Engr 691: Special Topics in Engineering Science
Software Architecture
Spring Semester 1998
Lecture Notes
Introduction
Acknowledgements: This material is based primarily on
Chapter 1 of the textbook for this course, Software
Architecture: Perspectives on an Emerging Discipline by Mary
Shaw and David Garland (Prentice Hall, 1996).
Thanks to Wen Wen Xu for entering my handwritten slides as HTML so
that I could prepare these notes more quickly.
What is Engineering?
- Many definitions include a phrase similar to:
-
- creating cost-effective solutions
- to practical problems
- by applying scientific knowledge
- building things
- in the service of mankind
- Key approach:
- codify scientific knowledge about a problem domain in a form
directly useful to practitioners
(and hence extend the capability of the ordinary design talent)
- Question:
- Is software development an engineering discipline?
Engineering Design
Engineering Design
| routine |
<====> |
innovative |
| familiar problems |
| unfamiliar problems |
| reuse prior solutions |
|
novel solutions |
| (handbooks, manuals) |
|
|
- Question:
- What is the situation with software design?
Software Reuse
Reuse of software
| code |
<===> |
design |
Problems in reuse:
- identifying reusable entities
- expressing them in useful form
- making them accessible
- adapting them to variants of the problem
- overcoming cultural tradition
- educating designers/programmers in reuse
- convincing management to invest in reuse
Figures from the Shaw and Garlan Textbook
Examine Figure 1.2, Evolution of an Engineering Discipline.
Examine Figure 1.3, Codification Cycle for Science and
Engineering.
Examine Figure 1.4, Evolution of Software Engineering.
Codification through Abstraction
- Abstraction:
- emphasizing the essentials, ignoring the details
Computer science has progressed by increasing the level of
abstraction---moving to larger conceptual building blocks.
(The following dates are approximate.)
|
1950's
|
machine language
symbolic assemblers
macro processors
simple compilers (e.g., early Fortran)
|
|
|
1960's
|
data typing (Algol)
modularity
user-defined types
|
|
|
1970's
|
theory of abstract data types
early OOP ideas
module interconnection languages (MIL)
|
|
|
1980's
|
. . .
class libraries
|
|
|
1990
|
CORBA
application framework
patterns
. . .
|
|
Aspects of the Emerging Science
- programming language abstraction (previous section)
- algorithm analysis
- automata/models
- language theory
What is Software Architecture?
It involves description of:
- elements from which systems are constructed
- interactions among those elements
- patterns that guide their composition
- constraints on those patterns
Systems are defined in terms of:
- collection of components
- interactions among those components (connectors)
Example components:
- clients and servers
- databases
- filters
- layers in hierarchical system
- etc.
Example interactions:
- procedure calls
- shared variables
- piped streams
- client-server protocols
- database transactions
- event multicast
- etc.
System Design
There are many levels of design, each with own concerns.
Each level consists of:
- components (vocabulary)
- rules of composition (syntax)
- rules of behavior (semantics)
Software Design
-
- Architecture:
- high-level system capability
-- involves composing modules to form systems
-
- Code:
- algorithms and data structures
-- involves composing primitive language features to form modules
-
- Executable:
- allocation of code and data to machine
-- involves composing bit patterns to form language features
Research Areas in Software Architecture
- architectural description languages
- codification of architectural expertise
- architectural frameworks for specific domains
- formal foundations
- architecture design/analysis selection methods
- support tools
- architecture extraction, recovery, and reengineering
(for legacy systems)
- etc.
UP to ENGR 691 Lecture Notes root document?
Copyright © 1998, H. Conrad Cunningham
Last modified: 15 January 1998.