The Tools of Structured Analysis:

The Data Flow Diagram

The first step is to draw a data flow diagram (DFD). The DFD was-first developed by Larry Constantine as a way of expressing system requirements in a graphical form; this led to a modular design.

A DFD, also known as a "bubble chart,’’ has the purpose of clarifying system requirements and identifying major transformations that will be­ come programs in system design, So it is the starting point of the design phase that functionally decomposes the requirements specifications down to the lowest level of detail. 

A DFD consists of a series of bubbles joined by lines, The bubbles represent data transformations and the lines represent data flows in the system. The system takes orders from the customer (bookstore, library, etc.), checks them against an index (file) listing the books available, verifies. Customer credit through credit information files, and authorizes shipment with an invoice.

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

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

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.

Decision Tree

A decision tree is a decision support tool that uses a tree-like graph or model of decisions and their possible consequences, including chance event outcomes, resource costs, and utility. It is one way to display an algorithm. Decision trees are commonly used in operations research, specifically in decision analysis, to help identify a strategy most likely to reach a goal. If in practice decisions have to be taken online with no recall under incomplete knowledge, a decision tree should be paralleled by a probability model as a best choice model or online selection model algorithm. Another use of decision trees is as a descriptive means for calculating conditional probabilities.

Structured English

Structured English borrows heavily from structured programming; it uses logical construction and imperative sentences designed to carry out instructions for action. Decisions are made through IF, THEN, ELSE, and so statements. The structured English for our publisher's discount policy is shown

COMPUTE-DISCOUNT

Add up the number of copies per book title

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 individual customers)
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 SO:(order is for less' than 6 copies per book order) no discount is allowed
MEDIUM: 20 to 49 copies LARGE: 50 or more copies

From these examples we see that when logic is written out in English sentences using capitalization and multilevel indentation, it is structured English. In this tool, the logic of processes of the system is expressed by using the capitalized key words IF, THEN, ELSE, and so. Structures are indented to reflect the logical hierarchy. Sentences should also be clear, concise, and precise in wording and meaning.