Web Engineering
Web Application Architectures
Dr. Mohammad Iqbal
Thanks to Federico M. Facca
Universitas Gunadarma
Overview
• Introduction
• Web Application Architectures
• Summary
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What is an architecture?
INTRODUCTION
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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 Architectures
Influences on Architectures
Functional Requirements
•Clients
•Users
•Other Stakeholders
Architecture
Non-Functional Requirements
•Performance
•Scalability
•Reusability
•Other?
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Developing Architectures
Influences 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)
Company
business
rules,
standards,
policies
Java
C#
C++
VB.Net
Presentation,
business rules,
database queries,
etc
Object
(GUI, XML, data, authentication, etc)
Controlled Environment
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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
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Example Framework
Framework
(Black Box)
Company
business
rules,
standards,
policies
Java
C#
C++
VB.Net
Drop Down List,
Select * from
Users, log file
Render: Drop Down List of Users on a Web page
or Window Application, recording any errors to the log file
75% complexity
Procedural Application
100% complexity
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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
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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
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Framework and Web Service Environment
Presentation
Business Objects
Framework/
Web Service
Database
XML
Production/
Development
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Development
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
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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
Personalization
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Business Logic
Security
Data Management
Search
21
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
Client
Server
Web/App Server
Services
Database
Dynamic HTML
Static HTML
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N-Layer Architectures
Client
Firewall
Proxy
Web Server
Presentation Layer
Business Layer
Application Server
(Business Logic, Connectors,
Personalization, Data Access)
Backend
(Legacy Application,
Enterprise Info System)
Data Layer
DBMS
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B2B
28
Why an N-Layer Architecture?
• Separating services in business layer promotes reuse 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
1. user request
2. create/change model
3. create/change view
4. generate output
5. server response
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Struts Architecture
1. user request
2. forwarding to controller
3. create/change model
4. create/change view
5. generate output
6. server response
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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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