Structured Analysis
Structured AnalysisGraphic, easy to understand Partitioned process, clear picture of progression from general to specific
Logical rather than physical Precise, concise and highly readable
Tools of structured analysis
Data Flow Diagram
Data Dictionary
Structured English
Decision Tree
Data Flow DiagramA DFD is graphical representation which shows
the ‘FLOW OF DATA’. It is used for the visualization of data processing
for structured design.It shows interaction between the system and
outside entity.It is also called bubble chart. It is starting point in the system design that
decomposes to lowest level.It consist of series of bubbles joined by lines.
Bubbles represents transformations.
DFDIt has four symbols 1. External Entity 2. Data Flow
3. Data Store
4. Process
Explation of symbols of DFDThe EXTERNAL ENTITY symbol represents
source of data to the system. External entities determine system boundaries. They are beyond the area of influence of the developer.
The DATA FLOW represents movement of data. Data flow represents ‘DATA IN MOTION’. Data flows are always named. Names should be some identifying noun. For example: order, payment etc.
Explanation of symbols of DFDThe DATA STORE symbol represents data that is
not moving. Data stores are repository of for data. It is an ‘inventory’ of data. Data stores are named with an appropriate name. For example: Customers, Orders, Products.
The PROCESS symbol represents an activity that transforms or manipulates the data. Processes are actions performed on incoming data flows to produce outgoing data flows. All processes must have some inputs and outputs. Major functions of processes are making decisions.In
put
Process
Output
Advantages of DFDUnderstanding interestedness of
systems and sub systems.Communicating current system
knowledge to the user.Part of system documentation files.Logic underlining.Easy to follow errors.
Disadvantages of DFDPhysical consideration neglected.
Large number of alteration.Ambiguous.
Data DictionaryDD is structured repository of data. It keeps
the details of data flows, process and data stores. It documents the list of contents of all data flows.
It has three classes:- Data Element
Datastructure
DataFlow
Data Store
Data DictionaryClasses of DD are:-
1. Data elements: smallest unit of data further cannot be decomposed.
2. Data structure: group of data elements.
3. Data Flows and Data Stores: Data flows are data structures in motion. Data stores are data structures in store.
Advantages of Data DictionaryValuable referenceImproves communicationCompare data descriptionCross referenceBuild database
Disadvantage is that it do not provide details
Structured EnglishIt uses logical constructs to carry
out instructions for data (actions)Decisions are made through the use
of IF, THEN, ELSE and SO statements.
It is highly correlated to the decision tree.
ExampleStructured English version of the sales
promotion policy:- IF customer is a preferred customer , and IF customer orders more than $1000,
THEN apply a 5% discount, and IF customer uses
our charge card, THEN apply an additional 5% discount ELSE award $25 bonus coupon ELSE award $5 bonus coupon.
Decision TreesThey sketch out logical structure based on
some criteria. It is a graphical representations of the conditions, actions and rules found in a decision tree.
DIAGRAMATIC REPRESENTATION
PREFERREDCUSTOMER?
ORDER MORE THAN $1000?
USED OUR CHARGE CARD ?
$25 BONUS COUPON
NO
$5 BONUS COUPON
5% DISCOUNT AND AN
ADDITIONAL 5% DISCOUNT
5% DISCOUN
T
Advantages of decision treeEasy to understandBusiness rues are mapped easilyReal problems solvedNo prior assumptionsProcess both numerical and
categorical data
Disadvantages of decision treeOutput attribute must be categorical
Limited to one output attribute only
Decision tree algorithms are unstable
complex
Decision TableIt is single representation of the
relationship between conditions and actions.
A condition is usually given a value of ‘Y’ for ‘YES’, it is true, ‘N’ for ‘NO’ and a dash for ‘DO NOT CARE’.
Decision tree fails to tell us what conditions to test, a decision table can carry out the conditions to test.
Features of decision tableDefines problem and actionsRelationship between condition and
actionTwo parts :- (1) stub (2) entryStub has two parts:- (a) condition
stub (b) action stubEntry has two parts (a) condition
entry (b) action entry
Decision table diagram Condition Stub Condition
Entry 1 2 3 4
5 6 7 8Preferred customer Y Y Y Y N
N N NOrdered more than $1000 Y Y N N Y
Y N NUsed our charge card Y N Y N Y
N Y N
5% discount x xAdditional 5% discount x$ 25 bonus coupon x$5 bonus coupon x x
x x x Action stub Action entry
Advantages of decision tableConcise description of logically complex
situationEasier to draw and change than flow
chartsEasier to follow a particular path down
one column than through several flow charts pages
Limitation large decision tables can become difficult
to modify