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Web Engineering

Web Application Architectures Dr. Mohammad Iqbal Thanks to Federico M. Facca. Web Engineering. Overview. Introduction Web Application Architectures Summary. What is an architecture?. INTRODUCTION. Software Architectures.

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Web Engineering

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  1. Web Application Architectures Dr. Mohammad Iqbal Thanks to Federico M. Facca Web Engineering

  2. Overview • Introduction • Web Application Architectures • Summary

  3. What is an architecture? INTRODUCTION

  4. Software Architectures • “Architecture is defined [...] as the fundamental organization ofa system, embodied in its components, their relationships to each other and the environment, and the principles governing its design and evolution.”(IEEE Architecture Working Group, P1471, 1999) • Architectures describe structure • Components of software systems, their interfaces and relationships • static as well as dynamic aspects • blueprint of software system • Architectures connect software development phases • requirements mapped iteratively to components and their relationships

  5. Software Architectures • “Architecture is the set of design decisions [...] that keeps its implementers and maintainers from exercising needless creativity.”(Desmond F. D’Souza and Alan C. Wills, 1999) • Architectures describe different viewpoints • conceptual view: entities of application domain and their relationships • process view: system runs, concurrency, synchronization • implementation view: software artefacts (subsystems, components, source code) • runtime view: components at runtime and their communication • Architectures make systems comprehensible and controllable • structuring according to different viewpoints • enables communication between different stakeholders

  6. Developing ArchitecturesInfluences on Architectures • Functional Requirements • Clients • Users • Other Stakeholders • Non-Functional Requirements • Performance • Scalability • Reusability • Other? Architecture

  7. Developing ArchitecturesInfluences on Architectures • Technical Aspects • Operating System • Middleware • Legacy Systems • Other? Architecture • Experience with • Existing Architecture • Patterns • Project Management • Other?

  8. Developing Architectures • Remember, requirements are always subject to change. • Organizational & Environment changes • Ambiguous requirements initially • Thus, iterative approaches are the suggested means of development • Pro: Helps to mitigate design risks • Caution: Doesn’t guarantee a good architecture (ex., What about legacy systems?)

  9. Patterns & Frameworks • Patterns describe recurring design problems • 3 types of patterns • Architecture patterns (e.g. MVC) • Design patterns (e.g. Publisher-Subscriber) • Idioms (e.g. Counted-Pointer in C++) • They are a guideline, implementation must be grounded to the specific problem • Patterns need to be “integrated” among them!

  10. Patterns & Frameworks • Frameworks: another option to reuse existing architecture • something that provides you a frame to be filled! • Reuse of existing software objects that just need to be properly configured • Bound to a specific technology • Require training • High cost of switch • Level of customization not always accetable

  11. Framework (Black Box) Java C# C++ VB.Net What is a Framework? • Framework is a group of components that work interactively with requests from other components or objects to generate a consistent output. Presentation, business rules, database queries, etc Company business rules, standards, policies Object (GUI, XML, data, authentication, etc) Controlled Environment

  12. What is a Framework? For example, in order for a program to get data from a mysql database, it has to undergo a list of actions: 1. Connect to the database server 2. Select a database 3. Query the database 4. Fetch the data 5. Use the Data A framework may handle steps 1-4 for you, so that your responsibilities are reduced to: 1. Tell the framework to fetch the data 2. Use the data

  13. Framework (Black Box) Java C# C++ VB.Net Example Framework Drop Down List, Select * from Users, log file Company business rules, standards, policies Render: Drop Down List of Users on a Web page or Window Application, recording any errors to the log file 75% complexity 25% complexity Procedural Application 100% complexity

  14. Benefits of a Framework • Consistency across many platforms • Better able to enforce standards and policy • Better way to reuse components • Lower skilled employee can perform work more efficiently • Single point of change to a common interface • Produce applications that are more robust, faster, stable and consistent

