Web Engineering

Universitas Gunadarma

Web EngineeringWeb Application Architectures

Dr. Mohammad IqbalThanks to Federico M. Facca

Web Engineering (703512)

Overview

• Introduction• Web Application Architectures• Summary

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INTRODUCTIONWhat is an architecture?

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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

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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

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Developing ArchitecturesInfluences on Architectures

Architecture

Functional Requirements•Clients•Users•Other Stakeholders

Non-Functional Requirements•Performance•Scalability•Reusability•Other?

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Developing ArchitecturesInfluences on Architectures

Technical Aspects•Operating System•Middleware•Legacy Systems•Other?

Architecture

Experience with•Existing Architecture•Patterns•Project Management•Other?

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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?)

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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!

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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

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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.

Framework(Black Box)

Java C# C++ VB.Net

Presentation, business rules, database queries, etc

Company business rules, standards, policies

Object(GUI, XML, data, authentication, etc)

Controlled Environment


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

What is a Framework?


Example Framework

Framework(Black Box)

Java C# C++ VB.Net

Drop Down List, Select * from Users, log fileCompany

business rules, standards, policies Render: Drop Down List of Users on a Web page

or Window Application, recording any errors to the log file

Procedural Application100% complexity

75% complexity 25% complexity


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


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


Presentation Business ObjectsFramework/Web Service

XML

Production/Development

Development

Framework and Web Service Environment

Database


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


WEB APPLICATION ARCHITECTURES

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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

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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

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Example of a WAA

Web Application

Presentation Business Logic Data Management

Personalization Security Search

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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)

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Model View Controller

• Architectural Pattern from Smalltalk (1979)• Decouples data and presentation• Eases the development

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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

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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

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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

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Client/Server (2-Layer)

Client

Web/App Server

Database

Services

Dynamic HTML

Static HTML

Client

Server

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N-Layer Architectures

Client

Application Server(Business Logic, Connectors,Personalization, Data Access)

Presentation Layer

Firewall

Proxy

Web Server

DBMS B2B

Backend(Legacy Application,

Enterprise Info System)

Business Layer

Data Layer

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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

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JSP-Model-1 Architecture

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JSP-Model-2 Architecture

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1. user request2. create/change model3. create/change view4. generate output5. server response


Struts Architecture

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1. user request2. forwarding to controller3. create/change model4. create/change view5. generate output6. server response


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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Web Engineering