Softenr-8

(1)

Software Engineering

Software

Project Design

Course Supervisor: Ms.

Asia Samreen

(2)

Chapter-09: Architectural Design

• _Objectives

–

_{Architectural Design}

–

_{Arch-Design Importance}

–

_{Arch-Design Patterns}

–

_Archetypes

–

_ADL

(3)

3

Why Architecture?

The architecture is not the operational software.

Rather, it is a representation that enables a software

engineer to:

(1)

analyze the effectiveness of the design

in meeting

its stated requirements,

(2)

consider architectural alternatives

at a stage when

making design changes is still relatively easy, and

(3)

reduce the risks

associated with the construction of

the software.

(4)

4

Why is Architecture Important?

• _{Representations of software architecture are an enabler}

_for

communication between all parties (stakeholders) interested

in the development of a computer-based system.

• _{The architecture highlights early design decisions}

_{that will}

have a profound impact on all software engineering work that

follows and, as important, on the ultimate success of the

system as an operational entity.

• _{Architecture “constitutes a relatively small, intellectually}

(5)

5

Architectural Descriptions

• _{The IEEE Computer Society has proposed}

IEEE-Std-1471-2000,

Recommended Practice for Architectural Description of

Software-Intensive System,

[IEE00]

–

to establish a conceptual framework and vocabulary for use during the

design of software architecture,

–

to provide detailed guidelines for representing an architectural

description, and

–

to encourage sound architectural design practices.

• The IEEE Standard defines an

architectural description

(AD)

as a “a collection of products to document an architecture.”

–

The description itself is represented using multiple views, where each

(6)

6

Architectural Genres

• _Genre

_{implies a specific category within the}

overall software domain.

• _{Within each category, you encounter a number}

of subcategories.

–

_{For example, within the genre of}

_buildings

_{, you would}

encounter the following general

styles:

houses,

apartment buildings, office buildings, industrial

building, warehouses, and so on.

–

_{Within each general style, more specific styles might}

(7)

7

Architectural Styles

• Data-centered architectures

• _{Data flow architectures}

• Call and return architectures

• _{Object-oriented architectures}

• Layered architectures

Each style describes a system category that encompasses:

(1)

(1)a a set of components (e.g., a database, computational modules) that (e.g., a database, computational modules) that perform a function required by a system,

perform a function required by a system,

(2)

(2)a a set of connectors that enable “communication, coordination and that enable “communication, coordination and cooperation” among components,

cooperation” among components,

(3)

(3) constraints that define how components can be integrated to form the that define how components can be integrated to form the system, and

system, and

(4)

(4) semantic models that enable a designer to understand the overall that enable a designer to understand the overall properties of a system by analyzing the known properties of its

properties of a system by analyzing the known properties of its constituent parts.

(8)

8

(9)

9

(10)

10

(11)

11

(12)

12

(13)

13

(14)

14

(15)

15

Architectural Design

• _{The software must be placed into context}

–

_{the design should define the external entities (other}

systems, devices, people) that the software interacts with

and the nature of the interaction

• _{A set of architectural archetypes should be identified}

–

_An

_archetype

_{is an abstraction (similar to a class) that}

represents one element of system behavior

• _{The designer specifies the structure of the system by}

defining and refining software components that

(16)

16

Architectural Context

target system: Security Function uses uses peers homeowner Safehome

Product Internet-based _system

(17)

17

Archetypes

Figure 10.7 UML relationships for SafeHome security function archetypes (adapted from [BOS00])

Controller

Node

communicates with

(18)

18

Component

Structure

SafeHome Executive External Communication Management

GUI Internet Interface

Function selection

(19)

19

Refined Component Structure

sensorsensorsensor sensor sensorsensorsensor sensor External

Communication Management

GUI Internet

Interface Security Control panel processing detector management alarm processing Keypad processing CP display functions scheduler

(20)

20

Analyzing Architectural Design

1. Collect scenarios. 1. Collect scenarios.

2. Elicit requirements, constraints, and environment description. 2. Elicit requirements, constraints, and environment description. 3. Describe the architectural styles/patterns that have been chosen 3. Describe the architectural styles/patterns that have been chosen to address the scenarios and requirements:

to address the scenarios and requirements: •

• module viewmodule view •

• process viewprocess view •

• data flow viewdata flow view

4. Evaluate quality attributes by considered each attribute in 4. Evaluate quality attributes by considered each attribute in isolation.

isolation.

5. Identify the sensitivity of quality attributes to various 5. Identify the sensitivity of quality attributes to various architectural attributes for a specific architectural style. architectural attributes for a specific architectural style.

6. Critique candidate architectures (developed in step 3) using the 6. Critique candidate architectures (developed in step 3) using the sensitivity analysis conducted in step 5.

(21)

21

(22)

22

(23)

23

Architectural Complexity

• _{the overall complexity of a proposed architecture is assessed by}

considering the

dependencies

between components within the

architecture [Zha98]

–

_{Sharing dependencies}

_{represent dependence relationships among}

consumers who use the same resource or producers who produce

for the same consumers.

For example, for two components u and v, if u and v refer to the same global data, then there exists a shared dependence relationship between u and v.

–

_{Flow dependencies}

_{represent dependence relationships between}

producers and consumers of resources.

For example, for two components u and v, if u must complete before control flows into v

(prerequisite), or if u communicates with v by parameters, then there exists a flow dependence relationship between u and v.

–

_{Constrained dependencies}

_{represent constraints on the relative flow}

of control among a set of

activities.

For example, for two components u and v, u and v cannot execute at the same time (mutual