Com S 362 Lecture Outline
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Reading: Chapter 2 from Baldwin and Clark

The textbook is available on reserve in the library.
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                 DESIGN PROCESS

Design (verb): Design is the process of inventing 
objects -- our "things" -- that perform specific 
functions. These objects, the products of human 
intelligence and effort, are called artifacts. 

Artifacts: have structure (what it is, how it is 
constituted?) and functions (what it does, what it 
is for?)


Exercise: Explain domain models and sequence diagrams
Exercise: Class diagrams and interaction diagrams

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                 DESIGN ARTIFACTS

Design (noun): Design is an abstract description 
of an artifact. It describes both structure and 
function. The design, however, need to precisely 
and completely describe the structure of the 
artifact. Functions may not be completely 
specified. 

Q: Why functionality need not be completely specified?




Exercise: Think about the initial purpose (function) 
of designing unix utility wc, now think about its 
use in the command ls -al | wc -l. Were this use 
and other similar usage anticipated?



Exercise: Think about the design of a stack of 
objects. Same design may serve different purposes, 
method call stack, postfix expression evaluation 
stack, etc.

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               DESIGN PARAMETERS

Design parameters: A design can be broken down into 
smaller units, called design parameters.

Example: 

Red mug and blue mug differ in terms of design 
parameter "color".

Polo's and Tees differ in terms of design 
parameter "collar type".

Design parameters have range. For example, mug 
could have a choice of colors red, blue, green, 
black, and white. In that case, the range of the 
design parameter will be the set {red, blue, 
green, black, white}.

Space of design: n-dimensional co-ordinate system, 
each axis represents a design parameter. When we 
give value to all co-ordinates, we get a point 
in the design space (i.e. a design). 

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            HIERARCHICAL DESIGN PARAMETERS

Hierarchical Design Parameters: Design parameters, 
certain choices of which bring new design parameters 
into existence in the design space. 

Example: Consider a design space of two subsystems 
{A, and B} and interconnection between these subsystems
{A-B}. 

The initial design space is {A, B, A-B}, i.e. the 
design parameters are the choice of module A, module B, 
and the choice of interconnection between the modules. 

The range of the design parameter interconnection is 
{true, false}, i.e. whether these two modules are 
interconnected or not, however, if the value of the 
design parameter interconnection is set to true a new 
set of design parameters comes into existence. 

For example, interface between these two modules need 
to be determined, i.e. a design decision about design 
parameters invocation {Explicit, Implicit}, 
concurrency {Asynchronous, Synchronous}, etc will 
have to made.  

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           DESIGN PARAMETER INTERDEPENDENCE

Design parameter interdependence: Often design 
parameters depend on each other is complex ways. 
For example, in the expanded design space of the 
example above {A, interfaceA, B, interfaceB, 
invocationA-B, concurrencyA-B}, the choice of the 
interconnection invocationA-B affects the choices 
that can be made for design parameters interfaceA 
and interfaceB. If invocationA-B is selected to 
be explicit, A's use of B affects interfaceB and 
vice versa. If invocationA-B is selected to be 
implicit, choices of interfaceA and interfaceB 
will have to include declaring and announcing 
events.

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          DESIGN STRUCTURE MATRIX

Design Structure Matrix: A tool for formally 
mapping hierarchical relationships and 
interdependencies among design parameter 
[Donald Steward 1981, Steven Eppinger 1991,1997]. 

 - A square matrix
 - Design parameters as rows and columns
 - Initiating and resulting parameter in columns and rows.  
 - X's to denote hierarchies 
 - X's in symmetry to denote interdependencies

Design Tasks: Choose the value of design parameters

Design structure: List of design parameters and 
the interdependencies among them.

Task structure: List of design tasks and connections 
between these tasks.

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