Structured Analysis

Structured Analysis Graphic, 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 Decision Table

Data Flow Diagram A 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.

DFD It has four symbols 1. External Entity 2. Data Flow 3. Data Store 4. Process

Explation of symbols of DFD The 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 DFD The 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. Input Process Output

Advantages of DFD Understanding 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 DFD Physical consideration neglected. Large number of alteration. Ambiguous.

Data Dictionary Data Element DD 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 Data structure Data Flow Data Store

Data Dictionary Classes 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 Dictionary Valuable reference Improves communication Compare data description Cross reference Build database Disadvantage is that it do not provide details

Structured English It 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.

Example Structured 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.

5% DISCOUNT AND AN ADDITIONAL 5% DISCOUNT Decision Trees They 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 CUSTOMER? PREFERRED ORDER MORE THAN $1000? USED OUR CHARGE CARD ? $25 BONUS COUPON NO $5 BONUS COUPON 5% DISCOUNT AND AN ADDITIONAL 5% DISCOUNT 5% DISCOUNT

Advantages of decision tree Easy to understand Business rues are mapped easily Real problems solved No prior assumptions Process both numerical and categorical data

Disadvantages of decision tree Output attribute must be categorical Limited to one output attribute only Decision tree algorithms are unstable complex

Decision Table It 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 table Defines problem and actions Relationship between condition and action Two parts :- (1) stub (2) entry Stub has two parts:- (a) condition stub (b) action stub Entry has two parts (a) condition entry (b) action entry

Decision table diagram Condition Stub Condition Entry 1 2 3 4 5 6 7 8 Preferred customer Y Y Y Y N N N N Ordered more than $1000 Y Y N N Y Y N N Used our charge card Y N Y N Y N Y N 5% discount x x Additional 5% discount x $ 25 bonus coupon x $5 bonus coupon x x x x x Action stub Action entry

Advantages of decision table Concise description of logically complex situation Easier to draw and change than flow charts Easier to follow a particular path down one column than through several flow charts pages Limitation large decision tables can become difficult to modify