  15. Implementing Framework: Web Services • A web service is a component that is presented as a URL that returns the desired information or objects • Web services are built the same way as class objects • Using a web service • Add a web reference • Add applicable XML documents • Call the web service through a URL, passing the necessary parameters • Process the information or object returned

  16. Framework and Web Service Environment Framework/ Web Service Presentation Business Objects Database XML Production/ Development Development

  17. Web application frameworks • Many frameworks are being developed… • JavaServer Faces, Struts, Webwork2 • WebObjects (.NET specific) • Model Glue (ColdFusion specific) • Velocity, Fusebox, Mach II, Maypole, Catalyst, Tapestry, ZNF, Phrame, Cocoon, Ruby on Rails, … • Most, but not all, are based around M-V-C

  18. Web APPLICATION Architectures

  19. Architecture Types • Layering Aspect • “Separation of concerns” • How many concurrent users are you serving? • Shared needs among multiple applications? (e.g., security) • Data Aspect • What kind(s) of data are you delivering? • Structured vs. non-structured • On-demand vs. real-time • What are the bandwidth requirements? • Size & nature of data • Again, audience concerns

  20. Architecture Types • Web Platform Architecture (WPA) • Platform = Infrastructure • Hardware • Software modules & configurations • Choice of software platform (e.g., J2EE, .NET) • Web Application Architecture (WAA) • Conceptual view of how key business processes and needs are separated & implemented • Often domain-specific • Greater complexity requires greater modularity

  21. Example of a WAA Web Application Presentation Business Logic Data Management Personalization Security Search

  22. Generic Web (Platform) Architecture • The Web “platform” is based on • TCP/IP • HTTP • HTML • It’s essentially a Client/Server architecture! • In term of patterns one of the simplest one • But still thing can get complex… • Components on the network (firewall, proxy, load balancer) • Components in the intranet (Web server, application server, data base, legacy systems, web services)

  23. Model View Controller • Architectural Pattern from Smalltalk (1979) • Decouples data and presentation • Eases the development

  24. Model View Controller • Model • encapsulate application state • responds to state queries • exposes application functionality • notifies views of changes • View • renders the models • requests updates from models • sends user interaction to controller • allows controller to select view • Controller • defines application behavior • maps user actions to model updates • selects view for response • one for each functionality

  25. Web Architectures: Specifics • Technological constraints • HTTP • Broad variety of technical solutions • application servers, proxies, firewalls, legacy applications • checking of quality difficult • e.g., performance depends on various components, like database, network bandwidth, processor, memory, code, … • improvement of quality difficult • e.g., code performance may not change overall performance substantially • Technical solutions inhomogeneous and immature • short product life cycles • missing standards impede component integration from different manufactures • many solutions are open source: continuity of development, extendibility, … • Global access to Web applications • internationalization, cultural differences

  26. Model-View-Controller 2 (MVC 2) • Adaptation of MVC for the Web • stateless connection between the client and the server • notification of view changes • re-querying the server to discover modification of application’s state

  27. Client/Server (2-Layer) Client Client Server Web/App Server Services Database Dynamic HTML Static HTML

  28. N-Layer Architectures Client Firewall Proxy Presentation Layer Web Server Business Layer Application Server (Business Logic, Connectors, Personalization, Data Access) Backend (Legacy Application, Enterprise Info System) Data Layer DBMS B2B

  29. Why an N-Layer Architecture? • Separating services in business layer promotes re-use among applications • Loose-coupling – changes reduce impact on overall system. • More maintainable (in terms of code) • More extensible (modular) • Trade-offs • Needless complexity • More points of failure

  30. JSP-Model-1 Architecture

  31. JSP-Model-2 Architecture 1. user request 2. create/change model 3. create/change view 4. generate output 5. server response

  32. Struts Architecture 1. user request 2. forwarding to controller 3. create/change model 4. create/change view 5. generate output 6. server response

  33. Things to keep in mind(or summary) • Good design of architecture is crucial • You can leverage on patterns and frameworks • Both have advantages and disadvantages • Design is constrained on Web “infrastructure” • MVC is the most commonly used pattern

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