From Model to Implementation II

Arab Open University
2nd
Semester, 2006-2007
M301
Unit 5.2
From Model to
Implementation
reem.attas@arabou.org.sa

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Topic Road Map
 Components and Component Based
Development
Architectures, frame works and product
lines
Patterns

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Component
A reusable or replaceable piece of
software.
The components would have to be
precisely specified in terms of their
interfaces and the functions they carried
out.

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Kinds of Interfaces
Provided Interfaces: provided by a
component for use by other components
 shown as sockets.
Required Interfaces: required from other
components for use by the component 
shown as plugs.

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Components and their Interconnection

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Object-oriented Components in Java
Components are represented as classes.
A component is able to provide a single
provided interface, but required interfaces
do not need to be made explicit.

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Forms of Inheritance
1. Specialization.
2. Specification.
3. Construction.
4. Extension.
5. Limitation.
6. Combination.

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Java Classes as Components
Classes give encapsulation and
information hiding, with the provided
interface being very explicit.

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To be Able to Reuse Java Classes:
1. Java classes need to be self-describing.
2. The development environment should include
library facilities for storing reusable classes,
with good search facilities to find classes of
potential use.
3. The development environment should contain
easy ways of incorporating an existing
component into an emerging design, making
the connections as required.

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… To be Able to Reuse Java Classes:
4. Persistence, the ability for Java objects and
their states to be preserved over long periods
of time, perhaps as parts of a database.
5. Distribution, the ability of Java objects to
communicate with other objects when
distributed over many processors connected
together by communication networks.

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JavaBeans
Are Java classes that have been provided
with the previous five capabilities in
particular well-defined ways.

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Enterprise JavaBeans have more
facilities:
1. There are separate interface ‘views’ for users of the
EJB components.
2. There are two types of persistence:
1. Session persistence: occurs when software is executed for a
short time, and the EJB persists just for the duration of this
session.
2. Entity persistence: occurs when the EJB persists over many
sessions, even permanently, closely associated with the
database — hence the name ‘entity’, since it is independent of
the execution of the software.
3. There are containers that control the creation and
execution of EJBs.

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How are components supposed to be
used?
 A repository of useful components was built.

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Difficulties with Component Reuse
 Human factor:
 People may mistrust software developed by someone
else.
 People enjoy developing their own software.
 Organizational factor:
 The projects are judged by the success of the project
itself not by the ability to be reused.
 Many organizations think that reuse looks like laziness.

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Topic Road Map
Components and Component Based
Development
 Architectures, frame works and product
lines
Patterns

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Software Architecture
Software architecture is a high-level
abstract description of the structure of a
software system — its major parts and
how they are interrelated.

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Architectural Styles
Software is viewed as a system composed
of a number of subsystems, perhaps of
different types, that are connected
together.
The way the subsystems interact and are
connected together distinguishes the
styles.

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… Architectural Styles
1. Data-flow:
 Support reuse and modifiability.
 Focuses on the flow of data through the system.
 common in older batch computer systems & UNIX.
2. Data-centered:
 Support the ability to integrate systems sharing data.
 Focuses on a centralized store of persistent data.
 If the store is passive it is called a repository or database.
 If it is active and informs users of changes it is termed a
blackboard.

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3. Virtual-machine:
 Support portability.
 Focuses on abstractions that give a complete service to their
users.
 Ex. Java Virtual Machine, which enables executable Java
code to be transported between machines.
3. Call–return:
 Support modifiability and scalability.
 Focuses on the sequence of computation.
 OO approaches are simply the current manifestation of this
style.

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5. Independent-components:
 Support modifiability.
 Decouples subsystems so that they
communicate symbolically and indirectly.
 Ex. the client–server approach to distributed
systems.

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The Input Output Application User
Interaction Architecture
 In object-oriented approaches this became known as
model–view–controller (MVC) architecture, which
equates model with application, view with output, and
controller with input.

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Frameworks
 Composed of an architecture, together with a
component repository with components suitable
for use within the framework, plus whatever
documentation would facilitate the use of the
framework.
 When a company wants to produce a range of
products based on a common framework it is a
called product line.

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The Product-line Process
1. Product-line initiation.
2. Domain analysis.
3. Architecture specification.
4. Component collection.
5. Specific-requirements capture.
6. Architecture specialization.
7. Component selection and specialization.
8. Integration and release.

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Topic Road Map
Components and Component Based
Development
Architectures, frame works and product
lines
 Patterns

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The Model View Controller
Architecture
The MVC architecture, or framework,
describes a high-level solution to the
general problem of human–computer
interaction, relating what the user sees on
a screen and does with a keyboard,
mouse or other interaction device, to the
functions of an application and the data
that it stores.

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Patterns Existing at Several Levels
Architectural patterns are the highest level
pattern.
Design patterns are the intermediate level
pattern.
Idioms are at the lowest level and include
program code level concepts.

From Model to Implementation II

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