Application Architecture

1
Application Architecture
2
Application Architecture

• Application architecture a specification of the
  technologies to be used to implement information
  systems
• Data architecture.
• Component architecture.

3
Component Architecture

• Distributed system a system in which components
  are distributed across multiple locations and
  computer networks.
• Accordingly, the processing workload is
  distributed across multiple computers on the
  network.
• Centralized systems a system in which all
  components are hosted by a central, multi-user
  computer.
• Users interact with the system via terminals (or
  a PC emulating a terminal).
• Virtually all the actual processing and work is
  done on the host computer.

4
Why the Trend Toward Distributed Systems?

• Modern businesses are already decentralized
  (distributed).
• Distributed computing moves information and
  services closer to the customers and users who
  need them.
• Distributed computing consolidates the power of
  personal computers across the enterprise.
• Distributed computing solutions are in general
  more user-friendly because they use the PC as the
  user interface processor.
• Personal computers and network servers are less
  expensive than mainframe computers

5
Data Architectures

• Relational database stores data in tabular form.
  Each file is implemented as a table. Each field
  is a column in the table.
• Distributed relational database A database
  system that duplicates tables to multiple
  database servers located in geographically
  distributed locations.

6
Centralized Database
7
Centralized Database

• All data is stored in a single database
• Advantages
• Concurrency and data integrity
• Good for systems with large amounts of constantly
  changing data
• Disadvantages
• A central repository can easily become a
  bottleneck
• Single point of failure

8
Types of Data(base) Distribution

• Data partitioning truly distributes rows and
  columns of tables to specific database servers
  with little or no duplication between servers.
• Vertical partitioning assigns different columns
  to different servers.
• Horizontal partitioning assigns different rows to
  different servers.
• Data replication duplicates some or all tables
  on more than one database server.
• Propagates updates on one database server to any
  other database server where the data is
  duplicated.

9
Data Partitioning
10
Data Replication
11
Data Partitioning versus Data Replication
12
Software Architectural Styles

• Patterns for software architecture
• File Server
• Client-Server
• Peer-To-Peer
• Model/View/Controller
• Pipes and Filters
• And more domain specific architectures

13
File Server

• File Server A computer attached to a network
  that has the primary purpose of providing a
  location for the shared storage of computer files
  (such as documents, sound files, photographs,
  movies, images, databases, etc.)
• File server sends the clients entire files or
  database table without processing it.

14
File Server
15
File Server

• File server system a LAN (local Area Network)
  in which a server hosts the data of an
  information system.
• All other layers are implemented on the client
  computers.
• Frequently excessive network traffic to transport
  data between servers and clients.
• Client must be fairly robust (fat) because it
  does most of the work.

16
File Server Architecture
17
Client/Server Architectural Style

• One or many servers provides services to
  instances of subsystems, called clients.
• Client calls on the server, which performs some
  service and returns the result
• Response in general immediately
• Users interact only with the client
• Sometimes called two-tiered client/server
  computing.

18
Client/Server Architectural Style
19
Client/Server Database

• Client Server Database a client/server system in
  which the data and data manipulation layers are
  placed on the server(s), and other layers are
  placed on the clients.
• Difference to file server systems is where the
  data manipulation commands are executed.
• Much less network traffic than file server
  systems because only the database requests and
  the results of those requests are transported
  across the network.
• Database integrity is easier to maintain.

20
Client/ServerDistributed Data
21
Client/Server Architectural Style

• Advantages
• Loose coupling between the server and client
• Disadvantages
• Dependability when server goes down, operations
  cease

22
Client/Server Architecture Servers

• Database server a server that hosts one or more
  databases and executes all data manipulation
  commands at the server.
• Transaction server a server that hosts services
  which ensure that all database updates for a
  transaction succeed or fail as a whole.
• Application server a server that hosts
  application logic and services for an information
  system.
• Messaging or groupware server a server that
  hosts services for e-mail, calendaring, and other
  work group functionality.
• Web server a server that hosts Internet or
  intranet websites.
• Remote Procedure Call

23
Internet- and Intranet-based Architectures

• Network computing system presentation and
  presentation logic layers implemented in
  client-side Web browsers using content downloaded
  from a Web server.
• Presentation logic layer connects to application
  logic layer running on application server, which
  connects to database servers on the backside of
  the system.
• The greatest potential of this approach is its
  applicability to redesign of traditional
  information systems to run on an intranet.
• Intranet a secure network that uses Internet
  technology to integrate desktop, work group, and
  enterprise computing into a cohesive framework.

