Transcript TCS 2411 Software Engineering

Software Design Notations
“Documenting the software blueprint”
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Lecture Objectives
To describe the tasks in producing and
document the software design
To understand the systematic approach in
producing the different levels of the software
design
To illustrate the different notations that can be
used to draw the design
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Software Design
Next milestone, due on Week 9
Data design
 Database/File design
 Data structure design
Architecture design
Interface design
 Screen design
 Report design
Procedural design
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Design Model
Procedural
design
Interface
design
Architectural design
Data design
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Data Design
Select logical representations of data objects
(data structures) identified during
requirements definition and specification
Well-designed data can lead to better program
structure and modularity, and reduced
procedural complexity
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Data Design Tasks
Database/File design
Extension of Entity-Relationship Diagram
Entities  Tables
Attributes  Columns
Relationships  Columns, Tables
Describe database tables / files as follows:
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Data Design Tasks
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Data Design Tasks
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Data Design Tasks (Continued)
Data structure design
Arrays, structures/records, stacks, etc.
Describe structure and its use
Describe contents in similar way to database
tables/files
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Architecture design
Develop a modular program structure and
represent the control relationship between
modules
Can be represented by
Hierarchy of modules
Structure chart
Structure diagram
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Hierarchy of Modules
Process
File
Program
Read
File
Process
Record
Print
Record
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Generate
Report
Print
Error
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Structure Chart
Process
File
Program
no. of records
record
record
eof
Read
File
Print
Record
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Generate
Report
Process
Record
record
no. of errors
error
Print
Error
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Structure Diagram
Process
File
Program
while c1
Process *
Record
Read
File
Generate
Report
Check
Record
c2
Print
Record
Read
File
c3
o
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Print
Error
o
c1: not eof
c2: record ok
c3: error
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Interface design
Screen design
For text-based screens, can use design forms
Format: 25 rows x 80 characters
For GUI, can use ‘Print Screen’
Report design
For text-based reports, e.g. dot-matrix printers, use
design forms (80 or 132 columns)
For graphical reports, use ‘Print Screen’
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Procedural design
Details of how modules work
Define algorithmic details
Possible to use natural language
Structured form: pseudocode, or PDL (Program
Design Language), also called structured English
Clearer with graphical methods such as
Flowchart
Nassi-Schneiderman chart (N-S chart), box
diagram
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Structured Programming
Set of logical constructs from which any
program can be formed: Sequence, Condition,
Repetition
Limit procedural design to small number of
predictable operations
Enter at top, exit at bottom
Reduce complexity, easier to understand and
maintain
Program separated into logical ‘chunks’
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Flowchart Constructs
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Program Design Language(PDL)
if condition x
then process a;
else process b;
endif
if-then-else
PDL
easy to combine with source code
machine readable, no need for graphics input
graphics can be generated from PDL
enables declaration of data as well as procedure
easier to maintain
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Example of Pseudocode or PDL
Process File Procedure
Read file
While not end-of-file
If record ok then
Print record
Else
Print error
End if
Read file
End While
End
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Why Program Design Language?
can be a derivative for the HOL (High
Order Logic) of choice, e.g., Ada PDL
machine readable and processable
can be embedded with source code,
therefore easier to maintain
can be represented in great detail, if
designer and coder are different
easy to review
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Example of N-S Chart/ Box
Diagram Constructs
First task
Loop condition
Next task
Do-whilepart
Next + 1 task
Sequence
F Condition T
Elsepart
Thenpart
If-then-else
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Repeatuntilpart
Loop condition
Repetition
Case Condition
Value Value …..
Case- Case- …..
part
part
Selection
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Nassi-Shneiderman (N-S) charts/
Box Diagram Characteristics
Functional domain (i.e. the scope of repetition
or if-then-else) is well defined and clearly
visible as a pictorial representation
Arbitrary transfer of control is impossible
The scope of local and/or global data can be
easily determined
Recursion is easy to represent, where depicted
with a bounding pattern that encloses the
process (do-while part or repeat-until part) to
be repeated.
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References
“Software Engineering: A Practitioner’s
Approach” 5th Ed. by Roger S. Pressman, McGraw-Hill, 2001
“Software Engineering” by Ian Sommerville,
Addison-Wesley, 2001
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