable Java objects. Serialization is needed before the method arguments can be transported and this is familiar from Java RMI. “ Spaghetti” classes implied that additional state information would need to be transmitted if we split at points where classes spanned interfaces from different modules. Batik often involved large classes that implemented many different interfaces. These interfaces often came from different parts of the program and crossed the possible stages mentioned above. message-based paradigm tends to force a more restrictive programming model where all data is shared explicitly and not implicitly via interfaces crossing splitting lines.
- 33. Implicit State subscribe A B Broker publish send event Separated component/service model subscribe A View B Broker publish send event Conventional shared state model Shared state A
- 34. The changes bring up issues that cause a challenge to the system Timing becomes a compelling issue with the separation of client and Web Service server, original assumption and design principle break since time scope drastically increases from tens of microsecond level (e.g. a Java method call) to a few milliseconds level (network latency plus system overhead). Object serialization is a must have toolkit messages, as a linkage vehicle, contains component information from both sides and keep context same. Synchronization is a factor to consider for context consistency.
- 35. Summary of message-based MVC Provision of a universal paradigm with a service model converging desktop applications, Web applications, and Internet collaboration Web applications built on messages can achieve important features such as scalability The message-based approach is an indispensable part of the big picture of system design with a separate intermediate messaging layer Reduce deployment overhead of applications Increase portability of application by decoupling application architecture with underlying platforms It conforms to service oriented architecture with loosely coupled messages linkage, which we expect to have an increasingly important role for reusability, interoperability, and scalability
- 36. Future Work Performance analysis Performance optimization Apply the concept to other applications (e.g. OpenOffice)
- 37. References Community Grids Lab University Web site http://www.communitygrids.iu.edu/ CGL Web site http://www.infomall.org Additional Projects http://grids.ucs.indiana.edu/ptliupages/ Publications http://grids.ucs.indiana.edu/ptliupages/publications/ CGL activities summary (2003-2004) http://grids.ucs.indiana.edu/ptliupages/publications/CGLHandout.pdf Current major projects of CGL NSF Middleware Initiative (NMI) at www.OGCE.org NaradaBrokering at www.NaradaBrokering.org Collaboration environments GloblaMMCS at http://www.globalmmcs.org/ Commercial product: Anabas at www.anabas.com Collaborative SVG at www.svgarena.org
- 38. Observations The overhead of the Web service decomposition is not directly measured in this table although the changes in T1-T0 in each row reflect the different network transit times as we move the server from local to organization locations. This client to server and back transit time is only 20% of the total processing time in the local examples. We separately measured the overhead in NaradaBrokering itself which consisting of forming message objects, serialization and network transit time with four hops (client to broker, broker to server, server to broker, broker to client). This overhead is 5-15 milliseconds depending on the operating mode of the Broker in simple stand-alone measurements. The contribution of NaradaBrokering to T1-T0 is larger than this (about 30 milliseconds in preliminary measurements) due to the extra thread scheduling inside the operating system and interfacing with complex SVG application. We expect the main impact to be the algorithmic effect of breaking the code into two, the network and broker overhead, thread scheduling from OS.