24
Peer-to-Peer Architectural Style

• Generalization of Client/Server Architecture
• Clients can be servers and servers can be clients

25
Peer-to-Peer Architectural Style

• Examples
• Distributed computing
• Distributed search engine
• Advantage
• Scalability
• Reliability
• Disadvantage
• Concurrency/deadlock issue

26
Three Tiered Architectural Style

• Three layers are organized as follows
• Interface Layer User interface, user object
  control
• Windows, forms, web pages, etc
• Application logic layer Control over objects and
  data processing
• Rule checking
• Storage layer Database abstraction
• Any persistent objects are managed

27
Three Tiered Architectural Style

• Developed as an analog to the repository
  architecture
• Allows the development of many user interfaces
  for the same application logic layer
• Allows the development of many application logic
  layers to operate on the same storage layer

28
Three Tiered Architectural Style
29
Three Tiered Architectural Style
30
Four Tiered Architectural Style

• The interface layer is subdivided into two
  independent layers
• Client presentation layer
• Implements the end user interface reuses common
  presentation objects and operations from the
  server
• Server presentation layer
• Can be located on many machines, reducing the
  possibility of a bottleneck

31
Four Tiered Architectural Style
32
Model/View/Controller

• Subsystems are classified into 3 different types
• Model Responsible for application domain
  knowledge
• View Responsible for displaying application
  domain objects to the user
• Controller Responsible for sequence of
  interactions with the user.

33
Example of a File System Based on the MVC
Architectural Style
34
Model View Controller Example

• Java Server Page

35
Model View Controller Example

• Java Server Page

36
Pipe and Filter Architectural Style

• Subsystems are referred to as filters
• Interactions between subsystems are called pipes
• Each filter is only aware of the content of the
  data it will receive, not the filter that sent
  the data
• Examples
• Linux shell pipes
• Graphic and video filters

37
Pipe and Filter Architectural Style

• Advantages
• Loosely coupled
• Filters may be interchanged or substituted for
  another
• Good for systems that apply systematic
  transformations to data without user intervention
• Disadvantages
• Poorly suited for interactive systems
• Does not allow complex interactions between
  components

38
Pipe and Filter Architectural Style
39
Domain Specific Architecture Styles

• Main program/subroutine organizations
• Concurrent state machine
• Real time process, more information can be found

40
Architecture Case Study KWIC

• Problem description
• The KWIC Key Word in Context index system
  accepts an ordered set of lines, each line is an
  ordered set of words, and each word is an ordered
  set of characters. Any line may be circularly
  shifted' by repeatedly removing the first word
  and appending it at the end of the line. The KWIC
  index system outputs a listing of all circular
  shifts of all lines in alphabetical order.

41
KWIC example

• Input
• Pattern-Oriented Software Architecture
• Software Architecture
• Introducing Design Patterns
• Output (assuming Pattern-Oriented treated as one
  word)
• Architecture Software
• Architecture Pattern-Oriented Software
• Design Patterns Introducing
• Introducing Design Patterns
• Patterns Introducing Design
• Pattern-Oriented Software Architecture
• Software Architecture
• Software Architecture Pattern-Oriented

42
Main Program/Subroutine with Shared Data
43
Main Program/Subroutine with Shared Data

• Strengths
• Efficient use of space - computations share same
  data
• Weaknesses
• Change of data representation affects all modules
  all modules take advantage of explicit data
  representation - no information hiding.
• Not particularly supportive of reuse - explicit
  references to data structures and other
  functions. Tight coupling.

44
Abstract Data Type (OO)
45
Abstract Data Type (OO)

• Key Difference Data not directly shared - data
  accessed only through module interfaces.
• Strengths
• Data representations can be changed inside
  individual modules without affecting others.
• Reuse better supported because modules make less
  assumptions about others - looser coupling.
• Weaknesses
• Larger storage is needed.

46
Pipe and Filter
47
Pipe and Filter

• Strengths
• Supports enhancements by addition of filters e.g.
  an omit noisy shift filter, or by modifying
  independent filters.
• Supports reuse, filters operate in isolation.
• Weaknesses
• Inefficient use of space. For example, each
  filter must copy all of the data to its output.

48
Middleware

• Middleware utility software that enables
  communication between different processors in a
  system.
• It may be built into the respective operating
  systems or added through purchased middleware
  products.
• Presentation middleware
• Application middleware
• Database middleware

49
Middleware
50
Reading Assignment

• Textbook Chapter 13