Structured tools in SDLC

1. Tools of Structured Analysis
Chapter 6

2. Structured Analysis
• It is a set of techniques and graphical tools
that allow the analyst to develop a new kind
of system that is understandable to the user

3. Why do we use these tools?
• Use graphics whenever possible to help
communicate better with the user.
• Differentiate between logical and physical
system
• Build a logical system model to familiarize the
user with system characteristics and
interrelationships before implementation

4. Data Flow Diagram
• It was first developed by Larry Constantine as
a way of expressing system requirements in a
graphical form.
• It is also known as Bubble Chart

5. DFD Symbols
• Square defines a source or destination of
data.
• Arrow identifies data flow, means the data in
motion. It is a pipeline through which
information flows.

6. Continued…
• Circle or a bubble represents a process that
transforms incoming data flow into outgoing
data
• Open rectangle is a data store, or data at rest,
or a temporary repository of data

7. Constructing a DFD
• Processes should be named and numbered for easy reference
• The direction of flow is from top to bottom and from left to
right
• Data flow from the source to destination, although they may
flow back to a source
• When a process is exploded into lower level details, they are
numbered
• The names of data stores, sources, and destinations are
written in capital letters. Process and data flow names have
the first letter of each word capitalized

8. Data Dictionary
• A structured place to keep details of the
contents of data flows, processes, and data
store.
• It is a structured repository of data about
data.
• It is a set of definitions of all DFD elements

9. Advantages of Data Dictionary
• Documentation- it is a valuable reference in
any organization.
• It improves analyst/user communication by
establishing consistent definitions of various
elements, terms and procedures
• It is important step in building a database

10. Items to be defined in Data Dictionary
• Data Elements- smallest unit of data that provides for no
further decomposition.
For example: date consists of day, month and year
• Data Structure- a group of data elements handled as a
unit.
For example: phone is a data structure consisting of four data
elements: area-code-exchange-number-extension.
• Data Flows and Data Stores- data flows are data
structures in motion, whereas data stores are data structures
at rest. A data store is a location where data structures are
temporarily located.

11. Data Dictionary
Smallest Unit
of Data
Group of Data
Elements
Data
Elements
Data
Structures
Groups of
Data
Structures Data Flow Data Store

12. • For e.g.
Data Elements
Author Name:
First
Middle
Last
Alias
The Description of Data Element should include:
1. Name
2. Description &
3. An Alias (Synonym)

13. Data Elements
• Whether or not Data Element has the following:
– A Different Name:
• For e.g. A Purchase Order may exist as Pur. Order, Purchase
Ord., or P.O. We will record all these in Data Dictionary
under Definition of Purchase Order.
– Usage Characteristics
• Range of Values or Frequency of use or both.
• 2 types:
– Value within Range: For e.g. Payroll between 1000 and 10000 =
Continuous Value.
– Specific Value: For e.g. Depts. In a Firm coded 100 (Accounting),
110 (HR), 111 ( Operations) etc.

14. Data Elements
• Control Information
– Such as Source, Date of Origin, Users, or Access
Authorization.
For e.g. Looking for Properties of Word Doc.
• Physical Location
– In terms of Record of File or Database.
For e.g. Where Storage is done C Drive, D Drive,
CD ROM etc.

15. Data Structures
• It is the Group of Elements .
For e.g.
Data Structures: Book Details
Data Elements: Author Name (M)
Title of the Book (M)
ISBN (Optional)
Publisher Name (M)
Quantity Ordered (M)
Some Element are Mandatory whereas others are
Optional

16. Data Flows and Data Stores
• Data Flows = Data Structures in Motion
• Data Stores = Data Structures at Rest
For e.g.
Data Flow/Store Comments
Book Details From ABC Book Store
Edition 4th
Quantity 10 Copies
Customer Details

17. Decision Tree
• Once the data elements are defined in the
data dictionary, we begin to focus on the
processes.
• For example:
Bookstores get a trade discount of 25%; for
orders from libraries and individuals, 5%
allowed on orders of 6-19 copies per book
title; 10% on orders for 20-49 copies per book
title; 15% on orders for 50 copies or more per
book title

18. Type of Customer Size of Order DISCOUNT
DISCOUNT
POLICY
BOOKSTORE
LIBRARIES OR
INDIVIDUALS
6 OR MORE
LESS THAN 6
50 OR MORE
20 - 49
6 - 19
LESS THAN 6
25 %
NIL
15 %
10 %
5 %
NIL

19. Structured English
• Structures English is like structured
programming, it uses logical construction and
sentences designed to carry out instructions
• Designs are made through IF, THEN, ELSE, and
SO statements

20. An Example
IF order is from Bookstore
and-IF order is for 6 copies or more per book title
THEN: Discount is 25%
ELSE (order is for fewer than 6 copies per book title)
SO: no discount is allowed
ELSE (order is from libraries or individuals)

21. Continued…
ELSE (order is from libraries or individuals)
SO-IF order is for 50 copies or more per book title
Discount is 15%
ELSE IF order is for 20 to 49 copies per book title
Discount is 10%
ELSE IF order is for 6 to 19 copies per book title
Discount is 5%
ELSE (order is for less than 6 copies per book order)
SO: no discount is allowed

22. Decision Tables
• It is a table of possibilities foe defining a problem and the
actions to be taken
• It is a single representation of the relationships between
conditions and actions
• It consists of two parts: stub and entry
• The stub part is divided into an upper quadrant called the
condition stub and a lower quadrant called the action stub
• The entry part is also divided into an upper quadrant, called
the condition entry and a lower quadrant called the action
entry

23. Condition Stub Condition Entry
1 2 3 4 5 6
Customer is Bookstore Y Y N N N N
IF Order size 6 copies or more ? Y N N N N N
(Condition) Customer Librarian or Individual Y Y Y Y
Order-size 50 copies or more ? Y N N N
Order-size 20-49 copies ? Y N N
Order-size 6-19 copies ? Y N
Then Allow 25% Discount X
(action) Allow 15% Discount X
Allow 10% Discount X
Allow 5% Discount X
No Discount allowed X X
Action Stub Action Entry

24. Pros And Cons Of Each Tool
Which tool is the best depends' on a number of factors: the nature and complexity of the problem, the numher of actions resulting from the deci sions, and the
ease of use. In reviewing the henefits and limitations of each tool, we come to the following conclusions:
1. The primaty strengh of the DFD is its ability to represent data flows. It may he used at high 01" low levels of analysis and provides good system documentation.
However, the tool only weakly shows input and output detail. The user often finds it confusing initially.
2 The data dictionary helps the analyst simplifY the structure for meeting the data requirements of the system. It may be used at high or low levels of analysis, but
it does not provide functional details, and it is not acceptable to many nontechnical users.
3. Structured English is best used when the problem requires sequences of actions with decisions.
4. Decision trees are used to verifY logic and in problems that involve a few complex decisions resulting in' a limited number of actions.
5. Decision trees and decision tables are best suited for dealing with complex branching routines such as calculating discounts or sales commissions or inventory
control procedures.
Given the pros and cons of structured tools, the analyst should be trained in the use of various tools for analysis and design. He/she should use decision tables and
structured English to get to the heart of complex problems. A decision table is perhaps the most useful tool for communicating problem details to the user.
The major contribution of structured analysis to the system develop ment life cycle is producing a definable and measurable document-the structured
specification. Other benefits include increased user involvement, improved communication between user and designer, reduction of total personnel time, and
fewer "kinks" during detailed design and implementa tion. The only drawback is increased analyst and user time in the process. Overall the benefits oUtweigh the
drawbacks, which make structured analy sis tools viable alternatives in system development