Building Desktop Applications with Web Services in a Message-based MVC Paradigm by Xiaohong Qiu Ph.D. student of EECS department, Syracuse University Research work is performed at Community Grids Lab, Indiana University email@example.com, firstname.lastname@example.org 501 Morton N. St, Suite 222, Bloomington IN 47404 CommunityGrids Lab, Indiana University
Background • CGL research– general 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)
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.
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
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
Our approach • Building applications centered on messages • Separation of application architecture from messaging infrastructure • Message-based MVC Paradigm fordistributed, Web, and desktop applications • MMVC and MVC • MMVC and Web Services • MMVC and collaboration • MMVC and messaging infrastructure
Related technologies • Batik SVG browser (an open source project from Apachethat 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
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.
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
Model View Controller Decomposition of SVG Browser Semantic Model Events as messages Rendering as messages Controller High Level UI Input port Output port View Events as messages Rendering as messages Raw UI Display Display Messages contain control information a. MVC Model b. Three-stage pipeline Figure 1 Reformulation of SVGto message based MVC in a Web Service Model A comparison of MVC and MMVC model in a case of SVG application
Collaborative SVG Chess Game Players Observers
R R R Master client SVG browser 1 Other client SVG browser 2 Other client SVG browser n XGSP Session control Server F F F I I I NaradaBrokering Event (Message) Service Infrastructure O O O Control to/from all SVG browsers in the collaborative session Data from master client Data from master client Control to/from XGSP Control to/from XGSP • • • Figure 3 Architecture of collaborative SVG browser on PC Data to other clients Control to/from XGSP Architecture of collaborative SVG browser on PC
NaradaBrokering Event (Message) Service Infrastructure XGSP Session control Server Control to/from Control to/from SVG WS1,2, …, n SVG WS1,2, …, n SVG WS 1 SVG display 2 SVG display n SVG display 1 Rendering to SVG display 2 Rendering from SVG WS 2 SVG WS 2 Control to/from SVG display 2 Control to/from XGSP, SVG display 2 • • • • • • SVG WS n Internet Game Figure 4 Architecture of collaborative Web Services drawn for particular case of Internet multiplayer game with SVG Architecture of multiplayer game with SVG
Collaborative events (e.g. Master Events which has context information of collaboration and information from previous stages) 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) Figure 5 Collaborative SVG Event processing chart Collaborative SVG Event processing chart
Method-based MVC vs. message-based MVC Broker Set up an event class (topic) Subscribe to event class Send event publish an event class register call back method B A A B invoke call back method with event method based message based
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.
Broker Broker subscribe subscribe publish publish send event A send event A B A B View Shared state Separated component/service model Conventional shared state model Implicit State
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.
Performance TestingT1: A given user event such as a mouse click can generate multiple associated DOM change events transmitted from the Model to the View. T1 is the arrival time at the View of the first of these.T2: This is the arrival of the last of these events from the Model and the start of the processing of the set of events in the GVT treeT3: This is the start of the rendering stageT4: This is the end of the rendering stage
Performance Results Table 1 Timing of Stages in milliseconds
Shared SVG Browser on PC Shared SVG Browser on PDA Internet Game Event (Message) Service Event (Message) Service Event (Message) Service Collaborative Events and Web Service messages Collaborative Events and Web Service messages Collaborative Events and Web Service messages R F I O R F I O Web Service Web Service R F I O Semantic Semantic High Level UI U F I O SVG Browser Input port Output port U F I O Semantic High Level UI Raw UI Display Rendering as messages Events as messages Input port Output port Rendering as messages Events as messages High Level UI Raw UI Display Raw UI Display Messages contain control information Messages contain control information Messages contain control information a. Non-decomposed collaborative SVG requiring minimal changes to the original source code b. Decomposed WS optimized for thin clients c. Decomposed WS optimized for performance Figure 2 Three among the different ways of decomposing SVG between client and Web Service component Three among the different ways of decomposing SVG between client and Web Service component
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
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.
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
Future Work • Performance analysis • Performance optimization • Apply the concept to other applications (e.g. OpenOffice)
References • Community Grids Lab • University Web sitehttp://www.communitygrids.iu.edu/ • CGL Web sitehttp://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